7.62 M1 Garand sticky chamber

[boatbod]

After recently acquiring an M1 with a 7.62x51 barrel I found out that I'd bought a project rather than a finished gun. As it turned out, the short chambered barrel had been installed but never finish reamed/headspaced. Being the practical sort, with a modest engineering/machining background, I figured I'd obtain a pull through reamer & a set of gauges and complete the job myself. After lapping the bolt lugs and doing the reaming I ended up with what I thought was going to be a good chamber that nicely closed on the go gauge but not on a nogo.

After a trip to the range it seems I've got several problems to work on. They could well be caused by the same underlying issue.
i. Short stroking frequently. Maybe 85% of shots require manually cycling the bolt.
ii. Extractor ripping case rims sometimes.
iii. One complete failure to extract requiring a cleaning rod to knock the casing out.

Having examined the fired brass and what I can see of the chamber, it looks like there are machining marks in the rear half of the chamber that are being transferred to the brass making it extremely sticky and hard to extract.

The attached photos show two fired cases - the black one I covered in magic marker before dropping back in the chamber and letting the bolt slam home. Had to lever the bolt open to get it out again... I can see the majority of the rub marks correspond to the series of rings seen on the second casing which I polished with emery cloth.

If I'm right about the sticky chamber causing the short stroking, it should just be a matter of polishing it, but can this realistically be done without removing the barrel from the receiver?

Comments and suggestions most welcome!
---
Ammo was a mixture of commercial 150gr .308 and Peruvian FAME 147gr 7.62x51.
Gas port in barrel was measured at .096"
Tilt test passes
I haven't gauged the gas cylinder or mic'd the piston yet.
---

Thanks
/boatbod

[muffett.2008]

Chamber reamer is probably new and designed for commercial rifles , not sloppy like milspec.
Definately tight and a bit rough, though I don't think a polish will get you out of this to easily. I f you reload you could try dropping your loads slightly to give a bit more time for pressure to drop before extraction takes place, maybe the case can spring back by then, instead of being still locked against the chamber walls.

An old trick I have used before is to full length size and decap a case, drill through the primer hole and thread to suit your cleaning rod, slit the case down one side only along the case wall. Insert a cut of piece of fine wet and dry paper to form a half wrap around, insert into chamber with a squirt of dwf as lubricant, insert rod from muzzle end and engage thread, lightly lap using turning motion and keep lubricated.
If done correctly you should clean up the rear of the chamber in the area in question.
Good luck.

[browningautorifle]

Reamers are reamers. A new one does a good job and gives no trouble. The ammo should be SAAMI spec to begin with. I used a new Clymer reamer to do my 7.62 and have had NO failure of this kind. You definitely have a rough chamber, but it seems you're not really in a position to sort it out. You can't go in ankle deep. To fix a rough chamber you have to polish from the rear and straight in or you can cause a wear pattern to one side. Taking a barrel off isn't a big thing to me. I made the tools and it's easy. Maybe not for you.

The ammo you're using could have a steeper high pressure curve, there are men here that will know thiss ammo. I've not seen this stuff. You may also be able to tame it with an adjustable gas plug which would possibly end the rims ripped off and dropped casings. Also your extractor could be at fault but I don't think so. It sounds like there's so much pressure the bolt is moving too fast for the rim to hold. I saw this with an M1A in the '70s. The ammo was at fault there.

The thing is your problems are all over the map. Sounds like you have to re-engineer this gun from the buttplate forward.

[chuckindenver]

i stopped using a go gage long time ago, i check with a live factory round {remove your firing control first} it should close smoothly on a commecial factory round, i dont use military ammo for chamber checking, as you run into the issues you have other countries have different ideas of quality control.
after reading your post, it doesnt say that you actually finish reamed the chamber, only that your were planning on doing so, if you havnt finish reamed the chamber...stop shooting the rifle, and do so, or pay a gunsmith to do it right for you.. will be the best 50.00 you can ever spend.

[browningautorifle]

I was waiting or you to jump in Chuck...

[boatbod]

Reengineering the gun from the buttplate forward unfortunately sound about right. :(

Yes I did finish ream the chamber - previously the bolt wouldn't close at all on either a go gauge or a commercial round, so clearly it had never been finished when the barrel was installed. Prior to reaming I also checked the barrel timing to make sure I wasn't going to have to have problems there, and during reassembly I went through the gas cylinder & lock to put them in the right place.

Curiously, the forward half of the casings where the pull through reamer did it's cutting showed no tool marks at all. The roughness and ringing all appears to be in the rear 50%, which correspond to is the area cut by the barrel manufacturer and untouched by the finish reamer.

Yes I suppose the real answer is to pull the barrel and work on it from the chamber end. Really the only thing stopping me is the lack of an action wrench and barrel block. I'm confident enough in my abilities to do it and not hose it up, but at the same time, if there is a way to do it without removing the barrel then that has a certain appeal considering the cost of the tooling and the fact that both CMP and Midway are out of stock. Brownells has the tools in stock, but at a significant premium....

The concept of mounting a cut down casing on a cleaning rod appear to have merit, but I have some concerns whether I should use a fired case or one from virgin commercial ammo. Seems like the fired case would be a very snug fit, and since I currently have no reloading equipment, resizing with a full length die is not an option.

ETA: I notice the necks of fired cases show rifling marks from the throat. I can't imagine this is enough to stick the case in the chamber, considering the problems seen further back, but it does make me wonder whether this is normal stretching or not.

Thanks for the input. Keep it coming!
/boatbod

[chuckindenver]

i think you need to run the finish reamer in the chamber again.. what i do is, turn and cut till it smooths out, them with no pressure, make 2 more turns, then remove and check function.
be careful you can push the tool beyond its limit, when you feel it stop cutting then usually its done, i run it 2 times around to smooth out the cuts.

[browningautorifle]

Or...you could just box it up and send it to Chuck and forget it. Then it's his problem! When it comes home, it's good to go.

[boatbod]

i think you need to run the finish reamer in the chamber again.. what i do is, turn and cut till it smooths out, them with no pressure, make 2 more turns, then remove and check function.
be careful you can push the tool beyond its limit, when you feel it stop cutting then usually its done, i run it 2 times around to smooth out the cuts.

I can certainly try that and there is extra headspace available. I can see how that will help with the the case mouth engaging the throat but that's not going to do anything for the rear of the chamber where the reamer has no relief ground into the flutes. What I think I really need it about two turns of a conventional finish reamer that works across the full length of the chamber, rather than the pull through that only appears to cut on the shoulder and throat.

---------- Post added at 08:53 PM ---------- Previous post was at 08:52 PM ----------


Or...you could just box it up and send it to Chuck and forget it. Then it's his problem! When it comes home, it's good to go.

I guess, but there's nothing like a technical challenge to get me motivated to "go fix it".

[chuckindenver]

i thought about this...if you have rifling marks in the cases, then chances are you went too deap..looking at your cases you have pictured, looks like you may have an issue with the reamer, never seen a case that had milling marks in them...
maybe shoot a factory round, i found that remington cases work best for test fire. they run smooth, and dont have the machine gun crimps.

[boatbod]

i thought about this...if you have rifling marks in the cases, then chances are you went too deap..looking at your cases you have pictured, looks like you may have an issue with the reamer, never seen a case that had milling marks in them...
maybe shoot a factory round, i found that remington cases work best for test fire. they run smooth, and dont have the machine gun crimps.

I certainly can't discount a problem with the reamer since it is new, but I doubt I went too deep. The go gauge only just closes fully and the bolt lug only comes about 75% of the way closed on a nogo.

Now that you mentioned machine gun crimps, I went back and carefully inspecting some unfired rounds from the same box as the previously posted casing. Now that I look more closely I can confirm they do have faint crimp marks around the case mouth in the same 6-way pattern. Guess we can discount that as being part of the problem, especially since there are no similar case-mouth marks on cases from the Peruvian ammo that I fired at the same time. Both sets of brass do however show the same rings around the middle to rear areas, and rim damage is much worse on the Peruvian vs the commercial ammo. At this point I'm almost certain that those tool marks need to go away.

[browningautorifle]

If your chamber's as tight as you suggest then Chucks idea of a couple of turns with a finish reamer will do it. I've done that sort of thing and barely any metal comes off. The chamber's then fresh and new and your tight chamber's no more. Just be careful. I just don't know how you can do that as carefully with the barrel installed. You need an even pressure from the rear and straight in.

[boatbod]

I have two concerns with running a regular finish reamer in the chamber:
- given that the bad area is close to the breech, any success with a reamer would require the chamber to be tight in this area, otherwise it's just going to cut at the neck and throat again. The impression I get from hand feeding fresh rounds that the rear of the chamber may already be a little on the looser side in that area.

- as you say, running a reamer with out removing the barrel doesn't sound very practical since the only way of turning it would be with a small ratchet wrench or similar. The offset forces and lack of feel would make life tricky and probably not result in good accuracy.

Oh well, sounds like time to go shopping for a barrel vise and receiver wrench. :surrender:

[boatbod]

I pulled the barrel today, and was somewhat surprised that it was barely more than hand tight. Well let me correct that - my surprise lasted perhaps two seconds until I remembered that nothing else had been right with the gun, so why would this be any different...

Anyway, having gained access to the rear of the chamber I was able to lap away the circular machining marks using 800 grit compound smeared on a fired case. The case was spun with a cordless drill while being moved in/out, taking care to avoid coming up hard against the shoulder. The finished chamber appears uniformly gray, except for the shoulder which still had a few reamer marks.

After reassembly, the go gauge closed properly and the nogo didn't, so I'm confident that headspace is largely unchanged. Hopefully I'll get to the range in the next week or so to see if I've solved the extraction and cycling problem. I don't know if it counts for much, but a selection of fired cases can now be chambered and extracted without resorting to prying the bolt back. [They are still tight, as I would expect, but at least they pop out with a good tug on the operating rod.]

[browningautorifle]

Well...I still think it's not quite right, but you'll soon see. They should move in and out effortlessly. Chuck, do you want to take him through re-creating the crush factor of the barrel shank? Or lock-tite?

[chuckindenver]

i wouldnt use lock tite.
just peen the shoulder all the way around , and youll get one more crush fit..i use the rounded end of a ball peen hammer, just work the edge of the of the shoulder all the way around.
it will give you one good crush fit.

[boatbod]

The shoulder had previously been peened with a centerpunch - a real high quality Bubba job! With nothing to loose in that department, I added to it and got the barrel to draw up tight with the front sight correctly indexed. I though about loctite, but really with to sort of temps it might reach if fired enough, loctite wasn't going to stay tight for long.

I believe the real answer is to fabricate a breeching washer and set the shoulder back sufficiently to give the correct starting index. Any idea how many degrees before center an M1 barrel should be when assembled into the receiver just hand tight?

[chuckindenver]

a washer well ruin your headspace...a new barrel is the best fix..rolling the shoulder if done right fixes the issue.

[browningautorifle]

Like Chuck says, if you redo the shoulder and draw it up carefully it won't come undone nor will it ruin anything. I've done them and it works fine. Just do it correctly and leave it alone. Then shoot the pi** out of it.

[boatbod]

a washer well ruin your headspace...a new barrel is the best fix..rolling the shoulder if done right fixes the issue.

Headspace shouldn't change much, since the object is to end up with the barrel indexed in the same position it is now, just with more torque on the threads.
The procedure is described by Peter Laidler (http://photos.imageevent.com/badgerdog/generalstorage/peterlaidlerpostsleeenfieldforums/Breeching%20Up.pdf)

Yes, a new barrel would be the simplest solution...

[browningautorifle]

Then go ahead and do the washer. Let us know.

[chuckindenver]

remember...)( is a country mile when it comes to headspace..when adding even a paper then washer, your pushing that barrel out, pushing the chamber out,,extending the headpace out to dangerous lengths.
only fix on the barrel is to change it, if it were a bolt action or single shot, turning the shoulder, and the breach face would work.
on a semi auto with gas system, it doesnt work, shortening up the barrel, will break parts down the road..
a new commecial barrel costs less then 200.00

[boatbod]

Difference between go and field is 0.008" if I recall. Definitely do-able, but requires care.
What I'm going to do before exploring that avenue is go shoot what I've done so far and see if further tinkering is necessary. Looks like I'll have more time on my hands after Christmas, but sadly less spare $$ for a month or two. Experimentation not spending will be the name of the game.

[chuckindenver]

its been my experiance, every time iv tried a washer, even a thing brass or copper one thats thinner then paper, it was unsafe, on square threaded shouldered barrels.
the only square threaded barrel its worked on, is a Krag, as it crush is at the breach face, and a rimmed case.
i can relate to the less money, more time thing...

[browningautorifle]

If you re-created the crush factor with your pien of the shoulder, your barrel will be sufficiently tight to hold solid. You can't unscrew it with your hands anyway. I've had some very light torque barrels do just fine. Have faith. It'll be fine.

[boatbod]

Oh I wouldn't try to add a washer or shim without removing some material from the barrel shoulder first.

What I'd do is face off the shoulder to clean it up, screw the barrel into the receiver at say 10 o'clock and then measure with feeler gauges to determine how much gap I had. (e.g. 0.006") Next step would be to make a washer at some arbitrary but manageable thickness (e.g. 0.090") then do the math to figure out how much extra material had to be removed from the barrel shoulder. In this theoretical example, that would be 0.084".

The barrel should come up hand tight at 10 o'clock and would then need to be torqued until it reached index at 12 o'clock. Theoretically headspace shouldn't have changed by more than a thou or two if at all, since the threads would be engaging at the same place.

[JBS]

A recommended minimum thickness for your breaching washer is .050 plus what is needed to index at torque. Most smiths’ experience failure doing this because they attempt to use a shim washer instead of cutting the shoulder forward and making or using a true breaching washer. Good luck to you. :thup:

[boatbod]

If you re-created the crush factor with your pien of the shoulder, your barrel will be sufficiently tight to hold solid. You can't unscrew it with your hands anyway. I've had some very light torque barrels do just fine. Have faith. It'll be fine.

It's definitely light torque, but a fair bit more than hand tight. I definitely want to shoot it before doing anything further, but those darned family obligations are getting in the way!!

[boatbod]

Finally got to spend some time at the range.

The good news is that rims are no longer being destroyed. The empty cases looked pretty good, with the occasional ding at the mouth, but otherwise undamaged. Accuracy was pretty good considering my general lack of time on iron sights. Most shots were going into a 4" group at 100yds when fired from a bench. At 200yds I was reasonably reliably hitting a torso sized metal plate.

The bad news is that I'm still experiencing failure to feed once or twice per clip. Mostly when that happened the chamber is completely empty, however sometimes a partially fed round had hung up at an odd angle just off the mouth of the chamber.

On the surface this seems like a short stroking problem since I can't imagine how else you'd end up with an empty chamber, however, I do not recall a single incidence of the bolt failing to lock back after the 8th round was fired. :confused: Maybe friction from the bolt rubbing on the next round is enough to slow it down if it's already moving more slowly than in should?

Back to the workbench... I'm going to polish up a few cases to look for rings, and then I suppose I better mic the piston and find a way to gauge the gas cylinder.

[browningautorifle]

That's probably right. I wish I was a bit closer and it would be easier to help. If you can get another shooter(experienced) to watch, you may get some insight. What ammo are you using again? Maybe it doesn't have the poop? I don't think it's friction. There's sticky here somewhere in the M1/M14 forum to help with the malfunctions.

[JBS]

See if this helps locate the problem. I use this in my shop.

Section 10.
Paragraphs 40-51

MALFUNCTIONS AND CORRECTIONS_______________________________________ _
40. Scope
The malfunctions and corrections contained herein are supplementary to those contained in using arm manual FM 23-5. Although the same malfunction may appear in both the using arm manual and in this manual, the possible causes and corrective actions contained herein are in addition to those covered in the using arm manual. Therefore, when malfunctions are being corrected by ordnance personnel reference to FM 23-5 will be necessary.
41. Clip Inserts with Difficulty
If difficulty is encountered in inserting a loaded clip in the receiver of a rifle which has previously been loaded without apparent difficulty, it may be assumed to be caused by a deformed clip which should be discarded. However, if continued trouble is encountered in inserting loaded clips, it may be caused by one or more of the following reasons:
a. POINT OF CLIP EJECTOR TOO LONG
If the offset point of the clip ejector is too long, it may scrape against the side of the magazine aperture in the stock, thereby making it difficult to depress the clip ejector. Disassemble the barrel and receiver group and trigger housing group from the stock, then reassemble the two groups together without the stock. Note the position of the offset point of the clip ejector in regard to the outside face of the magazine of the receiver. If it protrudes beyond this face, the point of the clip ejector is too long. Remove the clip ejector from the trigger housing group in accordance with FM 23-5 and grind the offset point until sufficient clearance is obtained.
b. BURRS IN MAGAZINES.
With the trigger housing group removed from the receiver and the bolt retracted, examine the magazine for burrs. Burrs in the follower and slideways will prevent the follower and slide from functioning, thereby making it difficult to insert a loaded clip. Remove burrs with a fine-grained sharpening stone.
c. INTERFERENCE BETWEEN BULLET GUIDE AND FOLLOWER ARM.
Remove the barrel and receiver group from the stock and retract the bolt. With the right hand holding against the operating handle so that the bolt does not release, depress the follower and slide several times with the left hand and observe if interference is encountered between the bullet guide and follower arm. This interference is often caused by the opening in the bullet guide being "squeezed in" thereby causing the follower arm or follower rod to drag on the bullet guide. Remove the bullet guide from the receiver in accordance with FM 23-5 and with a suitable wedge spread the opening until suitable clearance is obtained between the bullet guide and follower arm.
42. Short Recoil
Short recoil stoppages, often confused with feed stoppages, occur in rifles which are underpowered; and therefore do not drive the operating rod completely to the rear. When a weapon is underpowered, and thus subject to short recoil stoppages, it will usually close on an empty chamber or fail to eject the fired case, closing with the spent case in the chamber. This is the type of malfunction which occurs most frequently in the rifles. In analyzing this type of stoppage, the possible causes listed below should be carefully checked:
a. UNDERSIZED PISTON. Refer to paragraph 20d.
b. OVERSIZED GAS CYLINDER. Refer to paragraph 20g.
c. UNDERSIZED BARREL AT SPLINED SECTION. Refer to paragraph 21f.
d. CARBON OR FOREIGN MATTER IN GAS PORT OF BARREL. Refer to paragraph 21f.
e. CARBON IN GAS CYLINDER. Refer to paragraph 21c.
f. OPERATING ROD BINDING. Refer to paragraphs 20d and 30,
g. VALVE LEAK IN GAS CYLINDER LOCK SCREW. Refer to paragraph 20g.
h. DEFECTIVE OPERATING ROD SPRING. Refer to paragraph 20c.
i. BOLT BINDING. With the follower rod and operating rod removed from the rifle, operate the bolt back and forth several times by hand and note where it is binding. The rear lug on the bolt dragging on the receiver and heavy or burred locking lugs are the two most common causes of a binding bolt. Remove the bolt from the receiver in accordance with FM 23-5 and with a fine, flat file or fine-grained sharpening stone remove just enough metal so that when the rifle is tipped up and down, the operating rod and bolt, with the follower rod and operating rod spring removed, will move from closed to open position and back by their own weight.
j. BURRS, FOREIGN MATTER AND IMPROPER LUBRICATION. Refer to Section 4.
k. RUSTY OR RINGED CHAMBER. Clean the rifle barrel in accordance with instructions contained in FM 23-5 and examine it as outlined in paragraph 9c of this manual. If barrel is unserviceable, refer to paragraph 22c for instructions on replacement.
43. Bolt Fails to Close Tightly After Fire.
This condition may be due to one or more of the following causes:
a. EXTRACTOR DOES NOT OPEN ENOUGH TO PASS OVER RIM OF CARTRIDGE. The most common cause of the extractor failing to open sufficiently to pass over the rim of the cartridge is chips or foreign matter lodged between the heel of the extractor and the locking lug on the bolt which houses the extractor spring plunger. Remove the extractor, extractor spring plunger assembly, and the cartridge ejector assembly in accordance with paragraph 19e. Clean all parts thoroughly. Check the extractor and extractor spring plunger for free action in their apertures in the bolt, as binding of these parts will prevent the extractor from opening.
b. OPERATING ROD BINDING. Refer to paragraphs 20d and 30.
c. WEAK OR BROKEN OPERATING ROD SPRING. Refer to paragraph 20c.
d. ROUGH OR DIRTY CHAMBER. Refer to paragraph 42 above.
e. INSUFFICIENT HEADSPACE. Refer to paragraphs 9c and 22d.
44. Failure to Feed.
Feed failures, as in the case of short recoil stoppages, may cause the weapon to close on an empty chamber. This may be caused by excessive bolt speed when the bolt moves so rapidly on the forward stroke that the ammunition does not have time to obtain its proper feeding position. This condition is often caused by unauthorized modification of the weapon, such as increasing the gas port diameter. (See par. 21f). It also may be caused by any of the following reasons:
a. INSUFFICIENT REARWARD TRAVEL FOR BOLT TO PICK UP NEXT ROUND DUE TO INSUFFICIENT RECOIL. Refer to paragraph 42 above.
b. LONG EJECTOR. If the ejector is too long and protrudes beyond the rim on the front of the bolt, the cartridge will be prevented from rising to its proper position in front of the bolt. Remove the ejector from the bolt in accordance with paragraph 19e and grind or file sufficient metal from the ejector so that it lies below the rim on the front of the bolt.
c. WORN OR IMPROPER FORMED FOLLOWER. A worn or improperly formed follower may cock or bind in its slideways in the receiver and thus prevent it from forcing the cartridge upward to its proper position in front of the bolt. Remove the follower and slide assembly and check angle of the follower as outlined in paragraph 21a. Replace a badly worn follower.
45. Bolt Fails To Release When Clip Is Latched.
This condition may be due to the following causes:
a. INSUFFICIENT RADII OR BURRS ON CATCH AND OPERATING ROD HOOKS. Insufficient radii or burrs on the hooks of the operating rod and operating rod catch may prevent them from "riding over" each other, thus preventing the bolt from releasing when the clip is inserted and latched. This condition may be remedied by lightly stoning the edges of the hooks with a fine-grained sharpening stone. Extreme care must be exercised when stoning so that the radii are not enlarged excessively as this will cause the bolt to release before the clip is latched. (See par. 46 below).
b. BULLET GUIDE LOW AT ACCELERATOR BEARING POINT. If the bullet guide is worn sufficiently at the accelerator bearing point (fig. 30), the follower arm acting upon the accelerator will fail to cam up the operating rod catch sufficiently for it to clear the operating rod hook and the bolt will not go forward when the clip has been inserted and latched. Replace bullet guide to correct this condition.
46. Bolt Releases Before Clip Is Latched.
The reverse of the causes of the bolt failing to release when the clips is inserted, listed in paragraph 45, above, may cause this condition. In addition it may be due to a defective clip latch or clip latch spring. If the radii on the hooks of the operating rod or operating rod catch are excessive and causing the bolt to go forward before the clip is latched, replace the parts. A bullet guide that is high at the accelerator bearing point should be removed from the rifle and stoned at this point until the accelerator will not cam up the operating catch sufficiently to release the operating rod until the clip is fully inserted and latched. Hand function the clip latch to see if this is not binding in the receiver and that the clip latch spring has sufficient tension to rotate the clip latch on its hinge pin. If there is binding, examine for burrs and remove by stoning or filing. If binding is due to deformation or improper dimensions, replace the clip latch. Replace a weak or broken spring.
47. Bolt Fails To Stay In Rearmost Position After Firing The Last Round. Clip Held Inside Of Gun, Jammed On The Way Out By The Bolt.
This condition may be caused by insufficient power to drive the mechanism rearward far enough for the operating rod to engage the catch (par. 42, above), a binding clip latch (par. 46,above), or the following: With the bolt fully retracted and latched and the follower at its uppermost position, examine the clip locking lug at the rear end of the clip latch to see if it clears the receiver. If it does not clear the receiver, the arm of the operating rod catch is either broken off or deformed to the extent that it does not rotate the clip latch sufficiently for the locking lug to clear the receiver and release the clip. Replace a broken or deformed operating rod catch.
48. Failure To Eject Cartridge Case.
This may be caused by a short recoil (par. 42, above) or one of the following reasons:
a. WEAK OR MISSING EJECTOR SPRING. Remove the ejectore spring from the bolt as described in paragraph 19e and replace.
b. EJECTOR BINDING. Remove the cartridge ejector from the bolt as described in paragraph 19e. Examine for burrs on ejector. Also check for burrs and foreign matter in ejector aperture in bolt.
49. Failure To Eject Cartridge Clip.
This condition may be due to one or more of the following causes:
a. CLIP EJECTOR WEAK OR BROKEN. Remove the clip ejector from the trigger housing group in accordance with FM 23-5 and replace.
b. DISTORTED CLIP.
c. DEFORMED OR BROKEN OPERATING ROD CATCH. Refer to paragraph 47, above.
50. Failure Of Bolt To Open After Fire.
This is probably due to one of the following reasons:
a. PLUGGED GAS PORT. A plugged gas port in either or both the barrel and gas cylinder will prevent the expanding gas from passing through these ports to drive the operating rod and bolt to the rear. Refer to paragraph 21c and f for corrective action.
b. LOOSE GAS CYLINDER. If the gas cylinder is sufficiently loose on the barrel of the rifle, enough of the expanding gas will escape around the barrel so that the gas acting on the piston through the gas ports will be insufficient to drive the operating rod and bolt to the rear. Check the diameter of the barrel at the gas port. (See par. 21f). If the barrel is undersize, replace. If the barrel is of correct size, replace the gas cylinder.
c. GAS CYLINDER LOCK SCREW VALVE OPEN. Refer to paragraph 20g.
51. Failure To Fire.
The possible causes of failure to fire listed below are in addition to those listed in FM 23-5:
a. WEAK OR BROKEN HAMMER SPRING. A weak or broken hammer spring may fail to drive the hammer forward against the firing pin with sufficient force to fire the cartridge. This is indicated by a light indent in the primer. Remove the spring from the trigger housing group as outlined in FM 23-5, and replace.
b. LOWER TANG ON HAMMER STRIKES STUD ON TRIGGER GUARD. The rear tang on the hammer striking the stud on the trigger housing will cushion the blow of the hammer against the firing pin or possibly even prevent it from going forward far enough to strike the firing pin. Remove the trigger housing group from the rifle, cock and release the hammer. Note if the rear tang on the hammer is striking the stud on the trigger housing. If the hammer does strike the stud, disassemble the trigger housing group as outlined in FM 23-5, and grind the tang on the hammer sufficiently to clear the stud when the hammer is in its forward position.

[boatbod]

I've tried a mixture of commercial 150gr .308 and milsurp 148gr 7.62x51 with no apparent difference in behavior. If it weren't for the previous rim bending/sticky chamber, I'd wholeheartedly think it's undergassed, but as it is I wonder whether the empties are still sticking a bit.

Tilt test is good, so I don't think it's an op-rod binding problem or anything like that.

ETA: empties are typically thrown to the 4 o'clock position about 5' from the bench. Some end up closer at around 3 o'clock.

[us019255]

its been my experiance, every time iv tried a washer, even a thing brass or copper one thats thinner then paper, it was unsafe, on square threaded shouldered barrels.

Chuck:
Please explain for me what happens when using a very thin breaching washer to change the timing, particularly when it is done before a locking shoulder is picked to set head space, what happens that makes the rifle unsafe?

---------- Post added at 09:16 AM ---------- Previous post was at 09:08 AM ----------

Oops! A senior moment disregard previous comments about locking shoulders. I was thinking FAL inre: locking shoulders. I guess I should rephrase. Assuming that after placing a thin brass or steel breaching washer and reassembling, you had the proper timing, and the headspace was still within specifications (stripped bolt does not close on field gauge), what would be unsafe about the rifle??

By the way, personally I probably would replace the barrel on a Garand, but have used, apparently successfully, breaching washers of various thicknesses on FAL builds.

[boatbod]

Did some measuring today:

The gas port is .099", which should be sufficient, although as a last ditch I might consider resizing it to .1065" to match the old Navy 7.62 barrels.

The gas piston mics at .5253", which is at the lower end of the spectrum but still within spec.

I couldn't measure the gas cylinder since I don't have a gauge, however the piston doesn't seem to be unduly sloppy when inserted.

The OD of the barrel at the gas port was .599" and is a nice snug fit on the gas cylinder. Some carbon fouling was present, suggesting a little leakage , but I'd imagine that's normal since there really is no way to "seal" the various components.

Mainspring was approximately 19" OAL. I have ordered a new one since there is some evidence of wear on some of the coils.

By far my most interesting discovery was that the underside of the bolt noticeably drags on the half-round cutout in the bridge. It only does it when applying downward pressure to the right hand locking lug or charging handle, or when lifting up on the op rod under the barrel. A tilt test works great either upright or inverted, but if you catch this problem just right it puts up considerable resistance.

From an operation perspective, the rubbing starts right as the right hand locking lug starts to enter into the rear of the receiver (approx .75" sticking out). This corresponds to a slight thickening/ramp on the underside of the bolt.

I tried polishing out some of the roughness from the bottom of the bolt using 400 and 600 wet/dry, but I'm not sure it made much difference. Coating the area with a black sharpie definitely proves this is the right spot, but since both the receiver and bolt are hardened, doing anything about it without resorting to the dreaded rotary tool is quite challenging.

Of course, the bigger question with whether this binding occurs when the gun cycles itself? It might explain the somewhat random appearance of short stroking symptoms.

[boatbod]

The new mainspring is about .75" longer than the old one.
Hopefully going to the range again tomorrow to see if changing it and smoothing the underside of the bolt fixes anything.

ETA: Updated range report 12/31

Short stroking was worse with the new spring. Single loaded rounds almost never resulted in the bolt locking back, and attempting to run with a clip inserted usually resulted in about 50% empty chamber and 30% misfeed.

After I got home I fabricated a .532" no-go gauge to check the gas cylinder, and was relieved to find that it did not slide in. Tomorrow I'll fabricate a .528" go gauge to check for out-of-round. If that checks out ok, the next step will be to open up the gas port from .099" to .1065" to match the Navy specs for their 7.62x51 barrel.

[tdeon221]

You need a new barrel. Get a Criterion. Be happy.

[browningautorifle]

We already broached that subject Tdeon and he ain't buyin'. The new spring doesn't surprise me because it's stronger. The larger gas port(to spec only) may help. Don't go bigger.

[boatbod]

If funds were unlimited I most certainly would get another barrel. For the time being I'm determined to make this one work, and I do believe I'm getting close.

The gas cylinder is a tight fit on a .528" gauge and exhibits no obvious out-of-roundness other than what looks like a relief cut at the rear.

Gas port has been enlarged to .1065" (#36) which is approximately a 15% increase in cross-section. Hopefully that's enough to make it run.

[boatbod]

It still doesn't run with NATO ammo, but it is able to lock the bolt back with 168gr Federal and the ejected brass gets flung a bit higher/farther so obviously bolt speed is increased as to be expected.

Polished the chamber some more, but there are still a few horizontal rings showing in the softer commercial brass, so quite possibly the only hope for this barrel is a couple turns with a full length finish reamer. :banghead:

Since a finish reamer is nearly half the cost of a new barrel, I need to consider my next move.

[tdeon221]

Did you cast the chamber/throat? Under 200 for a barrel. There is someone who rents reamers on the web.

Tom

[boatbod]

I've yet to try a chamber cast. Is is likely to reveal more than what can be seen with a flashlight and fired brass?

[tdeon221]

You'd see exactly what's up. A hawkeye borescope would work too. At this point just put a new barrel on it. You're at the point of diminishing returns. You've got the tools. With what you've done already I would expect 2"-4" groups at 200 from position with good ammo with a barrel change. Good being Sierra matchkings with about 41.5gr of IMR 4064(308). If that load doesn't work in any m1 or m14 something's wrong with the gun.

[boatbod]

So it seems Krieger make the best barrel, but how do they compare to the significantly less costly Criterions? Will the average shooter even notice the difference considering we're talking about a rifle with iron sights?

[tdeon221]

Criterion are button rifled and are made by Kreiger. To capitalize on the max accuracy potential of a barrel all national match mods should be done. So it depends what you want to do with it. Full course with a garand you need a quality barrel and all the tricks and you'll still have a hard time keeping up with the AR's. A games gun still needs a quality barrel but you're limited to what you can do to the rifle, you're also only shooting to 200 yards on the SR Target which has a three minute ten ring. You can shoot very small groups with iron sights, they're not a limiting factor.

[boatbod]

Went to help a buddy sight in his new bolt gun today, so used the excuse to sling some more lead downrange.

20rds of commercial .308 Winchester 150gr (2850fps) cycled fine every time while 147gr 7.62x51 still did not. I only bring this up because it was readily apparent the empty .308 cases were being flung considerably more aggressively than their 7.62 cousins. Curiously, unfired .308 was also a sloppy fit in the chamber, whereas the 7.62 felt pretty snug and had minimal noticeable vertical/side-side free play. Fired brass of both types mic'd at 0.470" just in front of the base, while the unfired (again of both types) was around 0.003" smaller. SAMMI says 0.4709" for a .308 which is right where we are.

At this point I've basically decided to put a new barrel on and move forward. Looking at the rear of the chamber through a 10x loupe shows a pretty rough finish, even after multiple sessions with the 800 grit compound. With that and the need to make a proper breeching washer to achieve decent torque at the correct index, it's just going to be easier to start over.

Even with the problems, this is still a fun gun to shoot! I never figured I'd be reliably able to plink an 18" square steel plate at 300yds with iron sights. Mr Garand makes it almost too easy :)

Thank you to everyone who got me to this point. Hopefully my next update will be once I have it fully sorted (when funds permit).