7.62 M1 Garand sticky chamber

[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.

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