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

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[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.