7.62 M1 Garand sticky chamber

[browningautorifle]

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

Information

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[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...

[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.

[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.

[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.