M1 Garand failure to return to battery

[edwardware]

I have a new-to-me-from-CMP CMP Special M1 that fails to return to battery about 50% of the time. It looks like this:

Observations:
1) This only occurs when firing. No amount of dry fire or manipulation will reproduce it. I've only ever fired HXP 65 and 66 through it (bought from CMP). I'm at ~30 rounds since receiving it.
2) Obviously the cartridge isn't involved. The bolt is free and can be wiggled in it's track; it's not stuck. The follower is free and can be depressed against the spring. Depressing/releasing the follower does not free the jamb.
3) The op rod is jammed, with considerable friction, against something. I can smack it forward to close the action, or pull it back to open the action. The condition might persist for one manual cycle of the op rod but then will clear up. It never recurs when manually cycling, only when firing, and only about 50%. Sometimes it happens on the last round after the clip is gone.
4) The gun is greased/oiled to spec, more so since I've been seeing this error, and especially the barrel/op rod interface. Both barrel and op rod are worn through the park' where they rub, but they're plenty greased.

This rifle's twin run like a top. I've held the two actions and op rods up to each other, and I can't see anything that sticks out as different.

What should I be looking for or trying? Is it time to write CMP?

edit: tilt test comes back fine.

 

[NIGHTLORD40K]

My vote is bent op rod. You could remove the return spring and do a tilt test, or just swap out the known good rod from your other gun. The rod has too many critical dimensions to eyeball it unless the bend is obvious, and at that point it wouldn't run at all.
The rod rear retainer tab could be worn out too, resulting in it trying to jump the track.
If it wasn't a CMP gun, I'd say look for a crooked track due to a receiver reweld, but.......

 

[entropy]

Replace the op rod and the spring, it's cheap insurance. (the spring, the op rod ain't cheap!)

 

[GRIZ22]

I'd call CMP. They have great customer service. If it's the oprod they ain't cheap.

 

[NIGHTLORD40K]

Dupage trading usually has a good selection of op rods at very reasonable prices.

 

[edwardware]

My vote is bent op rod.

Replace the op rod and the spring,

I'd call CMP. . .If it's the oprod they ain't cheap.

So, a bent op rod seems a popular guess. I guess I'll write CMP and see what they say; hopefully if that's it they'll set it right.

If I swap op rods between the two rifles, and the failure follows the rod, I guess that'll seal it.

 

[shooter1niner]

Measure the spring. I believe the op rod spring should be between 19-3/4" - 20-1/4" free length. The spring also feeds the cartridges up by pushing on the follower. A weak or short spring may be the culprit. I have read that increased power springs should be avoided. Supposedly " Orion 7 " carries mil spec springs.

As mentioned earlier the " tilt test " both in and out of the stock will tell if there is a problem with the rod binding in its travels or rubbing on the stock.

 

[GRIZ22]

So, a bent op rod seems a popular guess. I guess I'll write CMP and see what they say; hopefully if that's it they'll set it right.

If I swap op rods between the two rifles, and the failure follows the rod, I guess that'll seal it.

You can do that if you want but I'd just call CMP and send it back to them.

 

[NIGHTLORD40K]

Yup, try the known good rod in the suspect gun, see what happens.
If the rod is the culprit, but passes a tilt test, then I would surmise the tab is worn out and it is trying to jump the track when subjected to firing stresses. In either case, replacing the rod should take care of the problem.

 

[Sunray]

"...new-to-me-from-CMP..." As in you bought it from the CMP? Fairly recently? Of so the op rod isn't bent. They check that sort of thing.
"...write CMP..." Call or E-Mail 'em. https://thecmp.org/training-tech/armorers-corner/
"...they ain't cheap..." Is being polite. Over $200 from Gunparts for an M1 op rod.
However, that's an ejection and/or extraction failure. Look at the gas hole and tightness of the gas tube. Then wear on the op rod thingy that fits in the receiver.
The TM's and FM's are here in .pdf format. Note the need for the provided UN & PW. It's FM-23-5 and TM-9-1275. And Fulton Armory is just stupid. It's spelt Ordnance. snicker. And buy a copy of Hatcher's Book of the Garand. About $30 on Amazon. Has the TM/FM trouble shooting in it.

 

[edwardware]

After an email chat with Larry at CMP I swapped op rods between my two rifles and shot the test Wednesday.

The jam stayed with the rifle (fitted with the 'good' op rod). I was able to pull the trigger group and stock off the action without disturbing the jab; I find that the binding is between the op rod piston and the gas cylinder!

Dropping the cylinder at home, it was dirty but not excessively so. After cleaning it has some clear scoring (see pic). The piston measures 0.5265 and is within 0.0005 of round; I don't have tools to
gauge the cylinder. I guess the piston wiped the cylinder clean when cycled by hand, but some heat and fresh fouling is enough to bind it up and prevent it from returning to battery

Pending clarification from CMP, I'm going to continue shooting after a thorough scrubbing of the cylinder and see how long it takes to recur. I have to assume that I have an undersized or out-of-round
cylinder and just enough carbon from ~40 rounds fired to bind the two together.