M-1 Carbine Piston

[Retired W4]

Obviously not a S&W question but I thought someone here could help. I recently got a Winchester carbine from the first SN block and the piston is stuck in the forward position. It was fine when I started cleaning it but now it will not move. A friend loaned me his wrench for the retaining nut and I removed it. I have put acetone down around the piston and rapped the barrel with my plastic mallet and it will not come loose. Tried gripping with a padded vise grip and still nothing. Any ideas?

 

[LostintheOzone]

Heat gun. Old gunsmith trick to remove sights and frozen chokes.

 

[DWalt]

I take it that both the piston and the retaining nut have been removed, but the piston will not separate from the nut? I have seen pistons get sticky, but not frozen in place. At one time, carbine parts used to be readily available, do not know the situation today. Heat might work. Also maybe a soak in penetrating oil.

 

[Nick B]

Be real careful when installing the piston nut . Don't over tighten.
I've seen the piston channel split from over tightening.

 

[SnidelyWhiplash]

Give it a good soaking with some Kroil...that will loosen most anything.

 

[smoothshooter]

Try the 50/50 acetone and ATF mix and let it soak for a few days.
Rumored to be the best penetrant out there bar none.

 

[Matt_X]

If there was no known issue before, I'd put the nut back on and shoot it.That should free it. Or was there a problem? failure to cycle the slide?
Juggernaut's 1944 Inland 50668** - The Carbine Collector's Club

need advice on freeing stuck gas piston - The Carbine Collector's Club - Page 1

Beware there's been some (Chinese made?) corrosive .30 carbine being sold as Lake City as recently as 2022. When in the box its obvious but the head stamp is not as easy to spot. THE CARTRIDGE COLLECTOR
That could cause a problem if not cleaned right away.

Some free digitized editions of the Ordnance Book are available on-line. Search for TM 9-1276

As an aside: Until the late 1950s the piston was not typically removed. Then it seems there was a policy change.
Piston Nut Staking - The Carbine Collector's Club

 

[DWalt]

The standard advice was to leave the piston alone due to the possibility of permanent damage to the housing. I have never removed one but I do have the nut wrench. I clean mine by holding the carbine muzzle up, plugging the bore with a wad of paper behind the vent hole, pouring some bore cleaner in, enough to cover the vent hole, then wiggling the piston back and forth using a magnet. That pumps the bore cleaner in and out of the housing. Then pour out the bore cleaner and remove the plug.

Some Chinese .30 C ammo did use corrosive Berdan primers. Tough to identify it, headstamp is LC 52, looks like Lake City production. There was also some Dominican Republic corrosive ammo imported. I have some. Could be some other foreign .30 C ammo with corrosive primers that I am unaware of.

 

[Patrick L]

I'm interpreting the OP as saying the piston is stuck in the housing on the barrel (stuck forward.)

I concur, penetrant and some gentle wiggling should free it. If not, ad Matt X suggested, reassemble and go to the range and fire it. That should knock it free, then disassemble, remove castle nut and you should be good.

 

[LostintheOzone]

I take it that both the piston and the retaining nut have been removed, but the piston will not separate from the nut? I have seen pistons get sticky, but not frozen in place. At one time, carbine parts used to be readily available, do not know the situation today. Heat might work. Also maybe a soak in penetrating oil.

Parts are still out there. CMP forum is a good place to find them. It's also a good place to find a solution to solve a problem like this one but I think it's been covered.

The nuts come loose. They used to stake them but no need to do that. Blue Loctite will save you.

 

[bruce381]

put nut back on do not cross thread and shoot it 40,000 psi hiting it should move it

 

[dfariswheel]

As posted above, Kroil is your friend.
Apply liberally and let soak a couple of days.

Don't get rowdy, new barrels aren't cheap or easy to get.

 

[Retired W4]

I have it soaking in Kroil since yesterday afternoon with the nut removed. If I can't get it out by tomorrow I will reassemble and shoot it as recommended above. Will report.

 

[Retired W4]

Piston was still stuck so I reassembled the carbine and fired one round. It functioned perfectly so I pulled the stock off and the piston is back to the stuck position (forward). Lots of oil, etc. in the cavity of the op rod but the piston still will not move freely. I'm back to soaking the piston in it's housing. I am reluctant to shoot it too much because I am confined to my basement/garage. I will take it to a shooting range to give it a real work out.

 

[Matt_X]

So if I understand correctly, when you fired it, it cycled properly and ejected the cartridge. But then on examination the piston was is still not easily moving back.



Consider joining the CC forum and see if there is further suggestions as there are pretty dedicated carbine guys there.
My experience has been that the piston is not easy to move, but usually I can move it with my fingers or a gentle tap on the wood bench with muzzle up will drop the piston back.



The piston surface is very smooth and precise and so doesn't take much to keep it from moving freely (like a suction forms) and still work fine under pressure.

 

[DWalt]

If the piston is stuck forward, I do not understand how it could function. But if it does, I wouldn't worry about it.

 

[Threadkiller]

I assume forward is the position the piston is forced into when the slide slams forward into battery.
When the gun is fired the piston cycles and then returns to its forward "stuck" position.
I would fire a few mags through it and then pull it out of the stock and see if the piston will move.

 

[gym cat]

Kroll oil soak -- and patience !!!!!!!!!!!

 

[Matt_X]

I don't know if this helps, but here's a photo of a piston after a session at the range. Either 35 rounds (match) or around 70 if it was practice. Would need to check my notes, but the exhaust residue is quickly evident regardless, although I've never looked after just one round.


The same carbine's piston and nut when clean show evidence that it was removed and restaked at some point. (It's a Saginaw Gear that someone basically 'restored' to WW2 configuration)

 

[ColbyBruce]

Retired W4 holler if you need to borrow a heat gun.