Look out! It's a newbie with carbine problems!

There are no GI parts on this one. I played mix-n-match with parts from a friend's Inland and everything seemed to fit. naturally, I gave him back all of his GI parts.

I polished the ramp last night. I also removed some of the welding and exposed the parting line between the piston nut and gas cylinder. Then, the little guy got a detailed cleaning and reassembly with proper lube. The Inland is going to come visit this afternoon and we'll make a run to the range for further evaluation.

I went to Fulton Armory's site and ordered a new piston, nut, wrench, op rod spring, spring guide, and a sling for the stock I have coming in.
When the parts arrive, I'll get the old piston out, dress the butchery on my mill, and install the new parts. I have the feeling it will straighten out. If not, I'll weigh my options. The above parts represent a small investment that can be applied to any GI spec carbine.

And you will learn alot about carbines in the process. Good choice sir.

I enjoy tinkering with mechanical things. That's why I've got a machine shop at home despite not being a mechinist for a living.

We took the carbines to an indoor range last night. It showed a couple failures to eject and failures to feed on each magazine fired. We swapped parts one at a time to see if it would help. We tried his bolt, recoil spring, guide rod, and magazines. It still exhibited the same issues.
When we got home I noticed that the gas cylinder was cracked on the bottom. It gave itself away by the gas residue on the gas cylinder. I notched the crack and welded it up with just enough heat for a good weld but without heating up the barrel. The welds were ground and polished without heating things up. After a thorough cleaning to get the metal, grinding, and polishing residue out of the carbine it was reassembled and put away for the night.

My shooting group had a range day this morning. I stopped in before work and ran a magazine full of Remington FMJ through the carbine. It had one bolt over base failure to feed on round 8 of 15.

When welding the gas cylinder I closed up about half of the vent. The piston is so chewed up that there is lots of extra gas getting around it. I hoped reducing the port would help put more gas on the piston and increase function. I can easily open it back up when the new piston and nut arrive.
Another thing that is rather annoying is the front sight is canted to the right. I can see that it's tight but not centered on the key. I'll knock the pin out and try lining it up better.

Again, I can futz around with this barrel's gas cylinder and not be too worried. I'm not weakening it structurally and if I can't get it to run I'll change the barrel. Unlike many butchers out there I have a clue what I'm messing with. My purpose in coming here was to find people that know more about carbines than I do. I don't have an ego and am not afraid to learn from others.

As it is, I'm having fun tinkering with the carbine. When I get it running I'll probably have to go back to wrenching on the hot rod to get my fix-it fix.

The part of the gas piston that works is inside so it is not buggerd up at all. The part you see is used to drive the slide back. It has no effect on the gas system.

If the sight is cocked to the right the barrel has been under tightened. Taking the front sight key or pin will not allow you to fix the problem.
Dave

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Originally Posted by feets

I hoped reducing the port would help put more gas on the piston and increase function. I can easily open it back up when the new piston and nut arrive.

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I don't follow your reasoning. Why would closing down the port put more gas behind the piston? Seems like such throttling would actually allow less gas into the chamber and so reduce the pison's "push".

I understand that the head of the piston lies behind the nut. It creates the seal. The portion passing through the nut is essentially a pushrod. It's been mutilated. I can't help but think it could be allowing the piston to tilt slightly, especially if the head is a loose fit in the non-GI barrel.
There's the whole thing about the missing mass too. That would cause the piston to react quicker but I'm not sure if it would have an appreciable impact of the force applied. Lighter bullets moving fast are easier to stop than heavy bullets moving slow. This whole train of thought may be getting too deep and may not make any difference in the operation of the rifle. Theories are wonderful but facts make the world go 'round. The new parts will be in next week so I was just playing with what I had to work with.

I keep reading the signs as too little movement on the op rod. There doesn't seem to be proper force pushing the slide rearward.
Closing the vent would put a little more push behind the piston. Considering the angle of the vent it looks like it would be exposed when the back of the piston passes it. This is pure speculation since I can only see threads on the nut behind it.
I did not weld it closed. That would mean being dangerously close to welding the threads of the nut to the cylinder. I closed most of the exit without filling the void underneath. That will not increase pressures dramatically. At most, it will increase the velocity of the gas exiting the port. Pressure behind it will increase slightly but is shouldn't be an appreciable amount. It's more of a split second timing kind of thing.

Cannons, I didn't close the hole in the barrel. I closed the vent that allows the gas to escape the cylinder after pushing on the piston. It vents from the gas block into the stock.

Collector, the sight is not in perfect alignment with the key. I imagine the barrel might be a degree or two off but I can see where the sight seemed to be a loose fit on the key until the pin was pressed in. Whipping up a little fixture to hold it in place while I reinstall the pin should be easy.

There is no hole that allows gas to escape. There is a drill hole used to drill through into the barrel. After that the nut's threads covers the hole. You can have a point about missing mass and if the end of the piston no longer square. I can not state how either would effect function. Might some or might not. Thoughts to ponder. If the piston was shortened it could affect slide speed the same as a gas port partally closed. I have seen gas ports not cleaned out with drill cuttings partly in them. Not lead but steel.

I guess I missed the point on the drill port. I was thinking it was an exhaust like I'd seen on some other actions.
Not a problem. It'll open up in a couple minutes of work.
Checking the gas port in the barrel would be a grand idea, don't you think? I kinda blew right past that one since I can't get the stinkin nut out.

I've tried all kinds of things to clean out the gas cylinder. Not being able to get the nut off puts a damper on the fun. I've sprayed my heavy duty action cleaner all around it multiple times as well as dumping Hoppes in there. I make sure the piston is all the way forward and hold the action muzzle down for that. After a good soak, I turn it muzzle up and fiddle with the piston. Whenever it pokes down the sides are covered is black nasties. Last night was the first time I was able to get it to move by tilting the action. Disturbing, eh? Most of the time I have to use a pair of pliers to rotate the piston and pull it rearward. There are some clockings of the piston that won't let it move rearward without a fight. No doubt that's killing the function. Granted, 40,000 psi in the chamber pushes harder than I can pull with pliers but if it's slowing down the works that can lead to FTEs and FTFs.
I just brought home $175 worth of dies, bullets, primers, and assorted items for the 30 carbine. I guess I'm in it for the long haul now. :super:

I'm going to the range tomorrow with my former armorer friend. If this was a 25mm Bushmaster cannon he could fix it right up but the little carbine pre-dates his service. Still, a day on the range is better than a day at the office. :D

I really can't understand why you're still fiddling around with that fubar'd barrel. The only way it could possibly be fixed so it would function properly is to replace the gas cylinder......providing the bore/barrel has'nt been ruined by being welded on multiple times. Welding on something that has to stay perfectly straight is no easy task, and it distorts the metal, causes warpage and changes it's structural integrity, not to mention putting it under loads of stress. Likely, the bore has a tight spot directly under the welded area or will be warped or both. Go with the original idea and rebarrel it or take everyone else's and scrap it and get one you don't have to worry about a barrel rupture on every time you pull the trigger. Theres a reason the originals have the gas cylinder swaged in place, IIRC Iver Jonnson and others silver soldered theirs on and thats the reason the weld cracked, impossible to weld over that stuff and get it to hold up. JMHO