M1 .30 Carbine won't chamber because barrel threaded too far in?


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U.S.SFC_RET
November 13, 2006, 08:06 PM
I posted this over on the firing line but no one is picking up on it so I will post it here,
I picked up a winchester M1 .30 cal Carbine that I have experienced shooting problems and noticed when I chambered a round the locking lugs wouldn't lock into place. I used a vernier caliper and measured the round just to be sure and the round was well within specification for length. Question I have is this, I know that you can back the barrel out to increase headspace but is this proper procedure? Or is proper prodedure to ream out the chamber? I would suspect if you back out the barrel the barrel would be loose and you would need shim the barrel. On the other hand to ream out the chamber to exacting headspace tolerances would allow you to run the barrel down to practially deadstop into the receiver. Which direction do I take?

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gamachinist
November 14, 2006, 12:08 AM
Backing the barrel out one turn will make the headspace excessivly long,and would make the barrel loose and wobbly.

The only proper fix is to rebarrel with a barrel that headspaces correctly or to ream the chamber on the existing barrel.

Someone may have put that gun together out of parts and never checked the headspace.Someone may have swapped bolts also to get a matching manf and style of bolt to make it "correct" and caused the short chamber condition.

There have been reports of CMP Springfields that had new barrels installed and never reamed for correct headspace.
Perhaps there are some M1 Carbines out there with the same problem?

I would recomend you buy a "go" headspace gauge and check it yourself,or take it to a gunsmith who has the proper gauge and have him check it before you do anything.

Is the barrel marked with a manf id and date behind the front sight?

Firehand
November 14, 2006, 01:21 AM
Yeah, with that barrel sounds like the chamber is a bit short. Only way to fix that is to cut it deeper with a chambering reamer.

Sunray
November 14, 2006, 01:44 AM
Start with headspace guages. Then check the cases for length. A chamber cast will tell you if the chamber is correct. Cerrosafe from Brownells. Mind you, if the cases are the right length, I'd almost bet that some twit installed the barrel without knowing how. You can't back the barrel out, but it could be machined to shorten the threads a tick and rechamber.

georgeduz
November 14, 2006, 02:02 AM
I had one years ago,it did the same thing.and it was the gas piston that was broken and would not allow the bolt to come foward and lock into place.it worked just fine after a new piston,what a fun little rifle that was.

U.S.SFC_RET
November 14, 2006, 07:50 AM
This barrel has not been reamed to accept .30 cal carbine rounds to chamber. It is an unused winchester barrel. bullet has been miked. Gas piston OK. I cannot shorten the threads the headspace is too short becuse the chamber has not been reamed.

Jim K
November 14, 2006, 05:19 PM
Hi, US SFC_RET,

DON'T MESS WITH THE THREADS!

It looks like you or someone put on a new barrel, not knowing that new barrels are short chambered so the headspace can be adjusted after installation. You need to ream the chamber, checking to make sure you are good with the GO gauge. As soon as you are OK with the GO gauge, that's it. You can check with the NO-GO also, but you don't need to if you did a proper "cut and try" reaming.

Jim

U.S.SFC_RET
November 14, 2006, 07:49 PM
Riger Jim I am kinda wonderin If I can rent a pull thru reamer and use the bolt and when the bolt locks up.. Pop goes the weasel!
Also it looke to me that the unfinished barrel looks to have a 90 degree squared off lip of sorts. looks not reamed to me. If that's the case than I've got options like closer head space if I want it. :D

gamachinist
November 14, 2006, 09:26 PM
That's exactly what you need to do U.S.SFC_RET .

Check with member KenD and see if he has one to rent.

Jim K
November 14, 2006, 10:05 PM
If that 90 degree "lip" is at the front of the chamber, it is correct, it just needs to be moved out a tad. The .30 carbine cartridge (like the .45ACP, 9mm Luger, etc.) is supported (headspaced) on the case mouth, so there needs to be a sharp shoulder for the case mouth to fit up against.

Jim

Gun Plumber
November 17, 2006, 12:29 PM
Call the folks at Fulton Armory and talk to them. They will have several specific questions regarding YOUR M1. They will also have all the parts you need AND can do the work if you don't feel comfortable doing it yourself.

This is one of those things that MUST be correct or you can injure yourself and anyone around you when (if) the receiver grenades itself. Not saying it will, but with an improperly headspaced round, you do expose yourself to extreme pressures than injure or kill you or those around you. Never a good prospect.

http://www.fulton-armory.com/M1Carbine.htm

1911Tuner
November 17, 2006, 01:35 PM
Good advice given by all, but I'd like to add a few points if I may.

Reaming the chamber a little too deep from where it stands won't make for excessive headspace of the ka-boom variety. That's determined by the amount of breechblock setback when the gun fires. If that's within allowable tolerance, it's okay. If the headspace is excessive IN the kaboom direction when you get it reamed, it was already that way before you started.

The mechanics are thus:

On firing, the breechblock...bolt...is thrust rearward under pressure, and...if the dimensions allow the bolt to move backward, the breech opens by that amount and the case follows it if it's a straight-walled case. Or...if it's a bottlenecked case...it stretches ahead of the web and the head moves rearward until the rim stops against the bolt. If the straight-walled case loses enough head support, it bulges or blows out. If the bottleneck case stretches far enough to exceed the elastic limit of the brass, it produces the tell-tale "Ring Around the Case Wall" of incipient head separation. At that point, you're within a few tiny thousandths of catastrophic head separation.
This category of excessive headspace is determined by the bolt and its locking recesses in the receiver rather than by the chamber stop shoulder.

Since there's obviously something wrong with the way the rifle was assembled, it would be wise to have it inspected by an armorer or gunsmith so that a determination can be made as to whether or not the rifle is safe to fire with the bolt that's in it, regardless of what the gauges show.

Luck! The War Baby is a fun little critter to shoot.

U.S.SFC_RET
November 18, 2006, 06:11 PM
I used a pull through reamer with the bolt face closing on the reamer. Reamed and reamed some more and the bolt closed. Just like Tuner said if it goes kaboom it woulda went because the bolt wasn't closing. Let me tell you it is nothing but a miracle that I or no one else got injured the fired 45 rounds through that thing. I have no Idea how I didn't. I have all of the expended cases and they all look fine, no splits or bulges.

1911Tuner
November 18, 2006, 07:08 PM
If it was that far out of battery, it shouldn't have fired at all.:confused:

gamachinist
November 18, 2006, 10:09 PM
That's what I'm thinking also Tuner.

I wonder if there is a problem with the firing pin being too long or something else that should prevent it firing?

1911Tuner
November 18, 2006, 10:31 PM
gamachinist...possible, but even so, the hammer shouldn't fall after a certain point out of battery. Depends on how far. This would be one of those I'd have to see in the wood and steel. Not as good with long-distance diagnosis on the War Baby. Other than assembling a few over the years...and haven't done so in about 20...I can't remember a lot about'em.


U.S.SFC...Take a close look at the rear faces of the bolt lugs for any sign of damage.

U.S.SFC_RET
November 23, 2006, 09:44 AM
The rear locking lug faces look good and flat with the exception for the top edge of the left locking lug, just a bit of wear at the corner. When I reamed the bolt into place the locking lugs mated right in like they were meant to be. The rear faces of both lugs are nice and flat, smooth faces. The bolt is correct for the gun. The bolt face itself looks good where it meets the primer. The bolt locks up nice and tight.

1911Tuner
November 23, 2006, 10:09 AM
Good sign, but still no guarantee of safe headspace. The lugs may be worn instead of battered. Study this for a minute until you can see it in your mind's eye.

If the locking lugs are worn on the rear faces or the lugs and their recesses are dimensioned so that the bolt will sit farther to the rear than spec...you can have an unsafe condition even though the NO GO gauge indicates good headspace. Bolting on the GO and not on the NO GO only means that the linear dimension from the boltface to the stop shoulder is within allowable tolerance. There are other things to consider.

When the bolt is able to move farther rerward than spec...even with the gauges showing minimum linear dimension...the case is unsupported by that amount because the case isn't sitting deep enough in the barrel chamber...
even though the bolt will barely go to battery.

A hypothetical may help:

Take a new barrel without a chamber. Ream and finish the chamber .025 inch short. The bolt will refuse to go to battery on the GO gauge, indicating
insufficient headspace. The way to correct it is, of course...to ream the chamber deeper. If...on the other hand...you remove .025 inch of material from the rear faces of the bolt's lugs...the GO gauge will go to battery, but you now have .025 inch of the case head unsupported. When the pressure hits, you get bulged or blown cases.

Take the measurements on the cartridge case diameters at the web area, and note the average. Fire the rounds and measure again. If the heads have expanded more than about .001 inch, they're unsupported. Look closely for any bulging ahead of the web. If that bulge is more than about .002-.003 inch, you still may have a problem.

U.S.SFC_RET
November 23, 2006, 03:14 PM
Tuner I got it. What you are saying is that even though I reamed out the new barrel I have to look out for excessive wear at the rear of the lugs. I have to ensure that the case is supported by the chamber. No support at the chamber means excessive swelling at the web area of the case. This web area of the case is the thin area just past the base of the cartridge. Tuner I will measure the old cartridges to tell me anything that happened before. In the meantime I need to reasearch the specs on bolt lugs and micrometer them for length as well. I am in no hurry to fire this thing, especially when I lost that teeny little piece that sits on the end of the extractor spring because I didn't buy the bolt tool.

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