headspace question

Here is another simple test you can try right away...if you don't have all the guages handy to determine the true headspace of your rifle...

Disassemble the bolt and put it back into the rifle stripped. Then insert the surplus cartridges into the chamber one by one, and slowly see if the bolt will go all the way into battery using a very light finger touch. See if you can feel any resistance to the last 1/4 inch or so of locking lug turning movement.

Separate and mark the rounds that close without resistance from the ones that don't ...if any. The ones that close are ok to shoot in your rifle. The ones that don't are too long.

The value of this exercise is to see if any of the cartridges you have are too long for the chamber in order to confirm, or eliminate headspace issues as the cause of your problem.

The final test is to fire the rounds in the ok pile to see if they cause any jams. If not, fire some of the other ones and see how they function.

The results of this simple test should provide some useful information.

TC

M14 type? Gotta have a brand name, what is it?

Sounds like excessive friction from new or out of spec parts, or grease used where oil should have been used. Either will slow the action. Could also be a weak action spring.

7.62mm NATO and .308 Winchester cartridges have identical external measurements and the bolt closes with a bit of forward assist.

Hit the shiny spots on the action with CLP.

Check the magazine lips for contact with the bolt. Are these USGI?

Get rid of the grease everywhere on the rifle other than sparingly where needed on the bolt, or clean all the grease off and use LSA -- during two years of daily carry of the M14 we never, ever used grease on them nor was grease available.

-- Chuck

Armscorp receiver, like new USGI H&R barrel, new spring, everything is clean.

I had a local gunsmith install and headspace the barrel. He does a fair amount of M14 work and is familiar with them. I gave him four bolts. He said 2 headspaced OK, the other 2 were dangerous to use.

I assembled the rifle myself. The op rod was tight when going into battery, so I stoned it a little. The rifle then passed the "tilt test."

With no ammo in the gun, the gun cycles manually just as it should.

The only thing I am not satisfied with is the stacking of the op rod spring I feel as I draw the charging handle all the way back.

FWIW, when I received the receiver, I screwed the barrel in by hand and it had too much "draw" according to Kuhnhausen's manual. I didn't say anything to the gunsmith, but they told me they had to remove a bit from the barrel shoulder to get the barrel to headspace correctly. That seemed correct to me. The barrel is indexed very straight; with the rear sight in the middle, and the front sight centered, I am an inch to the right at 100 yds.

When I dropped off the barrel and receiver, I asked where he would headspace it, and he said at the lower end of SAAMI 0.308 specs, and that mil surp would not work. I told him I intended to shoot mil surp, and he said he could set the headspace at the lower end of NATO specs and the higher end of SAAMI specs, IOW close on the SAMMI no go, but not on the NATO no go gauge, and that all ammo would thus work.

I don't know if the barrel is set too far back or not, as the bolt still has a little fore-and-aft movement when in battery (and unloaded); the bolt is not being held back by the breech. However, the other bolt that headspaces correctly, while it will go into battery with light finger pressure(op rod removed, bolt disassembled) there is no perceptible fore-and-aft play. That seems a bit tight to me.

because the rifle ran right through a box of Fed AE without a hitch, but hangs up with Aussie and Port, I suspect it is a headspace issue. Again, the rifle is meticulously clean, and lightly greased all over (except the chamber and areas that would foul the chamber) with plastilube, but certainly not slathered with goop. The rifle locks open on the last round, and it's not much of a bump needed to get it all the way into battery with mil surp, in fact, the hammer will do it (though the rifle will not fire, as it should not).

I don't have headspace gauges for 0.308.

I guess I'll have to improvise as suggested - strip the bolt, and feed in various types of ammo to see which chamber fully without too much effort, and which don't.

That and/or find another gunsmith with the right gauges and the time. The guy who barreled my action has a two-week waiting list....

Thanks all, and keep the info coming!

From all of the excellent advice you are receiving here, you can see that there could be several potential areas to look at to determine the cause of your problem.

However, since headspace was your first concern, it would be logical for you to take a closer look at it first, so that you can see if the problem lies there, or so that you can eliminate it from the list of potential candidates. Either result will contribute a lot to the troubleshooting process.

It's a prime candidate here because your rifle functions fine with .308 ammo, and 7.62 surplus is not made to the same specs as .308 commercial ammo. As a general guideline, if you were to actually measure 100 rounds of each, the .308 will average out to be shorter, and with less variation in length. Individual Nato spec rounds can be found that are .005 longer than average .308 lengths, and still be within Nato specs. There can be other dimensional differences as well, but let's look at cartridge headspace length first.

It sounds like your chamber headspace is likely within spec, but we are not trying to determine what the chamber headspace actually is; we are trying to determine if cartridge headspace is causing some interference with chambering.

It sounds like your gunsmith did a good job in setting up the rifle for you, but there is no harm in verifying his work. Many new builds will need a little fine tuning to get them to work, (even SA, Inc. rifles sometimes need a little tlc). And don't forget that they sometimes need a little break in as well.

Let us know the results of the cartridge/chambering test.

TC

update

I tried 10 rds each of fed AE, PMC commercial ball, port, SB, and even The Dreaded Wolf into the chamber with a stripped bolt.

all closed with light finger pressure, save one SB which was just a little sticky.

dagnabbit

I was able to make the bolt bind at the same point where it was not closing when firing. there is a small hitch to the bolt movement that can become a bind with the right (wrong?) finger pressure.

looks like I have to make the bolt work with the receiver.

anybody seen this with armscorp receivers before? the bolt binds *just* as it begins to rotate. it appears to be binding somewhere with the left lug (away from the roller). there are not any shiny spots to indicate where that I could see last night, but my lighting was less than ideal.

thanks again

headspace

delloro,

My other thought on your problem is;
Did this guy screw your barrel into the receiver too much?

I mean from what you say now, you know those relief cuts in the barrel breech are supposed to be in a certain line with the axis of the receiver.

When the bolt locks closed, the barrel breech shouldn't tilt the bolt out of line, it should stay perfectly straight as it rotates closed & locked. If the relief cut in the breech of the barrel is off where it is supposed to be in relation to a closed bolt IE; the extractor snapping over the case head, that could cause the bolt to tilt off axis.

Are the gas cylinder & flash hider splines perfectly straight, or are they rotated slightly?

It wouldn't take much to mess it up.

Delloro,

Prussian blue is a type of bluing product I believe, the Dykem Blue I am referring to is a liquid coating that when applied to metal will scrape off in the contact areas...it is available at machine shops or Brownells and is used to determine clearance in tight fitting parts.

You will have no problem seeing it clearly on the parkerized parts, especially the locking lugs. If they have not been lapped to achieve 85% even contact, now may be the time, depending on your headspace. Ask your gunsmith if he did that already.

If I understand your description correctly, the nose of the bolt may contact the side of the barrel hood with manual manipulation of the stripped bolt...but it should be more centered in normal functioning by the op-rod with a round being chambered and the extractor installed.

If the receiver lugs are uneven, it could cause the same symptom.

It sounds like you are on the right track though...you can safely polish 1-2 thousandths from the bolt hood to achieve good function...but I would not use emery paper, I would use 600 grit wet paper or a fine arkansas stone.... and I would really want to make sure that I had correctly analyzed how that bolt were locking up before I made any mods, to insure that I had addressed the underlying geometry issues.

TC

In point of fact- .308 Winchester and 7.62x51 cartridges are exactly the same. What differs is the chamber. .308 Winchester chambers are 1.630 to 1.640. Wheras 7.62x51 chambers are, as I recall ,1.6315 to 1.6415. The same type situation exists with the .223 and 5.56x45. The lengthier chambers reflect the military's thinking on crud on the battlefield. The other difference is concerning pressure. The .308 is loaded to higher pressure than the 7.62x51 while the converse is true of the 5.56 vs. the .223. In this instance the military load is hotter. For those that disbelieve, simply buy a cartridge headspace gage and check a few. And then check the ballistic charts re. pressure. Where some are lead astray on the headspace issue, is the fact that makers of ammunition use varying tolerances. Or in the case of Indian ammunition, make up the tolerances as they go. Before I posted, I measured 5 each of Remington factory ammunition and 5 rounds of Portuguese surplus. The Port went 1.6295 to 1.6320. The Remington went 1.6315 to 1.6330. For these ten cases that means that the commercial ammunition was longer than the surplus. The Wilson cartridge gage was checked versus Forster headspace gages. They checked out dead to each other. The actual headspace of the cartridge was checked with an indicator while in the cartridge gage. Another interesting fact is that while a cartridge can be as long as 1.640 or even 1.6415, a chamber can be as short as 1.630. The cartridga and chamber would both be in spec. Another reason why the military allows longer chambers