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headspace question

1887 Views 18 Replies 7 Participants Last post by  delloro
my new M14-type shoots Fed AE all day with no problems.

aussie and port need a bump on the op rod handle to go into battery most of the time. a bump on the back of the handle and it pops right in to battery and shoots that round just fine.

locks open on an empty mag every time.

USGI Chrome barrel, USGI bolt and oprod, new spring, action is still tight, and I only have 100 rds through it so far.

would short headspace cause that?

Thanks all
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Headspace sounds like a likely candidate here...the Nato surplus cartridges are probably longer...

The only way to know for sure is to measure your chamber headspace and individual cartridge headspace. Cartridge headspace should measure at least .002 less than chamber headspace...If this is the case, then headspace is probably not the problem. If cartridge headspace is longer than chamber headspace then that is a serious problem...worst case is an out of battery fire.

It would be interesting to check the Fed headspace while you are at it to see what is necessary in your rifle to achieve good functioning.

Have you greased it well and cleaned the chamber recently??? Might as well start with the simple fixes first.
yes, I meticulously cleaned everything. the bolt was disassembled, reparked, and reassembled. the chamber is spotless, and the gun is well greased.
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.

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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
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We were just the opposite in the navy. Grease everywhere. gooped on the spring and guide and the bolt and hammer, inside the back part of the receiver and the guides. THE ROLLER. It never failed for me. If it's too tight to operate with grease something is wrong with it. In the army a liberal hosing of clp was all that everyone else ever did to their M16's. I cleaned mine right and it worked but I can't say that for the others.
Does your new M14 type rifle have a USGI barrel or commercial. I would check to make sure op rod is not binding or bolt dragging. Go ahead and wipe the grease off if everything else posted above checks out. To much grease on bolt race ways will slop grease where you don't want it. If you have a USGI barrel the head space should be on the long side and not have a problem with a little grease or dirty chamber anyway. If you had someone build it for you, have them check it out. Something ain't right. The op rod should slam forward with more authority than you can give with the palm of your hand on the op rod handle. The M14 don't need no stinking forward assist! I hope you get it figured out quick. You should have no trouble with ball ammo.
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!
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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.

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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.


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


No, they do not. 7.62x51MM cartridges are fractionally larger than .308 commercial cartridges. A miniscule amount, but enough to make them dimensionally different. Jerry Kuhnhausen devotes pages of his shop manual to this very subject, and the confusion surrounding it. I do not know where you got that info Chuck, but it's factually wrong.

If you have a rifle that is chamber headspaced (with a component bolt) at the low end of commercial .308 range, like 1.630 - 1.631, it would be very foolish to try to shoot military surplus ammo through that rifle. You could end up with a slamfire, or at the very least, failure to fully lock up. Likewise a rifle with a chamber headspace at the high end of 7.62x51MM specs, 1.64-whatever, should not be used to shoot .308 commercial ammo. That could result in case head separation because of excessive chamber headspace.

Commercial .308 and military 7.62MM are dimensionally close but far enough apart that using the "wrong ammo" in the "wrong rifle" can be dangerous.


Your little problem is a head scratcher. Did your smith lap in the bolt to your receiver?

Just asking because from what you say about something on the left side throwing your bolt off center a bit just as it starts to close gives rise to the question of whether there is a burr or some type of high spot on that side where the receiver locking lug/bolt lug raceway is.

That possibly with milsurp ammo (having a slightly longer headspace) might hold the case head back a fraction so that the bolt lug hits this hypothetical high spot or burr, thereby making it necessary for an "assist" on the op rod to lock up.

With the commercial ammo having a fraction less cartridge headspace, the case head doesn't stick back/out as far from the breach, thus allowing the bolt lug to pass by the hypothetical burr or high spot before it is required to fully engage and lock the extractor on the head of the cartridge.

Just a thought. I hope it wasn't too rambling to follow.

Let us know what you find out...interesting.

You have some useful information now...good show...

You can let the issue of headspace rest for the moment, and come back to it later.

All commercial receivers need to have the bolts lapped in to achieve a minimum of 85% bolt lug engagement, and often need to be clearanced in other areas in order to achieve proper bolt fit/function. The bolt needs to close smoothly without any hitch. Bolt fitting is pretty critical and are not a drop in component.

Are you familiar with the use of Dykem Blue? That is the best way to find any areas of interference.

how am I supposed to see prussian blue on black parherizing????

OK, on closer inspection, when I close the bolt by pushing in and down on the roller, right after the bolt lug cams over the receiver lug, the left side of the bolt "nose" hits the barrel ever so slightly. can I relieve the shoulder of the bolt nose where it is contacting the barrel breech? I'm thinking of using some fine emery to tapet the nose a bit where it contacts the breech. what does Smith do when he fits a USGI bolt to a Chinese barrel and the bolt interferes with the breech? does he relieve the bolt?


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.
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Re: headspace

M14 LOVER said:

My other thought on your problem is;
Did this guy screw your barrel into the receiver too much?
no, it is indexed very very well.

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.

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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
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FWIW I compared my rifle with anothr and checked for the same bolt bind. It had a slight hitch when the bolt started to cam over and the bolt nose contacted the breech - but I could not get it to bind.

so I popped a winnie bolt in my receiver, and it would not bind. which sux 'cause my rifle is all HRA, but life ain't perfect, I guess.

next thing to do is go to the range and see how she runs, but that will have to wait 'till after deer season.

thanks again everybody
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