M14 Forum banner

Increasing headspace

3007 Views 24 Replies 10 Participants Last post by  sdayton
I know there are a couple of gunsmiths who frequent here and I have a question about tight headspace. I had a Poly rebuilt and had a new H&R chrome lined barrel installed and GI bolt. After getting it home, I checked the headspace with forrester .308 gauges. It closes on the Go gauge. I estimate it at, or just over 1.630 whichh is a little tight for my liking. I only shoot surplus, Port, Radway, SA. With the bolt stripped, it will not close on any of these rounds with finger pressure. I know Fulton has on their page that the spring pressure will close the bolt, but I think it is to tight. I have tried 2 other GI bolts, which 1 is a new winchester and the other a slightly used TRW and both were even tighter, so no good there. Is there a way to increase this headspace to about 1.633 or so? I don't think lapping the front of the lugs will help, but I don't know. These are all the bolts I have to try, so I don't know what to do? I emailed the smith who changed out the barrel, but have not heard back from him yet, but will soon. Let me know if you guy's have any ideas, Thanks.
1 - 20 of 25 Posts
The M14 should close on a SAAMI NO-GO gage. Got one?

Looking at the bolt I'd guess lapping the rear of the bolt lugs would increase headspace. Lapping the front just makes the bolt loose.

There's no safety issues here, but there could be stoppages.

-- Chuck
All that surplus ammo you mention is sold as .308 Wincheser, not 7.62mm NATO anyway.

-- Chuck
The surplus ammo is 7.62 x51, not .308, I don't care how the importer marked the outside of the box. Either way, the bolt will not close on most of it with finger pressure. I have the GO, NO GO and Field for .308. It clloses on the GO, but will not close on NO GO. I put a piece of scotch tape on the GO, and it would not close on it. It is to tight and I am trying to figure the best way to increase it a little, any ideas? Or should it be rebarreled? I really don't want to go that route unless I have to, I just had the new H&R put on, but I don't want that tight of a headspace. I had an SA inc with 1.631 and had all sorts of FTE and I don't want this problem again.
Redbone you are correct on the ammo both the
FNM marked Port and the RG marked Rad is NATO marked
7.62x51, the SA is in all account is.308, but no matter because
I agree that 1.630 is too tight. I think there is a special reamer
for chrome chambers but, they are very expensive and, not
many 'smiths have them. Just going to have to e-mail around
and see if any of them do. Perhaps WARBIRD might shed
some leads on this. I like my headspace set @1.634 but 1.6335
is very good for accuracy.
Shops like Smith Enterprise have several bolts which they swap out to get headspace the way you want it. I'm using a HRA bolt and barrel, but in a Springfield Inc rceiver and it almost closes on a SAAMI FIELD gage -- meaning it's tighter than M14 NO-GO specs.

I think I'd lap the bolt rather than the receiver.

-- Chuck
If you don't have any good shops around then I would suggest going to the next show around your area and trying a bunch of the worn looking bolts if anyone has them and finding one to your satisfaction.
I wouldn't lap it or anything unless it is necessary. If you have already fired it before the barrel change then it probably isn't.
FWIW, my norinco is even tighter than yours with this douglas heavy barrel I got on it right now and the H&R it came with was about the same as yours. I have the same bolt as you too. I have shot many many thousands of handloads and a very few surplus rounds through it and headspace has never grown. Not anything measureable anyway. If I were you I would be happy with it and get into handloading. It sounds like yours is very similar to mine the way it was when I got it and with handloads you can't even immagine how accurate it is capable of being. I say handloads because you can size them to fit your chamber. Have you ever thought about getting into it? You got the perfect rifle to begin with.
See less See more
I will try the show to see if I can find any decent, worn bolts. I really don't want to get into handloading. I don't really have the time or money to put into it the way I would want to. With surplus being as cheap and accurate as it is, I can't see loading right now. I first had a SA inc. NM barrel on it, but it started to get these weird lines or scpaes in the chamber. It was not getting scratched by anything, just these lines were forming, two of them, you could feel them if you ran something inside the chamber. It was not the barrel I wanted anyway, so the smith put on The GI barrel when I eventually came across one. I like the whiole chrome lined barrel with surplus to shoot away with, cheap and will last a long time. Does anybody have a decent, bolt with somewhat worn lugs? the bolt must have a good boltface on it? let me know?
Is there any other way to increase headspace a tad?, Thanks.
Increase HS

Redbone: I have installed GI trw bolts in all three of my Polys. waterbased valve lapping compound will lap your bolt in. I put a fired cartridge in the chamber to plug the bore, and give the bolt something to push against. Strip the bolt, use a scratch awl in the extractor hole as a handle, apply compound to the lug surfaces (its messy) and work the bolt closed and open. It won't take long, keep checking often and it cleans up with HOT tap water. works for me Les
it shouldn't really matter the port, aussie, israeli, etc surplus that i have checked all gauge with sammi specs on case length. which mirrors what clint says on the fulton armory web page. so long as your rifle is over the minimum you should be good to go.

the extra length on military M14 chambers is to compensate for fouling and the heat on full auto.
Les Staley,
What grade of laping compound do you use? coarse, medium, fine or extra fine when you lap in a bolt.


If you have a chrome lined barrel,don't even think about using a chamber reamer on it.

The bolt has 2 lugs on it.

Safety lug on the left and locking lug on the right.Only lap the right lug to get a longer headspace.If you go to far you can ruin a bolt real quick.

Oxmix-use the fine stuff and watch it closely. :roll:

"open for business"

See less See more
TRW bolts were late contract and can be the tightest headspace. Folks routinely fit them to tighten headspace. Look for another HRT or SA marked bolt.

-- Chuck
Increasing Headspace

I used to maintain 40, M-14 rifles for the Va. State team and found the easiest way to increase headspace was to take about a 2" long piece of op rod spring, wrap one end with rubber tape. Place it into the chamber, taped end first. Strip the bolt, put the bolt and op rod in the rifle, apply lapping compound to both locking lugs and cycle the op rod as long as it takes to get 90 percent contact on both locking lugs. We also used this process for installing new barrels, the chamber was finished after lapping the bolt in. Sam
Something new

Warbird, Is this something new, I've been building these things for 20+yrs. and have never heard anyone advocate only lapping one locking lug. These things operate at a chamber pressure of between 50-62,000 PSI and this equates to about 18,000 lbs. of rearward force on the bolt. I for one want as much contact as possible on both locking lugs. This also prevents the banana effect on the cartridge case as written about in the 60's by Creighton Audette. Sam
Lapping bolt

Oxmix: I use permatex 34B, as bought at auto-parts store. All three of my Polys hs at 1.633, the same as my first M1A SA standard tag read. I've noticed no increase in hs, after shooting several hundred rounds. (I lapped both lugs, as I don't know how to do just one) best of luck, Les
Thanks for the info guy's. A couple more questions.

Do you need to cover all the areas you do not want to get the lapping compound on? The bolt that is in it is a USGI SA bolt, that is used, should I use a newer bolt to lap in, or does it matter? What about getting the compound in the chamber, a big NO-NO? What is the best compound to get and where? It sounds as if you put some on the lugs, work the bolt a little, clean off compound, check headspace and repeat if needed, correct? Do you need to put alot of pressure on the boly when cycling the bolt? I don't think it should be to much trouble, I only need to go about two thousandth's , Or is that alot, considering the area?Sorry for so many questions, just looking to do it right the first time, so I don't screw up a bolt, or worse the receiver. Thanks for the help guy's,
Lapping bolt

Redbone; Use a fired case in the chamber to plug it and it will put a little pressure rearward on the bolt face. Use the bolt that needs to be set back,as it is already close. Do you have no-go gauge? 1.634? keep checking as you stated in your post. You don't want it to close completely on the no-go. Check before you do any lapping and see where the gauge stops, then when you see any appreciable difference in the position of the bolt with the no-go g. in chamber, stop! You
're only trying for a thousandth or two... Les

Nope,nothing has changed.
I had 1 cup of coffee this morning and had 1 pot to go.

Here's the way I do it.
If I need say .005-.006 average to get the haedspace I need I do the right lug only,first.The left lug will stop you from going to far and found this to be faster.Then I'll do both.

That's because of the larger bearing surface on the right lug that takes longer to do when doing both at the same time from the start..After .003-.004 is taken off (if possible) I'll then do both lugs so they lock up at the same time.

If I only need say .001-.003 I'll do both at the same time.

I don't really tell folks how I do things since I make a living at this.But,I stuck my head out on this one. :mrgreen:

Fly high,shoot low and you'll hit'em every time.warbird
"open for business"

See less See more
Thanks guys, I should be fine, I don't need to take of much at all. I appreciate all the info.
1 - 20 of 25 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.