M14 headspacing: quick, simple, cheap, and pretty darned accurate - M14 Forum

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M14 headspacing: quick, simple, cheap, and pretty darned accurate

This is a discussion on M14 headspacing: quick, simple, cheap, and pretty darned accurate within the Gunsmithing forums, part of the M14 M1A Forum category; OK, head spacing an M14 rifle is NOT rocket science. While you could invest HUNDREDS of dollars for a complete set of .308 gages ranging ...


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Old May 7th, 2011, 11:50 AM   #1
Lifer
 
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M14 headspacing: quick, simple, cheap, and pretty darned accurate

OK,
head spacing an M14 rifle is NOT rocket science.

While you could invest HUNDREDS of dollars for a complete set of .308 gages ranging from .308 GO up at .001" intervals to infinity,
if you didn't know what you were doing with the M14 platform,
you could still have "head spacing" issues.

All you really need to head space one M14 at a time is ONE and ONLY one commercial .308 GO gage, 1.630",
a set of automotive feeler gages,
AND the proper procedures.


If you can find one, and if you are doing a LOT of M14 head spacing, you might want to also have a US GI military 7.62 NATO head space gage...
Military # 7274780B GI "GAGE HEADSPACE" for 7.62 NATO GO: 1.6355" This gage is also very close to a SAMMI .308 NO GO gage, and has the desirable ejector cut out relief slot.

First of all,
WHAT GAGE ARE YOU USING???
HOW IS IT MARKED FOR LENGTH??

Commercial .308 head space gages, like you get from Brownell's, generally DO NOT have a relief cutout for the ejector??? A genuine US GI headspace gage will have an ejector relief cutout.
which allows quick and dirty armorer inspection of head space on many rifles at a time, WITHOUT having to strip the bolt.

Second,
did you strip your bolt before checking head space??
With a complete/assembled bolt, the ejector will be pressing against the back of the uncut/commercial gage with tremendous spring pressure. No way you can get reliable head space measurements with that combination.

Third,
Have you checked your bolt lugs to see if the wear pattern indicates EVEN and adequate lug engagement??
On the M14, bolt lug engagement [ especially at the tiny left lug ]is a critical component of head space ...
on the M14 head spacing is NOT JUST A NUMBER.

Once you determine which gage you are using,
and if using a commercial gage, once you strip the bolt,
and once you decide that bolt lug wear is even,
there is a simple method to determine total head space on an M14.

With the gage in a CLEAN chamber,
with the bolt closed [ and the right lug fully down in the slot ],
use a set a automotive feeler gages to get the exact distance left between the rear of the right bolt lug and the front of the right receiver lug.

Add the feeler gage thickness to your gage number, and you have the exact heads pace for that bolt/receiver combination ...ONLY FOR THE RIGHT LUG.

Remember,
I asked you to check for EVEN lug wear before starting??

If the lug wear is even,
then we can ASSUME that the bolt is straight to the bore,
and therefor,
that the left lug clearances will be near identical with the number we came up with for the right lug.

VOILA ... M14 Head Spacing 101
zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

PS: here in Canuckistan, we have thousands of Chinese M14 clones with "generous" head space. On my personal Chinese M14 rifles [ when I say "personal" I mean those rare M14 rifles that stick around for more than A MONTH ] if I intend on target shooting, or for use with .308 Win ammo, I usually just lap in a GI bolt. 1.632" is the ideal head space I aim for.

So far, we have had a few reported M14 too-long-headspace case separation KABOOMS" , but to date, to my knowledge, all this type of KABOOMS reported were with reloads. The M14, especially one with long head space, is a fussy platform to reload for. Personally, most of my M14 reloads are done with thicker/stronger 7.62 NATO brass.

We have also had a few reported KABOOMS from other causes, mostly timing/firing pin stuck/hammer follow = out of battery KABOOMS.

In my experience with the M14 platform, the long head space issue is less of a problem, in terms of frequency and severity, than the out of battery KABOOM.

If you want to learn more about the M14, Inspection, Repair, Maintenance, and Modifications, check out my posting @:
http://www.m14.ca/seminar/M14_Seminar_EBR.pdf

Thanks from fatelvis, GARRARD, mspben and 6 others
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Old June 25th, 2011, 10:12 AM   #2
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And for the new guys to the board, an explanation of just what headspace is all about:

http://www.surplusrifle.com/shooting...pace/index.asp

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Old June 25th, 2011, 10:37 AM   #3
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Mass Inertial Confusion! Squared!

Excellent HS summary. MJ! Thanks! But now, let's have an equally simple summary of the Coriolis effect on long-range [>> 1000 m] accuracy:

To wit, and simplified:

"The Coriolis effect is caused by the rotation of the Earth and the inertia of the mass experiencing the effect. Newton's laws of motion govern the motion of an object in a (non accelerating) inertial frame of reference. When Newton's laws are transformed to a rotating frame of reference, the Coriolis and centrifugal forces appear. Both forces are proportional to the mass of the object. (NOTE: well of course they are! What else would you expect?)

The Coriolis force is proportional to the rotation rate and the centrifugal force is proportional to its square. The Coriolis force acts in a direction perpendicular to the rotation axis and to the velocity of the body in the rotating frame and is proportional to the object's speed in the rotating frame."


Yah mean, perpendicular to the left, or is it the right..., side of my M1A's NM sights?

Blah blah blah. And... when this topic is coupled with the general mis-understandings of HeadSpace, Whaddah Yah Get?

Why....

Mass Inertial Confusion is what! MIC! MIC!

Be Afraid. Be Very Much Afraid!

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Old June 29th, 2011, 10:27 AM   #4
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Good post live saving subject too.

Checking the headspace is it important or not????? You deceide..........


I been collecting and shooting the surplus military rifles for almost two decades. Checking the headspace is very important on any surplus military rifle or any rifle before we shoot it to besure its safe to shoot. I figured when i was new to this i wanted to avoid the scary horror stories about the mags being blown out and stockssplitting in half with some surplus guns. I read about out of battery firings and cases splitting is something i don't want to personally witness. Right away i purchased the headspace field gauges for all my calibers first. Then a little at a time checking the headspaces and it passing on the field gauges I wanted to know just how safe the chambers really are so i purchased the no go gauges next. I'm thinking checking the field head space and having them pass it just wan't enough for me. So i have the no-go gauges too now. With the rifles i change the barrels on i have the go gauges too. My point is little by little i'll have them all. I can't put a price on safety and knowing i'm safe when i pull the trigger too.

I had one rifle that I had a very bad gutt feeling about before i shot it. Something told me not to shoot it. It was a french mas m36 that century arms rechambed from 7,5mm french to 308win. One of there ufix'em's. I checked it with the 308win field headspace gauge and she failed. It raised my interest even more to see what mistake was made when they rereamed it. I purchased the 7,62nato field headspace gauge and it failed on that one too. I know there gunsmith/meat cutter went way too deep with the reamer. Just for ha's ha's I put .060'' on the nato field headspace gauge and it still failed. So it needs a new barrel or a rechamber again. This is one gun out of hundreds that i have checked for others too. If i shot it without checking it who knows what would of happened. The cost of the proper headspace gauge isn't worth the pain and suffering we can have if we didn't check the headspace.

If we like guns we can live and enjoy then if we check the headspace before we shoot them so were sure there safe to shoot. The cost of the headspace gauges can be the cost of one gun which money is nothing when it comes to our safety right??

Sorry but being safe but its number 1 to me so do it right, Godbless; Bill

BTW; A lot of gun guys are afraid of the old war horses but if we check them out correctly and make sure there safe to shoot the'll give us many years of shooting pleasure. I don't believe in wall hangers, guns are made to shoot in most cases.

Being new to my norinco m14 i checked the headspace with the 7,62 nato headspace gauge first and the bolt won't close on it. Then i seen stamped on the under side of the barrel 308cal. in very small numbers and letters So i got out my 308win field headspace gauge and the bolt won't close on that one too. Next i'll check it with the 308win go and no go headspace gauges to make sure the chamber is deep enough and safe to shoot. I'm new to this m1a/m14 thing and the barrel is marked 308cal while some say its a 7,62nato. So really what is it?? Is it 308win? or 7,62nato? Its a norinco sporter m14.


Last edited by BigBill; June 29th, 2011 at 10:44 AM.
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Old July 13th, 2011, 10:41 PM   #5
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I'm a member of the Fifty Caliber Shooters association and in the last two years we have had two shooter have a "Out of battery" detonations, both shooters were severely injured. One lost a eye and had a hole blown in to his chest, the other was a little luckier but his thumb was almost tore off. Both of these happened as the shooter was closing the bolt, not a head space problem, I'm just posting this to help people understand that these are not toys we play with and any thing can happen.

Casey

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Old July 14th, 2011, 08:52 AM   #6
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Quote:
Originally Posted by Earthquake View Post
I'm a member of the Fifty Caliber Shooters association and in the last two years we have had two shooter have a "Out of battery" detonations, both shooters were severely injured. One lost a eye and had a hole blown in to his chest, the other was a little luckier but his thumb was almost tore off. Both of these happened as the shooter was closing the bolt, not a head space problem, I'm just posting this to help people understand that these are not toys we play with and any thing can happen.

Casey
These detonations were with .50 calibre, right?

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Old July 14th, 2011, 02:05 PM   #7
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Yes, these were .50 BMG target loads, most likely 750 to 800 grain bullets with around 230gns of powder maybe as high as 250 gns.
I load 750gns Hornady A-Max bullets with 227 gns. of H50BMG powder [about 2600 fps] when I shoot at 1000yds.

Casey

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Old July 14th, 2011, 05:28 PM   #8
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Quote:
Originally Posted by Earthquake View Post
Sweets
Yes, these were .50 BMG target loads, most likely 750 to 800 grain bullets with around 230gns of powder maybe as high as 250 gns.
I load 750gns Hornady A-Max bullets with 227 gns. of H50BMG powder [about 2600 fps] when I shoot at 1000yds.

Casey
That sounds like a LOT of fun, except for the explosions part. If I'd been there, I expect I'd now be having a major flinching problem....

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Old July 15th, 2011, 09:11 AM   #9
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Quote:
Originally Posted by Earthquake View Post
I'm a member of the Fifty Caliber Shooters association and in the last two years we have had two shooter have a "Out of battery" detonations, both shooters were severely injured. One lost a eye and had a hole blown in to his chest, the other was a little luckier but his thumb was almost tore off. Both of these happened as the shooter was closing the bolt,
Were these semi-autos or bolt actions?

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Old July 15th, 2011, 02:15 PM   #10
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These were bolt guns.

Casey

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Old October 5th, 2013, 05:56 PM   #11
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Today I received my Clymer head space gauge. I removed bolt and tore it down, after chasing my ejector around I made sure everything was clean. I put in the .308 gauge listed as 1.630 and closed the bolt. using your method with automotive feeler gauges I could fit the .008 gauge but not the .009. If I am reading this right my head space is1.638 which is .002 under max for saami.

Now when I reload, do I not set the shoulder back as far so I'm not stressing the brass?

Also today I received my Wison case gauge for .308 and my reloads are a little long. Is it safe to leave them long for my firearm?

I have an early 90's Polytech with about 500 rounds through it.

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