my first is at the smith having barrel installed and bolt headspaced. If I understand correctly, the headspace should be between 1.630 and 1.634, both numbers inclusive. Am I correct? Thanks, Taz
I'm not sure why these numbers keep coming up (actually I do know...), but if you expect the rifle to function you need to use the M14 gages, not SAAMI bolt gun ".308" gages.
Do not expect your rifle to function well if it gages between 1.630"-1.634," although it might.
GO is 1.6350". Note GO is minimum chamber size. This is right about the same as a .308 bolt gun SAAMI NO-GO gage which is 1.634". So a M14 rifle should swollow a SAMMI NO-GO gage.
NO-GO is 1.6405". Note NO-GO is merely the maximum a new barrel, bolt, and receiver should read for maximum rifle life. It has no other significance. Once you fire the rifle it is no longer expected to meet NO-GO specs, although it'd be nice if it did. A .308 bolt gun SAAMI FIELD (reject) gage is 1.638" so you can use it as a tight NO-GO gage, although it's still too small. It's OK if it swollows a SAAMI FIELD gage.
FIELD (Reject) gage, part number 7274790, is 1.6455". Where to get one I've no clue. Bill Ricca could sell a boxcar load of them right here!
If your rifle swollows a SAAMI .308 NO-GO gage and "almost swollows" a SAAMI FIELD gage you're in darn near perfect spec. Don't let someone try to sell you a "short" bolt because the SAAMI NO-GO gage drops right in!
This has been discussed at length in an ealier thread.
1.630-1.634 "is correct".
Springfield headspaces all M1A's to shoot commercial ammo as suggested by the factory.All SA M1A's will continue to be headspaced this way and most,if not all other brands of M1A's as well.
You can shoot surplus ammo with these headspace settings but, you should use good surplus ammo when doing so.The neck on some surplus ammo may be longer by as much as .006 and may not chamber.
To prove this point,most guys shoot surplus ammo with headspace set at 1.632 "with no problems".
I shoot a Supermatch SA (1978 receiever) I built myself with a Krieger barrel and McMillan stock and it's headspaced at 1.6315.
I have shot LC military match with no problems at all.In fact,all my M1A's are headspaced under 1.632 and I've never had any problems (or anyone else).
Here's something I didn't add to the earlier thread.
The difference in headspace gauges is in the way each manufacturer gauges a chamber from the case head to the shoulder.This is what I was told by the manufacturers who makes the gauges.Don't worry about the numbers because the important thing you need to know is if the bolt will close on a "GO" "NO GO" or "FIELD" gauge set to commercial standards.These are not military issued rifles.
I won't elaberate on this because it's beyond explaining in a way that I can get you all to understand.
If it was not correct for SA (and everyone else) to headspace M1A's this way they wouldn't be doing it.We are not in the military shooting in dirty conditions that justify military spec. headspacing.
Fly high,shoot low and you'll hit'em everytime.warbird out.
I don't believe the original post mentioned Match M14 or match ".308" ammo. Many folks look long and hard for real M14 barrels which, of course, have M14 chambers (so called 7.62mm chambers) not SAAMI minimum spec chambers.
1.630 - 1.634 may work. It's tighter than the M14 chamber spec, however, and this is a self loading rifle not a bolt action. If you want to shoot match ammunition this may have benefits. If you want a reliable service weapon shooting service ammunition ensure the chamber is not SAAMI minimum specs.
Springfield Inc. probably short headspaces their rifles to avoid legal problems by exceeding SAMMI specs which many folks confuse with safety.
A 1.6300 chamber is unlikely to be reliable with other than specific ammunition. 1.6340 is probably fine.
Well, I thought before I posted,and at the risk of sounding stupid,I will ask this anyway. I am new to this weapon and value the knowledge I glean from this and other sites.I have a S.A. standard that came with a tag stating the headspacing @1.634. I have fired Port. and Sth. Afr. ammo in it with no problems. I also have been reading about "slam fire" in this and the M1 rifles, after reading the previous post, I am a bit concerned about the head spacing in my weapon. I've disconnected the bolt from the operating rod, and gently hand chambered rounds from the mentioned manufactures,they both chamber easily. Is this good enough or should I take her to the local 'smith. Also, what are the dimensional differances between 7.62 and .308? Thank you in advance. Phil
I don't believe the original post mentioned Match M14 or match ".308" ammo. Many folks look long and hard for real M14 barrels which, of course, have M14 chambers (so called 7.62mm chambers) not SAAMI minimum spec chambers.ChuckS
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I made my point by saying that guys (and gals) shoot surplus (mil-spec) ammo in commercial headspaced chambers.I'll also say that my point was well made for which you have no defense.
I also used my match rifle as another fine example of being able to shoot mil-spec ammo in a commercial headspaced chamber.
Since most folks here don't have the experience or expertise in the firearms manufacturing process,things are best kept simple.Everyone is here to learn,share info. and enjoy a hobby that we all have in common.
Howdy pahaska,
The best thing to do is to follow the manufacturers recommendations on the type of ammo to use.If in doubt,call them.SA 1-800-680-6866.I think you'll find that many people shoot Port,Aussie and Hirt in the SA M1A with very good results.
I'll suggest this.Always use ammo in good condition and keep that girl in top shape.We hope to see ya around more in the future.
1.634" headspace is darn near perfect. It's within Warbird's magic range for match rifles and within the specs for the M14 Rifle which shoots 7.62mm NATO.
Slam fire? I've yet to see or see documentation of a M14 or M1 "slamfire" which didn't involve reloaded ammunition. Personal attempts to induce this with service ammunition on these two rifles and the M16 have failed. This is a literal non-problem.
The ammunition you mention, Portugese M963 Ball and South African R1M1 Ball is 7.62mm NATO spec ammunition. It probably was sold and labelled as ".308" ammunition. If pasting .308 labels on boxes of 7.62mm ammo is all that's required to change it there can't be any meaningful differences. The guys at the gun store will shriek that you shouldn't fire 7.62mm ammo in a .308 rifle -- and they sell "converted" .308 ammo by the crate. (And .223 ammo that started life as 5.56mm.)
In our experience with our semi-automatic M1A rifles if the head space is 1.632" or less the rifle will not shoot more than ten rounds as fast as the trigger can be pulled before a spent case fails to extract. We've seen this occur with Portugese, British and South African surplus and PMC commercial ammo. After changing bolts to get a minimum of 1.633" head space we no longer see stuck cases in rapid fire.
The original barrel (a commercial non-chromed standard contour model) on my NFA registered select fire M1A had a head space of 1.6355". It was mated to a TRW bolt. I have replaced the barrel and bolt on this rifle. I installed a chrome plated TRW barrel and a Winchester bolt. The head space is now 1.633". I've shot various makes of surplus ammunition through this TRW barrel in semi-automatic and automatic. With the old commercial barrel and this new TRW barrel I've never had any problems. Every time I pull the trigger this select fire M1A keeps eating cartridges and spitting empty cases. 8) FWIW
Drawing J7267000 calls for a head space of 1.6355 + 0.0030 inches. (U.S. RIFLE M14 from John Garand to the M21, by R. Blake Stevens, page 229).
The measurements that Chuck S say are correct...IF YOU ARE USING 7.62 NATO ONLY...as the M14 was designed to use 7.62 NATO ammo, not .308.
But what we have today are civilian versions of the M14, and people shoot both .308 and 7.62 NATO in these rifles.
If you are using .308, you need to have headspace within .308 SAAMI specs.
If you are going to use only 7.62 NATO you can have the M14 military spec headspace.
So, if your rifle closes on a .308 SAAMI FIELD REJECT gage but does not exceed military specs then you should not use .308 but can use 7.62 NATO.
The main difference between .308 and 7.62 NATO is in the case thickness, not external dimensions, although as warbird says, some lower quality 7.62 is longer...but remember there is 7.62 surplus made by some countries that IS NOT NATO spec...if there is no circle+ on that ammo it should be suspect.
A longer headspace will help reliability with machine guns and those weapons that are used in war time situations that have a higher probablity of having a build up of residue in the chamber area.
The thicker case of the 7.62 NATO round can expand within the larger chamber of the military M14 when the .308 SAAMI spec case may not.
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For the SA made NM rifles for 1964 National Matches the headspace was to be 1.6355-1.6385 inches.
The USAMTU Standards and Procedures for Rebuild of Rifle 7.62 mm M14 National Match to meet USA-MTU Specifications (1968) states that headspacing will be held to the following dimensions: Go=1.633, NO-GO=1.636.
Remember, the above two specs are for 7.62 NATO, not .308, but shows how specs changed for the same ammo, and that in the second example, 1.633 good for both 7.62 NATO and .308.
The above posts were edited for informational purposes. No technical information was either changed or deleted. The Range Officer
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