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So I'm planning to buy an SA M1A Loaded, and the dealer has 2 identical models in stock. One with a 1.631 headspace and one with a 1.632 headspace.

I know those are extremely close and are both within spec, but which headspace is technically better? Isn't a smaller headspace better?

Thanks,

J
 

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I don't think those are going to matter. Those are well with in the lower limits. If I had my choice I would take the 1.631 only because if any lapping or changing of bolts needed to be done, it would make it more suitable.

The 1.632" will give you probably the same accuracy as the other one. It will probably have less potential for feeding and extracting problems as well. The bigger the chamber the better it can handle dirt, debris, and fouling.


I did have a barrel on my rifle that headspaced well into the NATO specs and it was a very accurate shooter. Were talking approx. 1.640" or better. It was just hard on the brass and I couldn't get a lot of reloads out of them.



On those two guns I would choose the one that has the best fit and function, best trigger, tighter rear sight, best lock up and best front end tension, instead of what their headspace is. Spend 10 minutes inspecting them to see which is the better built rifle.


Maybe someone on the board that know m14s real well, can go with you if they're in the area???
 

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So I'm planning to buy an SA M1A Loaded, and the dealer has 2 identical models in stock. One with a 1.631 headspace and one with a 1.632 headspace.

I know those are extremely close and are both within spec, but which headspace is technically better? Isn't a smaller headspace better?

Thanks,

J
Check to see if either has any USGI parts, if possible do a tilt test, check to see if the barrel is indexed correctly, chrome lined barrel, headspace is a debated issue on this forum, the 308 headspace is 1.630-1.634, headspace for 7.62x51 nato is 1.6335-1.640.
The best answer is, either is good with the headspace indicated, other considerations are more important given the stated headspace.
My choice would be for as many USGI parts as possible, correct fitting of parts with function tests, check the bolt lug engagement surface.
If you pick one up you need to post some pics.
Have fun, pop some caps and let us know how it went.

Jim
 

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That small difference will make no difference at all, we always chambered the state guns at 1.632". Sam
Sam. Welcome Aboard! Glad to see you here.

Sam is talking about the NM M14's loaned to the Virginia State Association Rifle Team by the DCM. Sam did an awful lot of work for them over the years and he is to be highly praised for his support of The Old Dominion's (Virginia's) State Team.

When I went through the Marine Corps OJT (Apprenticeship) program to learn to be an RTE Repairman (NM Armorer) in 1973-4, it had only been a few years since we had changed over from the NM M1 Garand to the NM M14 as our NM Service Rifle. We believed then that it was best to try to chamber a rifle as closely as possible to where the bolt would JUST Barely Close on .308 GO Headspace gage with no more resistance or friction felt than without the GO Headspace Gage in the chamber. This meant you WOULD feel friction on specially made "NM" 1.631 or 1.632 headspace gages. We were using Lake City NM 7.62mm NM Ammo, the Proprietary Federal NM Ammo that became "Gold Medal Match" in the 90's and a hand load we developed for the "Critchfield Match" which was a combination of 600 and 1,000 yard line scores in those days.

Well in the late 70's or very early 80's, we came to learn that was just a bit too tight for SOME NM M14 rifles, because as the carbon built up in the chamber during firing over the NM course - it caused a very tiny accuracy loss by the time they got to the 600 yard line. It wasn't all or even a majority of rifles, but it was enough that we changed the Headspace check to where the rifle HAD to accept the special NM 1.631 gage with the bolt closing on it with no more resistance/friction than without the gage. This meant you would feel friction on a NM 1.632 or 1.633 Gage.

Now folks, it is NOT easy to chamber a NM barrel that way even when you have a good/sharp reamer and you are being VERY CAREFUL. You sometimes hit hard spots in the chamber metal and you wind up cutting a bit more than you wanted just so you will have a smooth chamber. There were a very few rifles that would accept a 1.633 Headspace gage without resistance/friction and we found they still shot with the same accuracy as with the 1.631 or 1.632 NM Headspace gages.

So is there ANY practical accuracy difference between a 1.631 and 1.632 chamber in the rifles JHN mentioned? Absolutely not!!! FURTHER, there are going to be more differences in how an individual barrel shoots or any single or combination of other factors involved that this difference is meaningless. Even when you are using QUALITY NM headspace gages from the same manufacturer, there will be enough difference in the gages where you MAY feel some resistance on a 1.631 Gage and not on another 1.631 gage - again, from the exact same manufacturer. What we did on THE Marine Corps Rifle Team was order 5 or 6 NM 1.631 Headspace Gages and took the three that best matched each other and issued them to the Big Team Armorers so all our inspections of the chambers would read as identical as possible.

Even if you took TE readings from the two rifles and one was slightly better than the other, that may also not tell you anyting ahead of time. The only way you could really tell which rifle MIGHT be a tiny bit or more better than the other one is to put it in a super expensive test rack or have an extremely experienced shooter shoot both rifles. Even THEN, the rifle that did not perform as well as the other for him MAY perform better for you. OR, the rifle that did not perform as good as the other with one type of ammo, will outshoot the other rifle with a different type of ammo.
 
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