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Discussion Starter · #1 ·
Evey M1A owner should know the head space in his rifle.. Head space is a term everyone that owns and shoots a M1A should understand.. This subject has been covered before, maybe before some of the growing number of Members signed on, so a reminder is not out of order..

Listening to a couple of M1A and M1 owners discussing head space recently it was disturbing to hear they both used a Field Test Bolt to determine the head space.. The Field test bolt is not the proper gauge to check head space, that is a mistake to do that. Do not accept a head space reading taken with a Field Test Bolt..

The Field Test Bolts [ for both the M1 and M14] were surfaced ground to known dimensions,, not for the primary purpose of realizing a heads space figure, the primary purpose is to determine if an open head space problem is/was related to receiver breech alignment. In simple terms, that means,, does the receiver line up properly with the breech and chamber... The Field Test Bolt can be used with a head space gauge to make the determination, it usually is used, but not always..

The chamber head space should always be taken with the "BOLT to be Used"... Bolts are different ,,, even M14 bolts, especially the TRW bolts found on today's market. M1 bolts are more different still.. .. Art
 

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'Knowing' the rifle's chamber headspace number is interesting, but the IMPORTANT thing is to make sure that the ammo is a suitable fit into the chamber.

Even if you DO know the rifle chamber headspace number, what good is it?
I've never seen commercial or military ammo marked with the cartridge HS.
For reloading / resizing, you could use gages to adjust the amount of full-length resizing, but the final test is whether your ammo fits your rifle.

1) With bolt open, place a cartridge in the chamber. It should go fully into the chamber with at most light finger pressure.
2) Ease the bolt forward until it stops due to the extractor hitting the base of the rim.
Then use moderate thumb pressure on the oprod to verify that the bolt will fully rotate and lock into the closed position.
3) Open the bolt with moderate pull on the oprod to verify that the cartridge is not jammed into the chamber by the bolt.

If #1 needs a lot of pressure to seat a cartridge in the chamber, then the body of the cartridge is too fat, and is not suitable for the rifle. Or might need smallbase resize die.
If #2 requires a lot of pressure on the oprod to close the bolt (or if the bolt doesn't fully rotate closed), then the headspace of the cartridge is too long for the chamber.
If #3 needs a heavy pull on the oprod to open the bolt, then the headspace of the cartridge is too long and is causing the case to be compressed in the chamber by the bolt.

The M1, M14/M1A rifles are designed for use with ammo that is an 'easy fit' in the chamber - if the case is a tight or jammed fit in the chamber then various problems will happen.

Also, a 'FIELD REJECT' headspace gage is used to check whether chamber headspace is 'too much' for safe use.
A headspace 'GO' gage is used to verify that chamber headspace is not 'too little' for use.
The 'NO-GO' gage is for verifying that on a new rifle, the chamber headspace is not 'too much more' (the mfg spec) than being 'too little'.

Jay Kosta
Endwell NY USA
 

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One issue I've experienced when checking rifle headspace is inconsistency in the precision of the various available commercial headspace gages.

One of my SAI M1A rifles, for example, arrived with a hang tag indicating a headspace of 1.6315". Its stripped bolt will not close when tested using one (respected) manufacturer's commercial .308 Win 1.634" "no go" gage. However, that same bolt does close on a different (respected) manufacturer's commercial .308 WIN 1.634" "no go" gage. At least one of the gages (and perhaps both) is out-of-spec.

The lack of precision of the commonly available headspace gages is troubling. I know it's relatively easy to have the gages checked and "certified," but that process costs more money than many of us are willing to spend.
 

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Art, do the M14 field test bolts have a good enough use to justify getting one for civilian use, or are they strictly a "field" gauge? I have come close to getting one a few times, but I was not sure if it would ever be used. Sure, it would be great and cool to have all these gauges, but right now I am concentrating on the items that I have a use for. As always, thanks for your info and teaching us how-to and why-to.
 

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Discussion Starter · #6 ·
The Field Test Bolts are interesting gauges, With today's commercial receivers and barrels there may be a rare instance of serious misalignment..

One of out Forum members recently purchased a new commercial receiver that was so far out of alignment the bolt contacted the left entrance of the breech,, this could be seen, no Test Bolt was needed..

Except as a Collectable, there is no practical reason to own one in my opinion.. Art
 

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The Field Test Bolts are interesting gauges, With today's commercial receivers and barrels there may be a rare instance of serious misalignment..

One of out Forum members recently purchased a new commercial receiver that was so far out of alignment the bolt contacted the left entrance of the breech,, this could be seen, no Test Bolt was needed..

Except as a Collectable, there is no practical reason to own one in my opinion.. Art
Why not to use as a serviceable bolt? Just as any other bolt. Build a rifle with it, headspace normally and leave it in.
 

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Discussion Starter · #9 ·
Using a Field Test Bolt in a rifle may...

work fine.. Years ago, I can't be certain about this because it has been a loooog time, I recall seeing a shooter with a FTB in a Match M1 Garand..

All the FTB's I have seen and owned had grinding on the face, I assume this was to bring it to some desired measurement. If that measurement left enough material to be safe to use,,, I see no reason not to use a FTB.. The problem for me would be not knowing how much was ground off, the face, I suppose it can be measured if the tools are available. You certainly would have to check the firing pin protrusion.. Did Field test Bolts start life as regular Bolts, does anybody know for certain?

If a FTB is to be used, I suggest mounting the rifle and firing ten to twenty rounds with a looooong string first, check all the items for danger signs..

Good question, nice to hear from you.... Art
 

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Seem that I have read that SA converted some standard bolts to FTbolts. I would guess that the standard bolts would have been specially picked so as to be as close to the desired measurements they desired leaving only minimum truing and grinding, but this is only a guess. I look forward to hearing more from more knowledgeable people on these bolts/gauges. Much to learn....
 

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"The Field Test Bolts [for both the M1 and M14] ... the primary purpose is to determine if an open head space problem is/was related to receiver breech alignment."

Art Luppino, I disagree with your statement above. The field test bolt is use to determine in the case of excess headspace whether the bolt is unserviceable or if the rifle is unserviceable (worn or out of dimensional tolerance bolt locking lugs in case of the bolt, worn receiver locking recesses or too long of a chamber in case of the rifle). It has nothing to do with "receiver breech alignment". See TM 9-1005-223-34, dated 2 August 1972, Chapter 7, Section II, paragraph 7-7j(4).
 
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I believe the ones I have are chromed on the face and then ground. One of mine is chromed on the rear of the lugs. I was hoping you (Art) would know about the hardness issue. I know they are hard because I file won't cut it. I just don't know what procedure was done. If they removed metal from the face then hardened and added chrome I think it would be better than anything out there. However if they hardened them first then ground off some material before chroming the idea starts to get a little sketchy. Chrome is very hard, but it is brittle. I have several of them. I bought them more out of curiosity than anything else. I guess I wanted to hold it myself and inspect it with my own eyes.
 
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