.308 chamber in a M305

IMHO,
applying logic to any thread about headspacing an M14 rifle is a waste of time ...
but I will try applying logic anyhow.
Logically
IF
the Norinco bolt is properly heat treated ... and most of them are
AND
IF the norinco bolt is properly fitted for complete and even bearing on BOTH lugs ... and some of them are ... or they can be quickly lapped in
THEN the Norc bolts can be ALMOST as good as GI, and probably much better than any of the CAST bolts available with many new Springfields.
HOWEVER, MOST Chinese bolts have firing pin holes that are larger than GI spec, which makes them susceptible to accumulating crud in the sloppy hole [ especially brass shavings ] potentially blocking the firing pin travel ... and this would NOT be a good thing.
PLUS, MOST of the Chinese bolts have firing pins which are ground a little too much at the bearing/camming surface at the rear, which can increase firing pin timing lag.

EITHER of these bolt conditions can potentially be MUCH more dangerous in an M14 than MASSIVE headspace.

THEREFOR,
EITHER be daring, and shoot your M14 with the original bolt,
BUT, check that Chinese bolt's firing pin hole for blockages regularly,
OR, be conservative,
and install an expensive, properly lapped in US GI bolt, or at a minimum, a US GI firing pin in good condition.

Either way stop worrying about "HEADSPACE"!!!!!!

Sheeesh ... Halloween is just around the corner, and too many people seem to think that ol' debil' headspace is hiding under the bed, ready to leap out and blow their faces off.

It just don't happen.
BAH HUMBUG
[;{(
LAZ 1
 
With the legions of loyal Norinco fans around,this does tend to get into the realm of emotion more than logic. But,given that you are dealing with a 50,000PSI pressure bloom a few inches in front of your face,it does pay to be temper the emotions with a bit of logic.

With supplies of MILSPEC ball ammo drying up,most folks will want to fire commercial .308 Win in their rifles-especially if the durned things are stamped .308 Win!!. Commercial brass is considerably lighter and less durable than MILSPEC brass(e.g. DA MILSPEC brass avg case weight is 187gr,WRA commercial is 165gr.federal is 175gr). From a gunsmith's liability/CYA point of view, I would not advocate firing commercial .308 ammo in a chamber that exceeds the SAAMI field reject limit of 1.638-even assuming that the preceeding sound comments on bolt condition are satisfied. Having said that,chances are that the worst thing that might happen is a case separation due to brass stretch/twist in an excessively long chamber. My personal decision is to never fire a rifle where the headspace exceeds the "field" limit,but each to his own.

It is always good to establish what the headspace actually is and the reliable way to do this is with a set of headspace gauges. A .308 Win chamber must accept the "go" gauge which measures 1.630. Newly made rifles should not accept the "no-go" gauge which measures 1.634. A rifle is still within spec and is safe to fire if it does not close on the "field" gauge which measures 1.638. I think the ideal/safe dimension for the .308 Win in a gas gun is 1.632. The reason for this is to make some allowance for accumulated firing crud in the chamber and still ensure that the bolt will close freely from the pressure of the op rod spring.

In addition to the .308 Win,folks will also want to fire 7.62mm ammo in these rifles. The dimensions of these 2 cartridges(and the chamber specs)are different,even though many consider them interchangable. The minimum dimension of a 7.62 chamber is 1.6355 (that's 5.5 thou greater than the .308 Win "go" dimension and 1.5 thou greater than the .308 Win "no-go" limit,but it is still 2.5 thou under the .308 Win "field" limit. The dimensions of loaded cartridges do vary,but the consensus is that 7.62 ammo is generally 2 thou longer than .308 Win ammo. Now here's the real eye opener;the 7.62 "field" or reject limit is 1.6455 or 7.5 thou more than the .308 Win "field" limit.

After all of the above I would be comfortable firing heavier cased,and nominally longer, 7.62 MILSPEC ammo in a 308 Win chamber-provided that headspace was at least 1.634 (you will see approx 1 thou set back of the case shoulder as a result of "drive-in" from chambering) and obviously no greater than the 7.62 "field" limit of 1.6455. You can verify free chambering before firing by stripping the bolt and closing the bolt on each cartridge by hand with the op rod removed. Firing long ammo in a too tight chamber is an invitation to trouble with an out of battery detonation because a gas gun relies on the op rod spring pressure alone to close the bolt with none of the camming power of a bolt gun. If one wishes to reload, then tighter headspace is always better in the interests of minimizing case stretching and prolonging case life(5 firing cycles is a safe/practical limit on 7.62 brass).

I have 3 7.62 rifles,a HRA M14 and 2 Garands which I built using the .5 inch shorter Italian 7.62 barrels. For these I stick to MILSPEC brass and ensure a minimum chamber limit of 1.634 (using .308 Win "no-go" gauge). I like the 1.634 minimum because I still have a stash or MILSPEC IVI/DA/RG/M118 Match ammo. My actual chamber length on these rifles is 1.636( established by selective bolt fit on the Garands and sh**house luck with my existing bolt in the M14),which gives me the assurance that I can use commercial .308 cases in them if I want,while minimizing case stretch in the MILSPEC brass which I use for reloading.

As mentioned in my initial post,I'm almost convinced to take the plunge with one of the new .308 Polytech rifles based on the info which is out on them. I'm going to pay very close attention to the headspace before firing it and I've decided to swap in my HRA bolt as a precaution. Most of us cannot get a Rockwell hardness test done,and pretty much all USGI M14 bolts were magnafluxed in service with an "M" etched on the bottom of the bolt to indicate this.
 
I still have a few more battle packs of SA 7.62 which I'll finish off before doing any of this, but it sounds like getting a kreiger barrel sounds like the route I will be taking. For $500 + gunsmithing, I can get a match .308 headspace AND a fancy barrel...

After that, it's all reloaded/commercial .308 for me. Which is the reason why I'm asking on the board, what's the best approach for getting a properly headspaced chamber, and I got the answer!

Thanks guys!
 
purple said:
With the legions of loyal Norinco fans around,this does tend to get into the realm of emotion more than logic. But,given that you are dealing with a 50,000PSI pressure bloom a few inches in front of your face,it does pay to be temper the emotions with a bit of logic.

With supplies of MILSPEC ball ammo drying up,most folks will want to fire commercial .308 Win in their rifles-especially if the durned things are stamped .308 Win!!. Commercial brass is considerably lighter and less durable than MILSPEC brass(e.g. DA MILSPEC brass avg case weight is 187gr,WRA commercial is 165gr.federal is 175gr). From a gunsmith's liability/CYA point of view, I would not advocate firing commercial .308 ammo in a chamber that exceeds the SAAMI field reject limit of 1.638-even assuming that the preceeding sound comments on bolt condition are satisfied. Having said that,chances are that the worst thing that might happen is a case separation due to brass stretch/twist in an excessively long chamber. My personal decision is to never fire a rifle where the headspace exceeds the "field" limit,but each to his own.

It is always good to establish what the headspace actually is and the reliable way to do this is with a set of headspace gauges. A .308 Win chamber must accept the "go" gauge which measures 1.630. Newly made rifles should not accept the "no-go" gauge which measures 1.634. A rifle is still within spec and is safe to fire if it does not close on the "field" gauge which measures 1.638. I think the ideal/safe dimension for the .308 Win in a gas gun is 1.632. The reason for this is to make some allowance for accumulated firing crud in the chamber and still ensure that the bolt will close freely from the pressure of the op rod spring.

In addition to the .308 Win,folks will also want to fire 7.62mm ammo in these rifles. The dimensions of these 2 cartridges(and the chamber specs)are different,even though many consider them interchangable. The minimum dimension of a 7.62 chamber is 1.6355 (that's 5.5 thou greater than the .308 Win "go" dimension and 1.5 thou greater than the .308 Win "no-go" limit,but it is still 2.5 thou under the .308 Win "field" limit. The dimensions of loaded cartridges do vary,but the consensus is that 7.62 ammo is generally 2 thou longer than .308 Win ammo. Now here's the real eye opener;the 7.62 "field" or reject limit is 1.6455 or 7.5 thou more than the .308 Win "field" limit.

After all of the above I would be comfortable firing heavier cased,and nominally longer, 7.62 MILSPEC ammo in a 308 Win chamber-provided that headspace was at least 1.634 (you will see approx 1 thou set back of the case shoulder as a result of "drive-in" from chambering) and obviously no greater than the 7.62 "field" limit of 1.6455. You can verify free chambering before firing by stripping the bolt and closing the bolt on each cartridge by hand with the op rod removed. Firing long ammo in a too tight chamber is an invitation to trouble with an out of battery detonation because a gas gun relies on the op rod spring pressure alone to close the bolt with none of the camming power of a bolt gun. If one wishes to reload, then tighter headspace is always better in the interests of minimizing case stretching and prolonging case life(5 firing cycles is a safe/practical limit on 7.62 brass).

I have 3 7.62 rifles,a HRA M14 and 2 Garands which I built using the .5 inch shorter Italian 7.62 barrels. For these I stick to MILSPEC brass and ensure a minimum chamber limit of 1.634 (using .308 Win "no-go" gauge). I like the 1.634 minimum because I still have a stash or MILSPEC IVI/DA/RG/M118 Match ammo. My actual chamber length on these rifles is 1.636( established by selective bolt fit on the Garands and sh**house luck with my existing bolt in the M14),which gives me the assurance that I can use commercial .308 cases in them if I want,while minimizing case stretch in the MILSPEC brass which I use for reloading.

As mentioned in my initial post,I'm almost convinced to take the plunge with one of the new .308 Polytech rifles based on the info which is out on them. I'm going to pay very close attention to the headspace before firing it and I've decided to swap in my HRA bolt as a precaution. Most of us cannot get a Rockwell hardness test done,and pretty much all USGI M14 bolts were magnafluxed in service with an "M" etched on the bottom of the bolt to indicate this.
Click to expand...

this is the most outstanding post i have seen yet on the topic of m14 headspace, good on ya purple ;)
 
HTH. Shooters are like pilots in some ways. There are old ones and there are bold ones,but there are'nt many old and bold ones. I like to stay on the side of caution-and keep getting older. LOL.
 
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