What's the diff. between 762x51 and .308

.308 headspace measurements start at 1.630" being the GO and 1.634 is no go... In a bolt gun.
7.62x51 starts at 1.6345" being Nato Match, 1.635" being go
And I believe 1.644 is nato no go.

To sum it all up, in most M14s/m305 rifles it is regarded as safe to use 308 in chambers from 1.630 up to 1.640"
And safe for 7.62x51 from 1.6345" to 1.644

So if your rifle is 1.638" , you should be good to for BOTH ammunition
 
Thanks Doc , Copied that info..

well played H wally , I found to the site and have it in my favorites for use later...lol
 
And a big diff is thicker brass for the military round with subsequently reduced powder capacity as compared to the .308.
 
gnmontey said:
http://www.thegunzone.com/m1akb.html:eek:

Could not resist. Mods, please don't ban me:wave:

http://www.303british.com/id36.html:confused:

Been thru this same agony myself. Don't fret it, just don't push the envelope!

Envelope being, MilSpec velocities and bullet weights. Keep in mind, it's a clone of a MilSpec rifle.

M
Click to expand...



OMG what a f**king kB. Eye protection is essential,... essential I'd say.

Possible reasons for this detonation,

- Wrong powder, too fast full charge, chamber pressures through the roof 200,000+.

- Stuck projectile in barrel.

-Oversized bullet loaded in case. .311 bullet in .308 case. If the factory loaded .303British somewhere in the facility and a 150gr PSP .311 found it's way to the bulk box. You would assume they have to pass through an opening to prevent this happening.

-Case underfilled from error or faulty metering powder dispenser, excessive air space with some powders cause detonation rather than progressive burning.


After reading the testimony form the range report, and seeing it was factory ammo, we should be able to rule out all but undercharged round.

But isn't factory rounds weighed for this accidental undercharge to be dropped out of the assembly line? If it was a total powder mix up in a factory lot loading like the .30M! carbine story, thats a disaster in every trigger pull for the whole lot ,wow! All of the above could have happened on the bench, but in an ammo factory?.

Thanks for the post, Monty, reminds me to keep my GD glasses on ,even if at times I get frustrated with old failing vision and cheap polycarbonate optically incorrect glasses shooting those irons.:bangHead:
 
M14Doctor said:
.308 headspace measurements start at 1.630" being the GO and 1.634 is no go... In a bolt gun.
7.62x51 starts at 1.6345" being Nato Match, 1.635" being go
And I believe 1.644 is nato no go.

To sum it all up, in most M14s/m305 rifles it is regarded as safe to use 308 in chambers from 1.630 up to 1.640"
And safe for 7.62x51 from 1.6345" to 1.644

So if your rifle is 1.638" , you should be good to for BOTH ammunition
Click to expand...

So if an overpriced M1A stamped 7.62mm on reciever and 308 on barrel, head spaces 1.632 it is "considered" unsafe to shoot 7.62 X 51 NATO ammo in it?
 
A headspace of 1.632 .... I wouldn't recommend factory nato 7.62x51.
You would be crush chambering the round.
Easiest way to know is to strip the bolt and place the stripped bolt in the rifle , place a round in the chamber and try and close the bolt to full lug engagement. This will tell you if that ammo is "safe"
Nate match is 1.6345", Go is 1.635" so on my bench... NO it is not wise to fire NATO spec ammo in a 1.632 chamber.

These ammunition/chamber dimensions exist for a reason and that reason is safety. It's really not that hard to figure out
 
What? I've shot 7.62X51 in 1.631 and 1.632 M1A's for years with no issues. In the states it is generally accepted that 1.632 is the optimum headspace for using both .308 or nato. The rifle you built for me ate nato without issues (brass was perfect) and she was 1.631
 
I answer these questions with "liability" in mind.
So basically for me I don't want to say yes , sure, go ahead and do that, lot's of guys shoot tight chambers. But as a gun builder, I have to watch my responses because if someone blows up there gun based on a comment I make, it's kinda my ass on the fire.
Remember, I'm just one guy on the internet, with my own opinions on what's safe and not safe. Best thing to do is more research.
If I remember correctly, skullboy built a super tuned m14 with headspace of 1.628. My guess is this rifle would have a couple thou set back after the first few hundred rounds, so headspace probably ended up bang on match .308. I'm only guessing. He would be able to chime in on how that rifle functioned with it's 2 thou crush.

Reloading ammunition and headspace are two topics that, for me, I don't like to say too much and if I do , I have liability in mind so my answers will be along the lines of "what is known to be safe" .... Make sense?
 
gnmontey said:
http://www.thegunzone.com/m1akb.html:eek:

Could not resist. Mods, please don't ban me:wave:

http://www.303british.com/id36.html:confused:

Been thru this same agony myself. Don't fret it, just don't push the envelope!

Envelope being, MilSpec velocities and bullet weights. Keep in mind, it's a clone of a MilSpec rifle.

M
Click to expand...

IT TOOK ME A VERY VERY LONG TIME TO FORGET THAT POOR M14 AND WHAT HAPPENED .. your now responsible for the subsequent nightmares i get to have for the next 3 weeks..
 
M14Doctor said:
I answer these questions with "liability" in mind.
So basically for me I don't want to say yes , sure, go ahead and do that, lot's of guys shoot tight chambers. But as a gun builder, I have to watch my responses because if someone blows up there gun based on a comment I make, it's kinda my ass on the fire.
Remember, I'm just one guy on the internet, with my own opinions on what's safe and not safe. Best thing to do is more research.
If I remember correctly, skullboy built a super tuned m14 with headspace of 1.628. My guess is this rifle would have a couple thou set back after the first few hundred rounds, so headspace probably ended up bang on match .308. I'm only guessing. He would be able to chime in on how that rifle functioned with it's 2 thou crush.

Reloading ammunition and headspace are two topics that, for me, I don't like to say too much and if I do , I have liability in mind so my answers will be along the lines of "what is known to be safe" .... Make sense?
Click to expand...

I understand liability and your reasoning. It's interesting because lots of discussion around 308 and 223 is wether 7.62 and 5.56 is safe to shoot in them. Many people insist that it is and many don't.
 
J996 said:
That KB has been around for a long time. The cause was found to be the barrel, it fatigued and eventually blew.

It's all here. http://www.thegunzone.com/m1akb/762r.html
Click to expand...

Thanks J996. Guess I'm not much good at CSI. Never noticed the normal pressure appearing primer, except for the backing out, I guess as the receiver broke and bolt face did not suppport the base of the cartridge anymore. Safety Glasses forever.
 
Another source

"Before we go much further, we want to address the oft-posed question “Are the .308 Winchester and 7.62×51 NATO one and the same?” The simple answer is no. There are differences in chamber specs and maximum pressures. The SAMMI/CIP maximum pressure for the .308 Win cartridge is 62,000 psi, while the 7.62×51 max is 50,000 psi. Also, the headspace is slightly different. The .308 Win “Go Gauge” is 1.630″ vs. 1.635″ for the 7.62×51. The .308′s “No-Go” dimension is 1.634″ vs. 1.6405″ for a 7.62×51 “No Go” gauge.

That said, it is normally fine to shoot quality 7.62×51 NATO ammo in a gun chambered for the .308 Winchester (though not all NATO ammo is identical). Clint McKee of Fulton Armory notes: “[N]obody makes 7.62mm (NATO) ammo that isn’t to the .308 ‘headspace’ dimension spec. So 7.62mm ammo fits nicely into .308 chambers, as a rule.” You CAN encounter problems going the other way, however.
 
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