Barrels: more on freeboring .308/7.62x51

[thorlin]

So, extending the freeboring topic...

If freeboring allows "safer pressures", is that to say the it is safer at higher pressures?? Sort of a built in pressure relief?

I ask because I read (on this board, I believe) that .308 Win is NOT 7.62x51, that in fact the NATO round can exhibit higher pressures than the .308 round.

I always see ref's to FALs being ".308" or "7.62x51(.308 Win)". What is reality? Is it .308 or is it 7.62x51 NATO? Does it truly matter? Am I beating a dead horse? Should I stop asking stupid questions??

Thanks,

Mike (still in need of a cool signiture)


<<<SNIP from Brad/GunThings>>>
The rumor is that the freebored barrels were clamped too tightly when removing them from receivers and they were freebored to allow the proper clearance for the projectile. Long ago Weatherby rifles had very slightly more freebore in their barrels due to the high pressures of their cartridges. Generally, freeboring allows for safer pressures, more acceptable use of numerous projectile lengths, and is less accurate. The average deer rifle sold by the big manufacturers will have more freebore than a custom target rifle. Generally, the closer the bullet is to the lands when round is chambered, the more accurate, but pressure may also increase. Manufacturers must compromise since the end user may use 110 gr or 220 grain projectiles.
<<<SNIP>>>

[ByronF]

The freebore's lowered pressure is a secondary effect of it's original purpose: to increase velocity (in the case of Fed Arms kit, to ream out the pinched part of the bore). The barrel encounters no resistance for the lenght of the freebore, so pressure is reduced. Also, powder burn rate is affected by the pressure under which it burns. Note that freebore for velocity purposes is usually not very long. I'm guessing on the order of .125-.250 inch. These FAL barrels were freebored about 1.0-1.5 inches. That's a lot.

I'd advise against getting too creative with reloads on account of this freebore business. This is a gas gun, after all.

And I think you may be backwards on the 7.62 NATO/308 Winchester pressure issue. Me thinks maybe the commercial 308 is the hotter of the two. I almost hate to say this as it may start that whole issue again.


Byron

[richg68]

Yes .308 Win is a hotter load than the NATO round. Same dimensions, just more power. Not sure as to pressure and velocity differences. If you fire the 2, you will notice a much larger flash from the .308 compared to the milt ball stuff.

[rwwje]

richg68:
The amount of flash has nothing (certainly, next to nothing) to do with pressure. Military ammo is commonly loaded with powders containing flash suppression additives. :)