Barrels: more on freeboring .308/7.62x51

thorlin · September 22, 2000, 10:17

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)

<<>>
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.
<<>>

ByronF · September 22, 2000, 11:03

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 · September 22, 2000, 11:38

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 · December 26, 2001, 19:40

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.

September 22, 2000, 10:17	#1
thorlin Registered FALaholic #: 1066 Join Date: Sep 2000 Location: Peoria, AZ - USA Posts: 23	More on freeboring, .308/7.62x51 - Was Freeboring... 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) <<>> 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. <<>> __________________ Mike

December 26, 2001, 19:40	#4
rwwje Registered Contributor FALaholic #: 2017 Join Date: Jan 2001 Location: Texas Posts: 1,417	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. __________________ Conservatives believe that the people are sovereign, and that the government is subject to the will of the people. Liberals believe that the government is sovereign, and that the people are subject to the will of the government.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

September 22, 2000, 11:03	#2
ByronF Registered FALaholic #: 630 Join Date: Aug 2000 Location: PA Posts: 3,174	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

September 22, 2000, 11:38	#3
richg68 Registered FALaholic #: 94 Join Date: Jul 2000 Location: DE Posts: 5	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.