October 14, 2008
Petzal: The Great Overbore Conundrum
By David E. Petzal and Phil Bourjaily
Once upon a time, the worst thing you could say to a rifleman was that
his cartridge of choice was overbore. Today this would be the equivalent
of calling him a Clintonista, or slapping him. Overbore meant that his
7mm Thunderf***er Magnum burned more powder than it could efficiently
use, and was therefore less worthy in the great pantheon of cartridges
than, say, a 7x57, or a .280, or for all I know, a 7x64. It also, by
extension, meant that the person who shot a 7mm Thunderf***er magnum was
unworthy to enter the Kingdom of Heaven, or was just a squirrelheaded
son of a bitch.
There were other concerns. Huge cartridges that used gobs of powder
burned out their barrels quicker, cost more to shoot, and were more
difficult to shoot than non-overbore rounds. This is all quite true. But
there's another side. Sometimes, you want a bullet to go much faster
than a standard cartridge can manage, and the only way you can do it is
by burning lots and lots of powder. It's the same in automobiles; if you
want more speed, you need proportionately huge increases in horsepower.
An example: My favorite .338 load right now is a 225-grain Barnes XXX
backed by 72 grains of RelodeR 19*. This gives me 2,750 fps, which is
enough for any shot inside 300 yards. If I anticipate a longer shot than
that, I can go to a .338 Remington Ultra Mag, which will gulp down 93
grains of RelodeR 22*, which drives the same bullet at 3,020, making
hitting at long range somewhat easier. It is, as even the dullest among
you can see, a whopping increase in powder for a comparatively small
increase in velocity. But there you are.
Overbore, who cares? They are very useful cartridges under some
conditions, and even now, as you read this, people are making RelodeR
powder and new barrels whether we want them to or not.
*These loads are safe in my guns, but they may blow you into the next
world. That is your concern. I assume no liability from now until the
end of recorded time.