6000 fps from a .30-378 Weatherby!?


#1

The United States Army’s Redstone Arsenal requested a rifle cartridge that could develop 6,000 ft/s (1,800 m/s) for the effects of light bullets against armor. The .30-378 Weatherby Magnum was able to attain over 5,000 ft/s (1,500 m/s). A while later using a slower burning denser propellant the .30-378 Weatherby Magnum surpassed the US Army’s requirement of 6,000 ft/s (1,800 m/s).

How is 6000 fps possible in the ballistics world? Isnt ~5000 fps the top limit for conventional propellants? If not, what are those bullets made of if they can hold together flying faster than a mile per second? What was the bullet weight too? Even a 40 grain bullet has more energy than a .30-06 at those velocities! Conventional 147 grain M80 ball bullets would almost hit .50 BMG power!


#2

What year was this done?

The bullet likely was made of solid brass, copper, soft iron or thelike.


#3

120mm tank gun APFSDS ammo gets up to 1,740 m/s, and that’s for serious shooting at the enemy, not as a test-bed.


#4

http://en.m.wikipedia.org/wiki/.30-378_Weatherby_Magnum

Wikipedia references in URL link above^

Citing work is always important, especially for everyone else whom may not be familiar with the topic (IMHO)

-Dave


#5

Dave, thanks for the link!

Did any of these initial military test cartridges survive and do exist somewhere?


#6

I sure hope so EOD. I would love one.


#7

The 120mm round operates at up to 85,000psi (which requires steel cases) to get 5000fps. Obviously, a lighter projectile will go faster, but there is still a limit. Conventional wisdom with conventional guns (shoulder arms) is that the gas goes 5000fps, which is why it is impractical to get much over 4000fps with a reasonable barrel length. I’d like more info on how Roy got over 6000fps. I have wondered when some speed demon will make a gun/cartridge working at the higher pressures. It would require special primers and would shoot out the barrel faster. Quickload shows some military calibers (25-35mm) that operate at 75,000 - 80,000psi.


#8

That’s interesting, given the 120mm have combustible cases.


#9

If one was to use a plastic sabot (SLAP round or Rem Accelerator technology) combined with the Gerlich squeezebore principal, and jacked up the pressures, I wonder what speed could be achieved?


#10

The sabot and the squeezebore are basically exterior(!) ballistic tricks to have a small flight diameter (less air drag) for a conventional bore diameter.
In the end the amount of available propellant (grains per grain of projectile mass) is the governing factor. Pressure can be increased, but this is limited by mechanical properties of a conventional rifle/cartridge design. The case capacity of the cartridge basically defines the upper limit.
A plastic sabot will probably not do, because even a conventional jackted bullet like M80 starts to suffer deformation at launch speeds of about 3200 fps.


#11

I understand the Abrams round uses a steel base to seal it, though the case walls were combustible. That was the original M829, I don’t know if the steel has been eliminated in newer versions. There are caseless mechanisms and I believe the attempts at consuming cases are similar, since the materials are not as strong as brass or steel, but they haven’t become widespread. Brass flows at pressures above about 65,000 psi.