[geeks] Re: [rescue] Octane R10K/175 CPU module available

[Phil Stracchino]

On Sun, Dec 07, 2003 at 09:47:25PM +0200, Geoffrey S. Mendelson wrote:
> Phil Stracchino wrote:
> 
> > Actually, no ....  I think you have those numbers backwards.  Or their
> > proprtions, anyway.  My recollection is that the .30-06 Accelerator
> > achieves on the order of 5000fps, but it's been twenty years since I
> > read anything about it, so my memory could be in error.
> 
> .220 swift, a .30-06 necked down to .223 does about 5200fps.

My recollection is the .220 Swift is around 4000fps.  But I don't have
any of my loading manuals unpacked, so I can't verify.

All other things being equal, a 55gr .223 projectile in a 5gr plastic
sabot in a .300 bore is going to exit the muzzle going a lot faster than
a 55gr .223 projectile in a .223 bore over the same powder charge, for
two reasons -- powder gases will flow more easily through the wider
bore, and there's almost twice the area for the same gas pressure to act
on.
Back-of-envelope calculations follow:

F = Pa, and also F = MA, so Pa = MA, so with 1.8 times the area and
approximately 1.1 times the mass, we get around 1.65 times the
acceleration, and since v^2 = 2As, we should end up with about 1.29
times the muzzle velocity.  Given that I may be off a few grains on the
weight of the sabot, this is in general good agreement with ~4000fps for
.220 Swift and ~5000fps for .30-06 Accelerator.

To reverse this velocity ratio would require that .220 Swift develop,
hmm....  we need 1.65 times the acceleration with only .55 of the bore
area ... neglecting gas flow, a hair under 3 times the average chamber
pressure of the .30-06, which would put it in the 150,000 CUP range,
which is obviously absurd.  You'd blow the action to pieces on the first
round, and the bolt would probably exit the back of the shooter's head.

(I'm also pretty sure I remember G&A headlines around 1978 screaming
that the Accelerator had finally broken the 5000fps barrier.)


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