Subject: Re: 22-250 Muzzle Pressure & Volume
From: sfaber@netcom.com (steve faber)
Date: Feb 05 1996
Newsgroups: rec.guns

In article <4etc2v$ma6@xring.cs.umd.edu>,
Scott E. Hall <Sehall@Ptbo.Igs.Net> wrote:

#Does anybody out there have any information or know of an ACCURATE
#place for information on the approx. muzzle pressure and volume of gas
#discharged from a typical 22-250 Rem. cartridge??  Or a cartridge of
#similar volume/caliber as a reference (ie..223, .220 etc.)??  I do
#have accurate breech pressures, but have found no source for muzzle
#pressures.  Any help would be exrteamly appreiciated.

If you have the pressure curve such that you know the breech
pressure at the bullet exit time, then you can estimate
the muzzle pressure by the classical solution   Ps/Pb = 1+C/(2*w)
where C is the powder charge weight and w is the bullet weight.
A more accurate estimate may be to use the isentropic expansion
assumption :
		Ps/Pb = (1+((gamma-1)/2)*(v^2/(gamma*R*T))))^gamma/(gamma-1)

where v is the velocity of the bullet, R is the gas constant/mw of gas, 
and T is around .7*T0  where T0 is the temp of the burning powder gas.
See "Interior Ballistics of Guns" by Krier and Sommerfeld 
The Frankford Arsenal book on  Silencers has some good formulas too.