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From: bercov@bevsun.bev.lbl.gov (John Bercovitz)
Newsgroups: rec.guns
Subject: Re: 30-30 trapper
Message-ID: <34836@mimsy.umd.edu>
Date: 24 May 91 04:18:55 GMT
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Organization: Lawrence Berkeley Laboratory, Berkeley, California
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In article <34820@mimsy.umd.edu> lulue@trout.nosc.mil (D Lulue ) writes:
#Is the Winchester Trapper model, with it's 16" barrel, too small a
#gun for the 30-30 round?  I'm specifically thinking about unburned
#powder and muzzle flash.

The short answer is "no".  But allow me to expand a little on the
point.  One way of looking at it would be to note that the 30-30
is often fired in the T/C which has an even shorter barrel than the
Trapper.  There is a bit of incompletely burned powder, but then 
there is a bit of incompletely burned powder when you load 2400
in a 44 Mag. There is also quite a bit of flash visible if you're 
shooting at dusk.  So I guess we need a standard to compare the
potentially too-short barrel against.

I think a good way of looking at it is to compare this firearm's
expansion ratio with that of another, known, firearm.  First a  
definition: the expansion ratio is the sum of the volumes of the 
chamber and the bore divided by the volume of the chamber.  It is 
akin to the compression ratio in your car.  

A 30-30 case will hold roughly 36 grains of water.  The 16" 30-30 
barrel allows around 14.5" of bullet travel and would therefore hold
around 266 grains of water.  So the expansion ratio of the Trapper
will be: (36 + 266) / 36 = 8.4  If a 30-'06 had an expansion ratio
this large, what length of barrel would it have?  The 30-'06's
case capacity is around 61 grains of water.  So: 61*8.4-61= 451gn
of water bore capacity which is the capacity of a 30 cal bore which
has a bullet travel of 24.6".  Add to that the distance from bullet
base to breech face of approximately 2.1" for the '06 and you end
up with 26.7".  So a Trapper with its 16" barrel is equivalent
in this way to a 30-'06 with a 26.7" barrel.  And that's just not
too short.

I've ignored one effect which also helps out:  The 30-30 has the same
bore and the same bullet weight as an '06, but it has a smaller case
capacity so it also uses a quicker powder.  This also helps a little
with the unburned powder and the muzzle flash. 

JHBercovitz@lbl.gov    (John Bercovitz)