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From: gmk@falstaff.mae.cwru.edu (Geoff Kotzar)
Newsgroups: rec.guns
Subject: Re: Downloading Centerfire rounds
Message-ID: <35750@mimsy.umd.edu>
Date: 17 Jun 91 21:30:50 GMT
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Organization: Case Western Reserve University
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In article <35692@mimsy.umd.edu> snitor!petert@uunet.UU.NET (Peter Toth) writes:
#In article <35665@mimsy.umd.edu> bercov@bevsun.bev.lbl.gov (John Bercovitz) writes:
##In article <35613@mimsy.umd.edu>
## uunet!clodii.columbiasc.NCR.COM!keith@cs.UMD.EDU writes:
##
###   I am curious about what would happen if I were to download a .270cal
###round from my normal 50 grns. to say...about 30 grns. Would this be a
###dangerous thing to do?
##
##You could probably get away with it for years, but enough people have
##blown up their rifles this way that it's not worth taking the chance.
##The theory of why these low-loading-density detonations happen is not
##well developed.  I think the best explanation is to be found in 
##"Pressure Factors" by Brownell, Wolfe Publishing.  c1990?
##[...]
#
#How about: you are more likely to see this problem with "fast" powder.
#
#The problem with the half empty case is that you get flame propagation
#end to end faster than you can say "Oh #@%*!" ;^)  If it's a slow powder,
#no matter, or not much; if it's a fast one, don't do it next to me =%0.
#
#petert

John Bercovitz is right about which burning rate powders are susceptible
to low loading density explosions: it is the slow or extra-slow powders.
For a long time people did not believe that smokeless powders could
detonate and attributed the wrecked rifles to reloads that had been loaded
with the wrong powder. When they finally accepted that it was happening
to too many conscientious reloader using Hodgdon's 4831 to be poor reloading
technique all sorts of explanations were heard. One was that the violence
of the primer going off would ignite and shatter the grains of powder since
they were not completely constrained. This resulted in a "moderate" load of 4831
being converted into an excessive load of something like 4227. The really big
problem was that it could not be reproduced on demand in the ballistic labs
so nobody could even begin to test out the hypotheses. Within the last two
or three years there was an article in Handloader Magazine by a fellow who
was able to produce these pressure excursions - also named at one time SEE
for secondary excursion explosions I believe -  on demand in his rifle. One
point that comes out in the "Pressure Factor" articles is that the excursions
are occurring with these slow powders with great regularity but it requires
a piezoelectric pressure transducer and an oscilloscope to monitor them. The
old crusher system for measureing pressures missed the lower amplitude but
more common ones entirely. It isn't a question of are the pressure excursions
occurring with the reduced loads of slow burning powders but rather how
extreme are the amplitude fluctations. People were only paying attention
when rifles were destroyed.