keith@cs.UMD.EDU (06/14/91)
Hello,
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. I shoot 130 grn bullets, BTW. Would the cup
pressure go up or down? Could it possibly damage a rifle? What about
the sound level? Would it be significantly lower or just a little lower?
I am just wondering about this since a friend and I were talking about
it and we could not come with a good answer. Thanks for any answers.
Keith M. Boyd
---
| Keith M. Boyd (NCR E&M Cola.) | Nothing could be fina' than huntin' and |
| 3325 Platt Springs Rd. _______| fishin' in South Carolina! -Me- |
| West Cola., S.C. 29170 | Std Disclaimers | keith@clodII.columbiasc.NCR.COM |
| ph: 803-791-6419 | From uunet: !uunet!ncrcom!ncrcae!sauron!clodII!keith |gmk@falstaff.mae.cwru.edu (Geoff Kotzar) (06/15/91)
In article <35613@mimsy.umd.edu> uunet!clodii.columbiasc.NCR.COM!keith@cs.UMD.EDU writes:
#Hello,
# 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. I shoot 130 grn bullets, BTW. Would the cup
#pressure go up or down? Could it possibly damage a rifle? What about
#the sound level? Would it be significantly lower or just a little lower?
#I am just wondering about this since a friend and I were talking about
#it and we could not come with a good answer. Thanks for any answers.
#
# Keith M. Boyd
#
#
#
#---
#| Keith M. Boyd (NCR E&M Cola.) | Nothing could be fina' than huntin' and |
#| 3325 Platt Springs Rd. _______| fishin' in South Carolina! -Me- |
#| West Cola., S.C. 29170 | Std Disclaimers | keith@clodII.columbiasc.NCR.COM |
#| ph: 803-791-6419 | From uunet: !uunet!ncrcom!ncrcae!sauron!clodII!keith |
Keith you don't state which powder you are using at present and this is VERY
important. Some powders do not take kindly to reduced loads where loading
density drops below something around 85%; the critical powders are classed
as slow or very slow like 4831 or 7828 from DuPont or 4831, 570, or 870 from
Hodgdon. These are not the only ones; there are several others from all the
powder suppliers. Reduced loads from this class of powders have been known
to produce very dangerous pressure excursions that have wrecked rifles. The
medium burning rate powders like 3031, 4064, 4320 from DuPont, Reloader Nos.
7 and 12 from Hercules and similar powders are better suited to your needs.
I think you need to consult either the Lyman manual or the Speer #11 manual.
I think Speer lists reduced loads using DuPont SR 4759 and you could use
the Lyman data for their cast bullets if you were cautious. Remember that
cast bullets tend to produce lower pressures than jacketed bullets of the
same weight in rifles. The starting loads should all transfer without any
problems though; the maximum loads would be different and you would have
to approach them cautiously. Geoff Kotzarbercov@bevsun.bev.lbl.gov (John Bercovitz) (06/15/91)
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? #What about the sound level? Would it be significantly lower or just a #little lower? I guess that would depend on whether or not she blows up. It would be a lot lower noise level if everything goes well since pressure varies with load according to a fairly high exponent. (The exponent varies too.) JHBercovitz@lbl.gov (John Bercovitz)
petert@uunet.UU.NET (Peter Toth) (06/15/91)
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
gmk@falstaff.mae.cwru.edu (Geoff Kotzar) (06/18/91)
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.
srg@quick.com (Spencer Garrett) (06/19/91)
Others have posted warnings about pressure excursions, but I thought I'd add that there is at least one powder on the market that's very good for reduced loads in rifle cartridges. H4895 (and its clone IMR4895) ignite and burn consistently even with dramatically reduced loads. The Hodgdon manual even claims their powder retains target accuracy down to 3/5 normal loads. I've tried it and it works very well.
rrubert@netman.intel.com (06/22/91)
Regarding the following: From:snitor!petert@uunet.UU.NET (Peter Toth) Message-ID: <35692@mimsy.umd.edu> #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 Does anyone know if the problem goes away with the use of an inert filler to keep the powder in a uniform position and density? Rod Rubert