compressed loads

jbyrd · August 19, 1999, 04:43 PM

What are the advantages/disadvantages to using compressed powder loads? Does it really matter?

bfoster · August 19, 1999, 09:10 PM

jbyrd... There are at least two distinct advantages to using compressed loads.

First, for both handguns and rifles across the entire spectrum of powder burning rates, if the harmonics developed by shooting a given load are compatable with a particular barrel, accuracy will almost invariably be improved by using a compressed load because the variable of powder position within the cartridge is removed. That said, the degree of improvement varies from small to spectacular. Mick McPherson published an interesting discussion of this phenomenon as it relates to handguns and bullet seating depth a couple years back.

Second, in rifle cartridges, when using medium to heavy for calibre bullets with a slow burning powder there is much less chance for pressure "excursions" or "spikes" to happen in an otherwise modest load. I'd never recommend loading any rifle cartridge with a powder equal to or slower than IMR 4350 to less than 85% density, and would recommend loading powders equal to or slower than IMR 4831 to 90% density. There have been too many well documented "spontaneous disassemblies" over the past 50 years which are attributable to no other cause. Some of the propellant manufacturers recommend this or something very similar. Compressed loads obviously don't suffer from this problem.

I've avoided the physics, but if you are interested repost & I'll try to make that aspect clear enough for a general discussion. Bob

GreybeardB · August 20, 1999, 08:53 PM

jbyrd,
I'm not familar with compressed handgun loads but all my pet rifle loads are compressed. My .270, 22-250, & .223's are charged to the top of the case mouth,then are shaken down almost to bullet seating depth. The bullet then compresses the powder upon seating. I didn't plan this, it just worked out this way on all three calibers.
I try not to push a boat tail bullet into a case full to the mouth with powder. Some powders will "squish" around the bullet causing the case neck to be oversize & may cause pressures to jump up & bite you !
May not be so ironic that performance peaks in my three loads with compressed powder. Look at Hornadys Lite Magnums. Try removing the powder from one of them,then, put it back in again. Now I'm sure they use a process other than compression to get more powder in there than the casing will hold, but it sure mimics a compressed load !

------------------
Ralph in In.

August 19, 1999, 04:43 PM	#1
jbyrd Junior Member Join Date: July 14, 1999 Posts: 9	What are the advantages/disadvantages to using compressed powder loads? Does it really matter?

August 19, 1999, 09:10 PM	#2
bfoster Senior Member Join Date: October 13, 1998 Location: N. of Fords Switch, OK, USA Posts: 297	jbyrd... There are at least two distinct advantages to using compressed loads. First, for both handguns and rifles across the entire spectrum of powder burning rates, if the harmonics developed by shooting a given load are compatable with a particular barrel, accuracy will almost invariably be improved by using a compressed load because the variable of powder position within the cartridge is removed. That said, the degree of improvement varies from small to spectacular. Mick McPherson published an interesting discussion of this phenomenon as it relates to handguns and bullet seating depth a couple years back. Second, in rifle cartridges, when using medium to heavy for calibre bullets with a slow burning powder there is much less chance for pressure "excursions" or "spikes" to happen in an otherwise modest load. I'd never recommend loading any rifle cartridge with a powder equal to or slower than IMR 4350 to less than 85% density, and would recommend loading powders equal to or slower than IMR 4831 to 90% density. There have been too many well documented "spontaneous disassemblies" over the past 50 years which are attributable to no other cause. Some of the propellant manufacturers recommend this or something very similar. Compressed loads obviously don't suffer from this problem. I've avoided the physics, but if you are interested repost & I'll try to make that aspect clear enough for a general discussion. Bob

August 20, 1999, 08:53 PM	#3
GreybeardB Member Join Date: June 23, 1999 Posts: 58	jbyrd, I'm not familar with compressed handgun loads but all my pet rifle loads are compressed. My .270, 22-250, & .223's are charged to the top of the case mouth,then are shaken down almost to bullet seating depth. The bullet then compresses the powder upon seating. I didn't plan this, it just worked out this way on all three calibers. I try not to push a boat tail bullet into a case full to the mouth with powder. Some powders will "squish" around the bullet causing the case neck to be oversize & may cause pressures to jump up & bite you ! May not be so ironic that performance peaks in my three loads with compressed powder. Look at Hornadys Lite Magnums. Try removing the powder from one of them,then, put it back in again. Now I'm sure they use a process other than compression to get more powder in there than the casing will hold, but it sure mimics a compressed load ! ------------------ Ralph in In.