It is Tuesday Tar!
Dec 15, 2010 19:40:58 GMT -5
Post by screwbolts on Dec 15, 2010 19:40:58 GMT -5
Instead of using a wild guess on what appears to be "intuitively obvious", go actually look at the reloading data available to you. Pick a cartridge like the 45 ACP and compare the same loads with lead and XTPs of the same weight and the pressures measured. There is not much difference in the pressures actually achieved with the same loads between cast and jacketed "boolits" even though as you indicated the lead engraves much easier. Most are well under 5% with 2% or less on many pressure recordings. The engraving is done in the first tiny fraction of a millisecond considerably before max pressure is ever achieved.
Thank you Chuck for suggesting I go open a reloading manual, I have/had/did. Please take a look at Pages 476 and 477 of the LEE Modern Reloading, it is one of the few that list pressure. this is with 45ACP as you recommend (200 gr J, verses 200Gr LEAD), there seems to be a universally common 5% less Powder used with lead to achieve the same velocity as J word bullets ( sorry they don't specify XTP) and this is done with an average of nearly 6% less pressure.
Now for Lyman 25th edition page 181. Sorry no pressure listed, but for 185 gr side by side. ( Lyman does list the REM 185 as the J projectile and their 452389 as the Cast) There are 6 loads listed for both the J bullet and the Cast, Identical powders listed, in the same order for both. Lyman uses the same gr load for both, ( this be the same powder charge to clarify) They list the achieved Max velocity of the Cast at 12.469 % higher for the six loads averaged together. Being they show no pressure for either projectile I can not assume anything there. It is safe to say that both projectiles were in the safe max pressure, the Lead slid easier and achieved a higher speed is all I can get from this. Nearly 12.5 % faster is a considerable drop in friction in the bore. With Lyman the same 5" 1911 (Colt Government Model)was used for both projectiles so this does enhance the 12.5% increase do to less friction in the very same barrel.
This does not really help Richard in any way with his testing, (I am sorry Richard for muddying the water) the point I probably poorly made or was trying to make is there really is IMO a big difference in a chamber fired load and a loaded from the muzzle load. I can not even factored in the amount of bullet jump, airspace in the cartridge verses projectile setting on the charge, Not to mention the excess fire from a 209 primer verses a Small Pistol standard primer. Just the excess fire from the 209 will change the burn characteristics of a given charge that is lit with a regular rifle primer.
I am sorry that I muddied the water.
Great work Richard, Their is much to learn from your work.
Ken