There's an awful lot of "as reported on the internet" and hand-drawn pictures out there.
And an absolutely incredible amount of "...it's well-known..." knowledge.
But does anyone have real data comparing BP v Smokeless pressure curves in BPCR cartridges?
Driftwood Johnson's Post in [Brand-X] three years ago and TexMac http://www.texas-mac.com/Black_Powde...bturation.html begin to address. Taken together the two articles begin to tackle the screaming & yelling matches that go on about what's best for bullet obturation to seal the barrel for cast loads.
I maintain that a fast smokeless powder is far more effective in "upsetting" the cast lead projectile in that regard, when compared to BP. Others take almost a religious zeal in claiming that it's "well known" [aka settled science] that BP gives the fastest "bang" as an explosive. (and then they cite burning powder trails of BP vs smokeless on one's open-air driveway as to the "burn speed" advantages of BP -- which is of course irrelevant.)
While directly applicable to relative risetimes, the texas-mac article limits the discussion to SR4759 -- which was deliberately developed to have pressure risetimes akin to BP. Others state that while smokeless does rise precipitously, "black powder beats it out at the start."
I think Driftwood's presentation puts that in perspective. The key is "equal outcome" -- projectile velocity when exiting the barrel.
https://www.thehighroad.org/index.ph...#post-10703480
(A well-worn image, but one directly applicable to the kind of ballistics of many heavy BCPR cartridges w/ cast bullets)
Since that velocity is a function of work done on the bullet, and that total work is a function of area under the pressure-time curve, the lower/slower BP curve produces the same velocity and rolls over onto peak, and off of peak, at far lower peak than smokeless -- FAR lower.
Meanwhile, the smokeless literally races past that BP peak, in about the same timeframe, to more than twice the pressure. A really sharp "punch" as opposed to a shove. (others will note the short/initial BP rise ahead of the smokeless very early in the game. But that poops out at very low pressures -- far lower than required to begin bullet/material deformation of even the softest alloys)
This is where I would submit that effective bullet upset/obturation occurs -- that sharp high-pressure punch well above Brinell-derived deformation pressure of the alloy (BN*1,420psi) -- and gives significant advantage to smokeless for cast bullet shooters.
Thoughts, rejections, additions.... ? better data ? better logic?
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Originally Posted by dtknowles
