Has any got access to real BP pressure curves ?

[mehavey]

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?

[Hawg]

Maybe this? http://www.texas-mac.com/Black_Powde...bturation.html

[mehavey]

Driftwood Johnson's Post in [Brand-X] three years ago begins to address it as well. 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 -- and gives significant advantage to smokeless for cast bullet shooters.

Thoughts, rejections, additions.... ? better data ? better logic?

[Hawg]

Originally Posted by mehavey

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)

I can't tell you anything about pressure curves and peaks but I can tell you from experience that 80 grains of Swiss with a .54 caliber solid, pure lead bullet will strip the rifling and tumble leaving the barrel a leaded mess in a breech loader.

[mehavey]

You talking Sharps ?



In all my N-SSA days, no problem at all -- pure lead [a little hard on the shoulder with that steel toed carbine though)

[Hawg]

That was not the case with my paper cutter Sharps. I used clip on wheel weights with great success but pure lead was a no go.

[reinert]

I use only b.p. in my three B.P.C.R.s, and haven't a clue on pressure data comparisons between the new and old propellants. There's so many variables to consider when I started to think on your question, mostly on obturation. Maybe I'm on the wrong track here, but these are a few variables I thought of that would have an effect on obturation, while using a properly cast bullet:

Barrel length
Alloy mix
Bullet/bore diameter (sizing issues)
Bullet lube (shooting a greaser in all three of mine at present)
Paper patched bullet (compared to a greaser?)
Powder charge
Primer (standard or magnum)
Annealed cases
C.O.A.L. (bullet engaged into rifling, or set for some freebore)
Leading issue (too hot a charge needs to be considered? What's the thought here, 1250 f.p.s. max to keep leading in check?)

Probably more factors than I've thought of here, but I think they may all have to do with chamber pressure, affecting obturation. There was a guy on the old "Talk Shooter's" website years ago who would shoot test rounds into his swimming pool to see what his bullets read as to size after leaving the muzzle. He thought it was a good way to catch a bullet for measuring without too much deformation of it; don't remember the conclusions or comments from back then. Our local range has a 200 yd. berm of fairly soft material I can retrieve bullets from, and though the noses are always deformed, I sometimes get pretty decent bases to look at. Mosty, I look to see if there's any "finning" on the base pulling off the rifling. I haven't had any of that with any of my rifles, though I know it's a rather crude observation at best, my bases look pretty good, and I'm quite well pleased with the accuracy on all my rifles using black powder exclusively.

I know folks duplex their loads, but that's kind of a fouling issue preventative mostly, no? That, too, would be an obturation factor I would imagine. I guess I'll just stick with the black; don't think any of my loads push past 1200 f.p.s. I do get some leading, but it's quite manageable. I use a 20:1 alloy in all my B.P.C.R.s. Seems to work very well for me.

[bladesmith 1]

If whatever you're shooting is accurate, why would it make a difference which one is fastest ? There's a reason some people like shooting smoke and it doesn't have anything to do with pressure curves. I'm sorry if I sound like a sh!!head. Just don't understand the why of the question.