need info on burn rates for

[madcatter1]

Does anyone or has anyone found a burn rate equilivate between ff,fff,and 4f.
i make blackpowder shot shell to shoot out of a centerfire singleshot pistol for rabbit hunting and the problem i am having is i want to decrease the amount of powder to add more shot in the shell.
I assume that 4f would burn quicker and take less space in the shell but i dont know how many grains of 4f equals the same burn rate of lets say 2 f

 

[Stumpkiller]

I drop 6% or so by either weight or volume when going from FFg to FFFg to keep the sighting on, so I assume that relates to burn (explosion?) rates or the energy equivalent and differences in airspace between granules, whatever. So, 85 gr FFg = 80 gr FFFg. Never tried FFFFg as a main charge (nor would I start now).

 

[Joel/Calgary]

Does anyone or has anyone found a burn rate equilivate between ff,fff,and 4f.
i make blackpowder shot shell to shoot out of a centerfire singleshot pistol for rabbit hunting and the problem i am having is i want to decrease the amount of powder to add more shot in the shell.
I assume that 4f would burn quicker and take less space in the shell but i dont know how many grains of 4f equals the same burn rate of lets say 2 f

This is a rather complex subject, because the internal ballistics turn out to be complex. If you examine the published data for muzzle-loaders and cartridges where two granulations are used with the same gun/projectile to get the same velocity, you'll find increases ranging from 10%-55% when comparing 3Fg to 2Fg (or 2Fg to Fg), but always with the finer powder giving higher pressure (where published) for a given velocity. Averaging all that I found, I got about what I read as a rule-of-thumb starting point when I got started in the '70s: increase the charge by about 1/3 when going from 3Fg to 2Fg (or 2Fg to Fg), or the equivalent of decreasing the charge by about 1/4 when going the other way (the ratio of the powder charges is 3:4). Many people have reported using a difference of 5-15% when changing granulations, but I suspect that this may be related to the complexities of point-of-impact mixing in with trajectory/velocity.

There used to be published info for using 4Fg in loading small cartridges or small caliber ML pistols & revolvers, but because of that increase in pressure when changing granulations, many nowadays will take the conservative/safe route of recommending using 4Fg only for priming powder. How are the pressures for your current shot loads? If you are currently using 2Fg, as suggested by your question, I would recommend working up a 3Fg load starting at around 3/4 of your 2Fg charges, with the usual cautions to start low and work up carefully, etc. Always test the patterning & penetration (and the consistency of them), and bear in mind that the sharper pressure increase with finer powder may negatively affect your patterns. I would suggest that if and only if the pressure generated by your 3Fg shot load is WELL within the capabilities of your case and pistol, you could try some 4Fg loads starting at around 3/4 of your 3Fg ones, with the same cautions.

Regards,
Joel

 

[Dphar]

Does anyone or has anyone found a burn rate equilivate between ff,fff,and 4f.
i make blackpowder shot shell to shoot out of a centerfire singleshot pistol for rabbit hunting and the problem i am having is i want to decrease the amount of powder to add more shot in the shell.
I assume that 4f would burn quicker and take less space in the shell but i dont know how many grains of 4f equals the same burn rate of lets say 2 f

The following is contingent on the powder having the exact same components, mill time and compression.
Changes in these things can also effect the burn rate somewhat.

With these things on mind and the fact that BP is a SURFACE BURNING propellant.

FF is twice as fast as F, FFF is twice as fast as FF. FFFF is twice as fast as FFF.

This is based on the surface area of the powder. FF has about twice the surface area of F. Thus it will burn twice as fast.
We also need to remember that BP is NOT smokeless powder and doubling or even quadrupling the burn rate will not double or quadruple the pressure.
But FFFF can cause problems based on a friends experiments.
Elmer Kieth burst the cylinder of a SAA colt in 45 with fine BP FFF I think and 300 gr bullets.
However!
FFFF is too fast for your purposes.

Dan