This is quite an interesting discussion, and I'm genuinely trying to learn something here.
Assumptions. Yes, the mother of all buggar-ups. I assume you are overstressing your gun at 20-26 thousand PSI and you disagree. Why do I think that? Because modern, 12-gauge nitro loads intended for modern steel breech loaders with space-age cushion wads and reinforced case heads the pressures for 2-3/4" shells are limited to 11,500 PSI. Some of the black powder loads discussed here are 2.5 times that much pressure. I don't know why this doesn't concern you, but would like to know. The vented breech reduces pressure, but how much? I cannot determine that. Perhaps someone else has?
Several people here have found good reason to use finer granulations of powder for their hunting loads, mainly because it seems more effective at cleanly killing game. I am trying to discover why that is so.
A few things that would aid the discussion:
Looking at expansion ratios and modeled pressure curves for the various gauges, it does seem to me that the bigger the bore, the more benefit would come from faster-burning powder from an efficiency standpoint, yet the trend is the bigger the bore, the larger the granulation. Cannon take powder granules the size of small gravel....but why? (I know why, it has to do with keeping pressure levels safe with payloads weighing pounds, a pretty simple mass vs. acceleration problem with a propellant that generates pressure very rapidly. It is not a matter of efficiency or muzzle pressure but purely keeping the gun from exploding).
Assumptions. Yes, the mother of all buggar-ups. I assume you are overstressing your gun at 20-26 thousand PSI and you disagree. Why do I think that? Because modern, 12-gauge nitro loads intended for modern steel breech loaders with space-age cushion wads and reinforced case heads the pressures for 2-3/4" shells are limited to 11,500 PSI. Some of the black powder loads discussed here are 2.5 times that much pressure. I don't know why this doesn't concern you, but would like to know. The vented breech reduces pressure, but how much? I cannot determine that. Perhaps someone else has?
Several people here have found good reason to use finer granulations of powder for their hunting loads, mainly because it seems more effective at cleanly killing game. I am trying to discover why that is so.
A few things that would aid the discussion:
- How much pressure is generally accepted as safe for each gauge of vented-breech, muzzleloading shotgun using black powder propellant? Is all this concern of overpressure much ado about nothing?
- How much pressure is decreased by the flash hole venting? What size flash hole is being used?
- Is pellet velocity the determining factor for lethality, and if so, is more always better?
Looking at expansion ratios and modeled pressure curves for the various gauges, it does seem to me that the bigger the bore, the more benefit would come from faster-burning powder from an efficiency standpoint, yet the trend is the bigger the bore, the larger the granulation. Cannon take powder granules the size of small gravel....but why? (I know why, it has to do with keeping pressure levels safe with payloads weighing pounds, a pretty simple mass vs. acceleration problem with a propellant that generates pressure very rapidly. It is not a matter of efficiency or muzzle pressure but purely keeping the gun from exploding).