Haven hunted African plains game and spent some time discussing caliber preferences with several professional hunters along with black powder shooters over there I have been converted to the larger calibers of .58 to .72 for my black powder hunting rifles. Not that my .40 and .50 calibers didnt do the job on 7 whitetail I have shot. It's just that a big round ball punches a big hole with more foot pounds of energy making it a more effective tool for any game weather dangerous or not. My next rifle is going to be a .62 rifle with forsyth rifleing of 1 in 95" twist. The idea is to get more velocity out of this round ball to equal some of the energy figures of some of the popular African cartridges used on dangerous game. Then I have to test it on some big critters.
The twist will not change the velocity at all.
I idea that less friction increases velocity is not correct. Assuming the slower twist significantly reduces friction.
I would not go slower than 70-80 inches.
My 16 bore has 8 shallow grooves, narrow lands and will shoot all the powder I can stand without "stripping".
Normal load is 140 gr of FF Swiss and gives about 1600 with a 1 ounce ball. Forsythe was using 15 to the pound balls so this rifle is very ball park and gives very similar velocities to what forsythes 137 gr load did based on the trajectories he achieved. Remember the British used to increase the velocity of shotguns by ROUGHING the bore close to the breech to increase friction and pressure.
I can get it to 1750 & about 3000 fpe, if thats important, with more powder but its a lot less fun. Getting a 62 to the level of even one of the milder "big game" calibers like the 450-400 NE +- 4000 fpe would be a tall order. A 12 ga ball at 1600 is between 30-06 and 300 win mag. Need a 11-10 gauge ball. At 1400 fps a 1000 gr ball makes 4350. Probably need 200 gr of powder perhaps significantly more.
I suppose if it were possible to get 2000 fps from a 350 gr ball its still 30-06 level for energy.
So getting the energy (which is really irrelevant in the world BP arms) to 375 H&H energy levels, the current small bore "standard" for dangerous game, is just not going to happen. The FPE favors high velocity and thus favors smokeless powder cartridges. A 130 gr 270 will make similar energies to my 160 bore top loads but would be less effective on a angry bear then the big RB would be.
The shallow grooves and narrow lands IS a great feature. The 16 bore loads easy and fouls very little with Swiss.
There s a lot of BS out there about Forsythe rifles, ridiculously heavy powder charges (by Forsythe's standards) and so forth. Make a 62, load it to 1650 or 1700 and quite worrying about the energy figures.
His book is available for online download or reading on line.
http://www.archive.org/details/sportingriflean00forsgoogThis is the second edition. The one John Baird reprinted years ago is the first edition and the one I have.
Shooting large game with MLs requires hardened balls as detailed by Forsythe and John Taylor in "Pondoro".
Dan