Higher velocities ALWAYs come from higher pressure. If Swiss gives 1,200fps, it does so at the same or higher pressure than GOES when producing the same velocity.
: I expect a velocity of 950fps to 1,000fps might be given to the heavy slug, maybe not, at safe pressures for 'normal' shooting in the thin-walled double gun.
: The round ball may be pushed to 1,240fps to 1,300fps with safe loads, giving the same pressure as the slug's max load. The ft. lbs energy of both projectiles will be the same with identical pressures, as happens with ctg. rounds we are familiar with today. At a given pressure, all bullet weights, shapes and sizes produce the same ft. lbs. energy from THAT gun. Within game shooting ranges, that which gives the highest velocity will also give the flattest trajectory. Slugs take over in trajectory beyond hunting ranges as in over 200yds.
: I do dislike foot pounds energy as a representitive of killing power as it is a poor method of judging killing potential.
: I would rely on 3 dram loads (82gr.) for shooting game sized like deer out to 100yds., but prefer a bit more steam for flatter trajectory and thumping power on larger species.
: In large bore guns, the round ball will give the flattest trajectory and highest striking power for any given powder charge. This was proved back in 1850 is needs not to be re-proven today.