This is all quite interesting. My own 12 bore testing has been with round balls .684" at 480gr. in pure lead and 466 gr. in WW metal, as well as .715" at 545gr. in pure lead and around 520gr. in WW metal.
: My accuracy results were good in a side by side with 26" tubes. I shot only one large deer with them at 100 yards. Of course, there was a 3/4" hole in and out.
; I used special wadding to keep the balls centred, so they would be fairly accurate. I achieved 8" groups at 100 meters, 2 lefts 2 rights. This was using both the original-type BP loads as well as smokeless loads duplicating BP velocities. I found my 12 bore didn't diverge with heavier loads, nor did it cross with lighter ones. I tried to keep velocties in the 1,500fps to 1,550fps range for the full power ammo, but the ligher load shot well too.
: Since doing some disapointing minor penetrative testing with the hollowbased slugs, I switched to round balls. They penetrate and don't break up, even the 13 brinel ones of WW metal. For expample of possible penetrative power, S. Baker stated that a hardened 14 bore ball would pass through and through an Indian Elephant's head using but 4 1/2 drams of powder. That's good enough for me. The 150gr. and 191gr. charges duplicated light and heavy BP African 12 bore loads. The light 12 bore load, listed in Greener's book was 110gr., however I used his velocity figures of 1,384fps and 1,584fps as a base in developing my own duplication loads, BP and smokeless. A 110gr. charge in my double made only 1,200fps. Greener's 12 bore lower velocity was achieved with 150gr.in my gun and the higher velocity, with 191gr.2F. Both shot well and to the single leaf + Point blank sight I installed. As well, smokeless loads did likewise & had about 1/3 the recoil.
; Any solid conical cannot be shot in a smooth bore with accuracy, unless it possess some sort of guiding system, as in attached wads, or being hollow like a foster slug, utilizing the weather cock principle. Rifling on the side of the slug has no observable effect in rotating for accuracy. Foster slugs I've recovered from soft materials have shown virtually no 'rifling' left on them, due to slugging up in the bore and wear from the bore as well. Lyman itself states the 'rifling' on slugs is so they'll compress in a choke without damage, only. For air to turn or rotate the slug, the passage in the groove must run from one end to the other, not be closed off by lead or wads as with rifled slugs. In the late 1800's and early 1900's many different methods were tried to get slugs to rotate, but none were very successful except for rifling in the bore, in one form or another.