I measured my son's 307 brass against fired 308 Win. brass. The large 30-30 rim's extraction groove lets the top extractor of the first Win. 307 carbines grab the rim, solidly. The downside is that there's so thick of brass around this extra wide groove, that it only gives this case the equivalent internal volume of the old 300 Savage cartridge. So it's only a 300 Sav. number. Ackley suggested using a 300 Sav. magazine spool for his 250 Ackley Imp. cases. A 22 version would be the 22-250 Ack. Imp. No slouch, but do you really need that semi rimmed case, when the old 220 Swift cases are still out there. My last purchase of cases for my son's 307BB, carbine were made for the 356BB. The 307 has become a real orphan, in spite of it's being a really neat woods rifle. JMHO.Being a rimmed cartridge, I did all calibers on the British 303 case, and the performance of the smaller calibers was quite dissapointing! The 307 Winchester and 444 Marlin were and are to of the best cases to work with!
Variations of the 22-307 would, depending on the barrel, bullet and load, easily reach 4,200 to 4,500 fps. with superb accuracy.
Running the 22-307 Improved with a 1-7" twist and 80 gr. and heavier VLD bullets, it's 1,000 yard accuracy has proven to be quite phenomenal to say the least.