well, the 10.5 grainers didn't give any advantage for longer range accuracy in the two rifles I tested them in; a Rapid and an RM8, and coupled with the reduced ME, they are probably not a goer for these particular rifles.
The rapid grouped 5/8" at 40 yards with JSB 8.4s, a fraction more with JSB 10.3s, and just over an inch with the slugs
Similar story with the RM8, except both JSB variants were around 3/4", and the slugs were around 1 1/4"
There was a very light breeze swirling around, but just the normal level that you expect in real world field conditions.
My phoenix is actually a .22 (I forgot), but I do have another Rapid in .177 I'll test with, although it has a tightish choke so probably not idea for a solid slug either.
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.