I tested today the .251 and .250.
I did not adjust the power on the gun. I shot tethers at 2350 psi. This what giving me 815fps with the 58.4g slugs. That's 86fpe. and I only have 2 turns in with the power adjuster.
No I shot from 40 yards:
8 shots with .250. There are 4 shots in the bottom group
5 shots with .251
One thing to notice. I have to get used to holding the gun. It has a bit of recoil from the hammer. I bet I can do better with both groups. I'm just wondering what size to order from Tom. The .250 shot a little faster but they opened up a bit.