Adjustable pin probe

Have you tried the NSA 33.5, 36.2, 38.5 HP or VarmintKnocker 34gr slugs? They all shoot .5 to 1.25 MOA @ 100 yards in my .25 Impact with the slug liner A. They shot that well at several velocities from 740 to 960fps.

Also be careful with the adjustable pin probe. If you have ported your barrel port you could run into problems.

https://www.airgunnation.com/topic/the-infamous-slug-power-kit-on-my-gen1-impact/