29.5 neilson in a .25 fx impact?

I had good luck with the 36,2 gr in mine , I never tried those , what speed you shooting them ? the 36 gr shoot fine at 970fps ,

My Crown and Impact love the 29.5's in the 600 superior liner @ 960 or so

You could probably adjust up or down to tune the velocity to what that pellet likes. From what I've learned you have to imagine a wave going down your barrel when the hammer strikes the valve. The wave has peaks and valleys and you goal is to tune it so the projectile leaves the barrel at the point where this wave has an amplitude of 0 between the peaks and valleys. When you are adjusting velocities this is what you are trying to do its one way to harmonically tune a projectile to a barrel. But since every barrel is slightly different its hard to say an exact velocity where this will happen for your barrel without testing.

I shoot 29.5 out of my Wildcat MK3 @ 970 FPS with 700mm barrel. My buddy shoots 29.5 out of his Impact MK2 @ 980 FPS with 700mm barrel. We shoot out to 150 yards no problem.