Bio-man, Regarding the NSA .25cal slugs, are all of them that you are using - Flat back or Dish base?
I have a moded 25 cal. with the FX Power plenum kit using a 700mm slug liner.
I have tried the NSA FB 33.5 and FB 29.0 with no luck regardless of reg. and hammer spring settings.
Only head way I have made with the NSA's is the FB 29.5 gr at 940fps which will literally shoot hole in hole from 7yrds to 40yrds beyond that range the grouping opens up to a 4" plus erratic cluster no matter what tune I try. I have yet to try the 36 gr. (Note: Reg pressure range tried 115 - 140Bar).
NOTE: I also shoot the MKII's with this setup and they are tack driving from 7 to 100yrds at 940fps. (reg. pressure 115Bar)
I do pest control and would rather shoot hollow point slugs over pellets as the terminal devastation is much greater.
Thanks in advance.