Is there any room left at the end of the cylinder after the compression stroke? I had seen online about adding material to the end of the piston on the FAS 6004 to increase compression on SSP's, some had used epoxy resin but I used three layers of aluminium tape on my Sig Sauer ASP Supertarget, which has the same powerplant.

It is a fine balance to avoid causing it to dead-head and strain the mechanism by adding to much, but it did make a definite improvement to the fps. I also swapped the piston and breech o-rings for x-rings, but saw no benefit.

The other risk is making the last part of the stroke really difficult, but I don't think the P17 needs any MORE resistance in that area!