Tuning FX Wildcat mk2 questions.

I am trying to make a .25 cal slug shooter. I have installed slug barrel, Huma Air Reg and plenum. What kind of velocity can I expect to get 34 gr Knock Outs going?

Another question. While shooting yesterday I suddenly started hearing the hammer spring make a twang sound. It seemed velocity maybe went south but I ran out of time to check with a chrono. I did have some hammer binding which I thought I fixed by polishing with fine grit sand paper. Any thoughts.