I've been tinkering with mine when time permits. With the reg set at 125 it shot ZAN 33gr HP good, NSA 26.8gr good, one hole groups at 30ys. Easily did 1.5 inch groups on my 115yd target. Bumped the reg up to 145 and pretty much stayed the same with the assortment of slugs I have right now. Went to 160 and lost grouping with the ZANs and lighter stuff. Groups quite well with an NSA 33.5gr HP flat base slug I have and might be able to MOA with that one were I to try it.
I've seen that these like the heavier boat tails more than flat or hollow base slugs but haven't tried any yet. Sticking to flat mostly as I have a swage kit to make them once I get time to set it up. You Tube Channel called My Airgun Range. Extra long range shooting, pushes one out to 500yds if memory serves using heavy boat tails.
The hammer spring adjust doesn't do much for velocity once set but it does affect it. Enough so that one should be able to find potential sweet spots but again that's something I need time to mess with on paper over the chrono.
