I'm new to the PCP game and have only a stock Marauder. I was shooting the H&N Baracuda Match (21.14 gr, 840 fps) very effectively, but I was intrigued by slugs and wanted to find a heavier ammo option. I took Nick's advice and bought some samples of the 23 gr slug. The .2165 shot a single hole at 20 yds in my testing and shredded a 3/4" plywood board (did not chrony it yet). Took to the forest same day... one shot (24 yds), one neutralized squirrel, slug did not exit. I thought, OK, that's pretty good. So, I setup a "9-hole" airgun target course around the house with those little 2" adhesive targets (highly recommended fun!) and just took two shots (22 yds, 36 yds)... both went right through the center dot on the target (nice clean, round holes). Shooting groups is important, but when you can take a single shot at a target (paper or pest) and put a slug through the center, that's as cool as it gets. I just ordered 350 of the 0.2165 slugs... perfect accuracy out of a stock Marauder, great heavy projectile for neutralizing ground squirrels, and quiet!