So went out to the range at first light today with my two Maverick Compacts, 30 cal and 22 cal. Both with the 500mm barrel STX. Shot the 30 cal first and zeroed it at 50yds and adjusted 883fps on PW6. Checked Strelok Pro for 100 yrd shot and adjusted scopt up 12 MOA and hit the 100 yrd bull's eye on the first shot. All my shots were with the JSB 44.75grn pellets. Now here's where things went off the rails. Swung my 22 around and shot the 18.13grn JSB's at about 893fps and basically tac driving at 50 yds. Then I decided, to put the 700mm barrel on and shoot 30grn .218 javelin slugs and at the same settings, my velocity dropped almost 300fps. I was under the impression that the slugs being shot from a longer barrel would have more time to accelerate and be faster than the pellets coming out of the 500mm barrel. Tried bring the fps up with the HSA and maxed out at 750fps and could not cock rifle on PW7. Tried higher reg pressures same issue. Backed HSA back down then gradually came back up making only quarter to one eights turn, sill no difference. So measure the pellet diameters vs the slug diameters and found that all pellets were significantly larger than slugs at .226 vs .218 or less. One thing I didnt do was shoot the slugs from the 500mm barrel. Also, the porting on the compact barrel vs the sniper barrel is considerably larger. The compact barrel has both the slug bridged port and the pellet port. On the sniper barrel, the porting for both is smaller than the compact barrel and there is no bridge on the slug port. Anyone have any advice, much appreciated.