Personally, I wouldn't run the 40gr. Stick with 27.5gr - 34gr find which diameters works best for you. Make sure you clean your barrel as soon as you get it. If you decide to run a heavy liner, which you will need to shoot the 34gr+ slugs hot, I suggest polishing the liner. It will help with your liner not getting fouled as easily or quickly. I had a mk2 700mm with the power block, power plenum, shooting 30gr javelin slugs in 217 and 218 at 960fps with the reg sitting at about 142ish bar. No heavy hammer, no slug kit, no tensioned barrel. Just a heavy liner, huma probe, huma transfer port and hunterTACtical co magazines. If you go through some of my posts, you'lls see iguana kills beyond 150yds.