I've seen good group sizes with my Evol .30 with all NSA slugs around the same weights as the JSB pellets. It is tuned hotter and shoots Hades 44.7 grain pellets 940 fps and the Heavy 50.15 grainers at 915 fps. Slugs of this same weight range shoot equally well with my set-up, but a little slower because of the additional bearing surface area over pellet skirts. Your best bet would be to order a box of each weight of NSA slug, a tin of each JSB pellets, and the FX Hybrids, the Varmint Knocker slugs on eBay to see what your gun likes with the factory tune. With Tom's attention to detail in manufacturing these barrels, you can't go wrong with most meduim weight projectiles. I would not mess with the regulator setting for efficiency sake if wanting to go with slugs. The hammer spring tension screw can get the most out of the valve and barrel for both pellets and slugs.