For my E-Mag: Medium spring, #2 carrier, 2 shims, 850 preset tank. Had the 2.5 carrier work, but it was leaking down the barrel more often than not. Still feels a bit heavy on the bolt movement (used my finger, not brave enough for the tongue - besides, that powerfeed would be sure to entrap my tongue if there were any mechanical failure....) so I'm not quite through playing with it. Ran some old oval paint through it, stuttered now and then, but didn't chop a one!