The power of the M4, SCAR-L, G36K and ACR is their ROF and accuracy. Keep yourself aiming at the chest and you'll generally get a headshot kill quickly. If not, it only takes 2-3 bullets to take someone down ... honestly, if you have no problem with the Mk14, then the issue won't lie with lag - you need to adjust to the guns. Too many people stick to one weapon and don't want to learn another, but it could take some time to adjust. Hell, going from the SCAR-L to CM901 took me some time to adjust, I thought the CM901 really sucked.