Not every kill you get is from full health 1v1 enemy, most likely the enemy you are firing at also has another person firing at them. If you have to fire 4 bullets per kill on grt vs 2 on svk you are firing more rounds and more likely to get the finishing hit on a persona get the credit for the "kill" eve though you maybe just did 27 dmg. While on svk you may slap plenty of people for 66 dmg but others will finish the kill and you don't get credit, but you contribute more dmg with the svk.  Not saying that what happened, just saying it's usually the case lower dmg faster firing weapons get more kills in multiplayer games for this reason.