What I found is that once a rifle/pistol/grenade spree medal is earned, followed by clean melee kills, the melee kills would actually provide the ranged weapon applicable medal. It is easily a way to pump up some score. Simply avoid going serious melee until having obtained a ranged weapon spree medal which could be upkept with each further kill, without time limit, which is typically until being hit by an enemy. Watch out for SMGs, rocket launcher and lascannon - excluding sniper rifle I believe, though uncertain about that - since they fail to provide any spree medals, belonging apparently to unclassified weapon categories in the game.
I do think that melee should have own spree medal counter, like "warrior", "berserker", "slayer", "harvester" and so on. Also laser and missle launcher could be linked up to heavy weapons category, with separate spree line. Sniper rifle is - or at least should be - simply a rifle. Even shotgun is considered a rifle class in the game as far as I am concerned. SMGs for the sake of classification could be rifles as well. I mean, it is just fair to have a spree system if to be consistent with a gun or way of attack, otherwise it makes some weapons arbitrarily less efficient scorewise to others.