i dont find anything cool in him using god knows how many different kinds of m4, he should stick to the weapons that suit his character. and that m60 holds one hundred rounds, they fire in three or four round bursts, so thats about forty to fifty kills worth in a single belt. he can control its recoil and reload it very fast. The m60 is his weapon, has been since he was in Vietnam. As you said hes a soldier, but hes a vietnam soldier, hell use a vietnam soldiers weapon.
The m60e3 machine gun: smaller version of the m60, easier to carry under his coat.
A pair of ka bars, so he can just cut loose every so often.
And thats it.
Keep him away from "prefferred calibers" and all that military jargon and tactical crap. He doesnt need the latest m4 with rail attachments to be the punisher. He stands his ground with a machine gun and starts killing. Thats all he needs.