I use this one: http://www.stitchsloft.com/loft/scre...-p-90-harness/
the harness really isn't shown in the photos, it just peeks out from the vest. But in the first 2 stargate shows you can see it wrapping around under the vest.. it wears like a manzier. I've hung my g36 off of it and it's pretty cool how much weight it can actually carry. But the price is a bit steep unless you're doing a stargate costume. :P
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.