I've been placing the gunbelt and holster above my pant waistline, (holster bottom over the pants rather than in the pants), against my skin. The belt buckle either covers or is just below my navel. I rely on the length of my untucked shirt to conceal the bottom portion of the holster.
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I'm carrying a full size SW M&P9 in a Comp-Tac Minotaur holster, and I'm 5'8" 150 lbs.
Wait ...
what?
The gunbelt goes in your belt loops, the holster goes on the belt and in/on the waistline as designed, and the gun goes in the holster.
Why in the world would you use a gunbelt as a belly band? What "gunbelt" are you using, how do you draw from such a setup, and what lotion do you put on the rash you must be getting under a leather gunbelt right on your sweaty skin all day? Or is this a "just going to get the mail" setup?
Here is the way I carry, the setup has evolved a bit since these pictures, but the basic concept stays the same:
http://thehighroad.org/showpost.php?p=5947477&postcount=15 (more detailed text and more pictures in that post from a while back)
Undershirt is optional, but I prefer to not be chafed by the rough inner leather.
So you put on underwear and undershirt, put on pants and leave them unbuttoned, thread through the belt in the provided loops, attach the holster to the belt*, drop the gun in the holster, apply overshirt, put on socks and shoes, and go about your business only wearing one belt and with coton between you and the non-porous belt.
The only time I wear a second belt is when I'm motorcycling in very cold weather, and the second belt goes in the overpants, with the gunbelt and holster on the normal pants
again, what drove you to use an IWB holster and pants belt as a belly-band?
* (some require threading the belt through the holster, I prefer clip-type holsters with offset clips)