I have a "single side" holster I've been wearing for about a month. It has one wide strap holding the weight of the gun on your shoulder, with an elastic band around the other arm to keep the strap from sliding off. So far I've been very happy with it.

I also have a conventional "X type" (Galco Miami Classic) I've been trying to configure for a different gun. The X holsters really want at least an offside tiedown strap down to your belt to keep the gun from pulling the whole rig over to the gun side. For various reasons I can't use a tiedown strap, so I've re-rigged the offside straps to go tighter under the armpit to keep the rig from sliding off the gun side.

I used to laugh at the guys who had two, three, or four magazines, handcuffs, etc. dangling opposite the gun, but now I understand; the ballast evens the weight out to keep the gun from shifting. Even the dual gun rigs make sense now.

The single-side rig puts all the weight on the outboard edge of my shoulder joint; even with an aluminum-framed .38, the weight is noticeable. The X rig strap runs diagonally across my collarbone; there's more contact area, and it's closer to my neck. A full-size .45 is less noticeable than the lightweight revolver.

If you wear your shirts tucked in and use a belt, tiedowns are the way to go. If you can't use tiedowns, accessorizing to balance the weight can help.