I recently worked on stocking up a relatively long barreled pistol. I found myself using an adjustable prop, that I use all the time on rifles, at times with the pistol. I don't have a photo of it, but it's basically just a leather covered piece of wood that is attached to an adjustable pipe stem with a heavy chunk of steel at the bottom for stability. It's a tool I wouldn't work without. Simple and effective. Actually, a second one would be nice to have as well.
Jim