I believe Aero Precision makes lowers for Surplus Ammo and Arms. I have an SAA and am happy with it. Good quality for the price. Spend your hard earned money on a quality upper and trigger. The lower only looks pretty.
I use Hornady 55gr FMJ boat tails because they're cheap and a helluva lot easier to load than flat bottoms. I've been really happy with accuracy as well. My reloading rig doesn't flare the neck enough to seat a flat bottom without it falling out, so I stick with BTs.