Chrisman, the Sig P220 Compact you are looking at was my first 45acp. I love the beavertail and the shove of a 45acp. I bought extra mags from Top Gun Supply. P245 mags will work in it as well. As for the DA/SA: Yes, you can cock the hammer back and have 6+1 rounds of SA. You will really like that decocker too. It's a sweet feature. Oh, and those SIGLITE Night Sights. You will more than likely compare all other sights to them going forward. And just wait til you see how well you shoot it...
One last thing: the P220 Compact has a 3.9in barrel, not the 4.4in barrel that Bud's has printed there. I've heard nothing but good things about Bud's Guns but I've noticed that they type the wrong crap in their adds pretty often.
Good luck, let us know after you've been to the range and wipe that silly grin off your mug!
