Quals to 500m are a bit different than the targets we put out for 3Gun. 3 to 4 MOA is usual, once in a while a tad smaller. A2 sights are fine, but you will want to have a target front post thinned to a bit of a point. 20" barrels are fine for Limited Irons provided you put a sight block right behind the comp to take advantage of the sight radius. 300 yard zero and 55s or 60s at 3100 fps will be just fine. Regardless, you will want a free float hg. Most 3 Gunners opt for 1:8 twists as the 1:7s tend to pop jackets on the cheaper bullets once the gas port starts to erode out.

Now, the real opinion...don;t buy anything. Come out to a few matches, bring some ammo and try some stuff out. 3Gun is not cheap, and buying gear before trying it is an expensive mistake for many. Come out to CRC on Saturday for the USPSA pistol match. There will be a few of us out there practicing for SMM3G and you can get some free wise counsel in person.