I'm going to presume you mean repeating handguns as opposed to rifles or single shot pistols. My most accurate centerfire hand guns are both 45 ACP's. Oddly enough I'm not the 45 ACP's biggest fan. For myself the 45 Auto is pretty much ho-hum.
That said these are the two most accurate a Sig 1911 and a S&W model 625. Brass is Remington 45 Auto in the 1911 and 45 Auto Rim in the S&W 625 (Auto Rim to keep it out of the 1911). Bullets, 1911 230 T/C home cast, S&W 625 Speer 200 Gold dot. Powder, both get Tite Group, 4.7 grains in the 45 ACP and the 625 Revolver gets the maximum listed in the Sierra #5 manual under "45 Auto in Revolvers" for 200 grain bullets on page 813. Primers are CCI 300. LOA is 1.71" for the 45 Auto but I didn't write it down for the 45 Auto Rim. Both are taper crimped. I'm a so so hand gun shot, when shooting with the best pistol shot I know after bragging up the Sig 1911, after he put the first magazine through it his reaction was "OH WOW". After the range session he made the first of several offers for the pistol, it's still mine.
