What I have found are:
A known accurate gun
A JHP bullet of 115-124gn bullet
A reasonably slow powder from Silhouette/Power Pistol to AA7 or, reportedly from some guns, a fast powder from Bullseye to 231/HP38
The longest cases you can find. For a single gun where you do NOT load 9x21, you can buy 9x21 cases and trim them to your barrel's head space.
Get a match grade slow twist barrel (say 1:25 to 1:33).