What is considered acceptable accuracy for the .22 pistol? I know for the 45 it has to be < 2.5". The Marvel Conversion claims < 1.8" with most commercial ammunition, is that an acceptable standard for Bullseye?
1/2 to 3/4 inch at 50 yards (at worst, not average) has been the general rule for .22's in NRA bullseye competition for decades. I've seen test targets fired with Hi Standards, Jim Clark converted Rugers and S&W 41's from machine rests down in the 3/8 inch range; equal to what Hammerli free pistols would shoot.
Wadcutter .45's should shoot under 2 inches at 50 yards as should .38's in that configuration. And service .45 full power ball ammo should shoot under 2.5 inches.
One thing newcomers to bullseye pistol shooting often don't realize (such as I did when I started) is accuracy is in second place compared to how good the trigger is. Handgun triggers must break clean and crisp, have minimum overtravel (backlash) and be very repeatable for each and every shot. Back in the 1960's there was an article in a pistol magazine about SFC Bill Blankenship winning the Nationals and setting a centerfire aggregate record. He had a choice of three different .38 AMU pistols to shoot; their accuracy from machine rest at 50 yards ranged from about 2.3 inch down to 1.5 inch. He chose the least accurate one because it had the best trigger.