Looks like we all have similar experiences with the .45 ACP in revolvers. I have a 25-2 (1955 Target) like Terry's...6-1/2" pinned barrel, N-frame. It's a big gun that shoots SMALL groups...my best ever at 50 yards: 1-7/8" with five in one hole...iron sights. I also shot a possible on the NRA silhouette course with it once...in practice <wince>.
My Ruger Blackhawk convertible groups the 200-gr H&G bullet in an inch and a mite at 25 yards. The ACP cylinder is just a bit more accurate than the Long Colt wheel...just a BIT.
I think the long barrels are a factor. My Blackhawk is a 1976 gun, and has properly sized cylinder throats and has had the forcing cone chamfered which help accuracy considerably.
The 1955 Target also shoots the Long Colt 260 gr. bullet, in Auto Rim cases, very well. A heck of a plate or pin load with lots of smash. I use the Skelton recipe that he called the 'Poor Man's Magnum' and 'the flying shotglass'.
I don't understand why prices on nice old 25-2's are hanging at around $400...I wouldn't take twice that for mine.