I am new to cast bullet reloading (been reloading for 11 years) and have a question about bullet size and accuracy. I am loading the 330gr Beartooths sized .452 in my 5.5" Ruger Bisley .45 Colt. Load is 22.5gr H110 for a velocity average of 1199fps. I have installed a Belt Mountain #5 standard size base pin in the gun. I am not seeing the accuracy that I think I should. My best group at 25 yds with this load is 2.3". I have gotten 1.5" groups with a 250gr bullet from another manufacturer at around the same velocity but leading was a big problem. I have read that the Rugers have max spec bores and throats so I was wondering if going to a .453 sized bullet may help with accuracy. How would this slight change affect pressures and velocity?

Slug your bore and cylinder throats to determine what the diameters are. Cast bullets seem to work best at .001" - .002" oversize to bore. If the cylinder chambers are smaller than the bore, they need reamed to be just slightly larger than bore diameter - the aforementioned .001" to .002"

Gas checks may help with the leading problem. 1200 fps is fairly fast for .45LC cast bullets coming out of a 5.5" bbl. How's accuracy if you back off a bit?

Throats on new Rugers almost always need reamed. I'd definitely check that first.

I too use a Ruger Blackhawk in 45 Colt and sometimes shoot some of the realy hot loads also. I had a gunsmith friend of mine ream out the chambers as they were tighter than the bore (ya ever wonder why they do that) and of course made the slugs less than bore size. He also recut the forcing cone a bit and then polished it. These 2 simple things made a world of differance in the accuracy of mine especially with cast slugs.