I just recently purchased a ruger blackhawk in 45 colt, with a 4 5/8 barrel. I have heard that the blackhawks in 45 have undersized cylinder throats. I have tried to push some lead swc (.451) down the front of the cylinder and they will go with some pressure from my thumb. But have some 300gr xtp's (.452) and they will come no where close to fitting in the cylinder. The nose of them will hardly go in. I had loaded the gun fairly hot I guess. 19.0 gr. of H4227 with the 300gr xtp. And shot it before I noticed it, and it shot fine, with 1 in. groups at 20 yards. But now I'm worried that when loading it to +p, the pressure's will climb rapidly with the undersized cylinder. Is this true? Anyways I got the information for cylindersmith.com, and I was needing to know if I should mess with it or not, because alot of you have more experience with this than I do. So any help would be greatly appreciated. Thanks. Andrew.