From what I have read, most modern Colt's have a .451" groove diameter, and .455-.456" cylinder throats which is not ideal. I have been shooting .451" Goex 235gr bullets from Powder Inc. They seem to shoot pretty well, but on this last trip my cylinder and barrel took some heavy leading. So I am not sure if it is because the bullets were undersized allowing hot gas to pass the bullet melting the driving bands, or if it is a lube issue. Powder Inc. only offers the Goex bullets in two sizes, .451" and .454", which is still too small for a modern Colt cylinder. I have not measured the throats on my Colt as of yet, but will do so when time permits.
I read a threat elsewhere, where someone asked Colt to build them another cylinder with a removable bushing, and with .452" throats. Colt did this for free, however, the throats were still the standard .455".
Jared