R.M.,
IDEALLY, your choice of bullet diameter is driven by actual barrel groove diameter. If you haven't slugged the bore, your just guessing. Most of the current available .45 Colt will be either a nominal 451 or 452. IDEALLY, again for a 451 barrel you would want bullets sized to 4515 or 452. For a 452 barrel, you would want bullets sized to 4525 or 453. However .... 454 will work just fine in either. Unless your pushing maximum pressure 454 vis 452 won't give you dangerous pressures and if your shooting BP, no worries.
The problem is the cylinder throats. Tight cylinder throats can give you excessive pressure and excessive felt recoil. Just to cover Bibbyman's comments about his Rugers, Ruger is famous for undersize throats. Not just tight, but UNDERSIZE. Common to find throats in Rugers with a 451 bore to have cylinder throats at 448 or 449. Not so Bueno.
So to pick an appropriate bullet diameter, first need to find your bore diameter and size accordingly. However, you'll probably have no worries with 454 lead bullets. You may notice some excess felt recoil though.