There are several tools available from Brownell's for the job. 2 reamer sets: one is .4525" with a set of pilots, which costs $115; the other costs $200 and doesn't say what the size is. There is also the cylinder hone, for $30 or so. Polish the chambers and the throats together. I have done this on several guns and I use a bullet of the appropriate size as a gage. I have opened mine to about .4515." That seems to work well for me. I would be concerned with the dowel with making the cylinder throats less than round. Don't forget the barrel forcing cone. I cut my .45s with an 11 degree cutter. It cleans up what can be a rough forcing cone and makes it concentric with the bore. I have seen them pretty far off.