Do yourself a favor and read the article in the link. If you don't know someone in your area with a pin gauge set then shoot me a PM. I see your in Alaska part of the time. I have a set and would be happy to measure your cylinder and bore for you.
The cylinder mouth and groove diameter dimension are the first critical dimensions you need to determine before you fire lap your bore. If the cylinder mouth is not one or two thousandths over groove diameter then you need to correct that first. Otherwise you're wasting lapping bullets and not doing your bore any good.
I have one of the Bisley Flat Top 44 Specials and the cylinder mouths were all .432 and the groove diameter .4295, so it won't need the mouths opened. I haven't lapped it yet but will this winter. I wouldn't be surprised if yours measured with similar dimensions but you still need to check.
Check out this article. Great information.
fire lapping 
