That's assuming the bore is concentric with the O.D at the muzzle and the grooves are all the same depth , they're very often not. A Powely gauge will do it for you as well as a tri-mic, the later is a specialty and rather expensive tool usually found in a machine shop. The Powely gauge is a rather simple V tool that can be machined and is used with a bore slug to measure lands and grooves . It works with even or odd numbered rifling as long as the orbit/radius of a (slug groove bottom) can be contacted with a mic or caliper. Remember the land on a lead bore slug is the groove of the barrel bore.
I've never measured any production revolver of any make that had all the chamber mouths the same diameter either or even perfectly round. I've measured some that were as much as .003 difference if memory serves me correctly. Plug or ball gauges are the tools of choice for this job. Caliper jaws are only a rough measurement but will tell if out of round by cross mic-ing.
Yeah, that works as well. I machined a Powelly gauge so that is my go to for bullet or bore diameter measurements , very accurate tool !
The lead slug driven through the bore will tell you the tightest spot it has passed through but not necessarily what the muzzle is which very often is the largest part of the bore. Quite often solid frame guns will have bore tightness under the threads. This is where a set of plug gauges really pay for their keep and yes it can be hand lapped out with cast lead, lap charged, bore slugs on a bearing-ed lap rod. I once tried fire lapping a percussion revolver and it did not work for me although I have gotten very good results from the process with cartridge guns.
Just describing some of the tuning and testing process I use for my NMLRA / NRA match guns...I only share the process and tech that has helped me win national championships and set national records. Not here-say only proven end use results published on the record at NMLRA.org...c
I too have spent many years competing in NMLRA events at the local and territorial level and have found that really good shots will win even with average equipment as most of these guns from the factory now days will demonstrate accuracy superior to what there owners will be able to achieve with them. The tuning makes it easier to accomplish but usually the inherent accuracy is already there it just needs some tuning help to better reveal/manifest itself.
I agree 100%...The shooter makes a far greater contribution to his match results. On the tech side a seemingly small mistake like using too firm of a revolver lube due to cold weather messing up accuracy could cost a few placements in a match. Even a frequent dominator of matches many times only wins or loses the gold by one point or X. Those few shooters go to great lengths to be sure they are using the best equipment and tech...c
That’s awesome! I would love a BP revolver I could shoot bullets out of. I cast for a lot of different calibers.
This is true, and i can make the tools i need, but most can't. My reply was for the less advanced shooters. Those that have the proper tools should definitely use them to get the absolute most out of their guns.
