I just measured the chamber throats on my 3 Colt "CIVILIAN MODEL OF 1917" examples and they all showed to be right at .456".

These were produced/delivered in the early 1930s in a very few numbers (approx 1000) and were in a very narrow serial number range.

Once again I feel the industry standard of yesteryear was for the chambers to be a few thousandths larger than the fmj ball bullet's diameter........for whatever reason.

Maybe the open base fmj bullet of that time obturated enough so that it wasn't an issue back then. I have read where the M1917 revolver was more accurate than the M1911 and during competitions with both being used they would have to spot the 1911 guys a few points to even things out.....so accuracy couldn't have been considered too terribly bad back in the day when using ball ammo.

Now when using modern jacketed hollow point bullets with a fully jacketed base it could be that they don't obturate as much if any at all. I could also see soft lead bullets in the .452" diameter giving not-so-stellar performance either due to the shallow rifling and/or larger chamber throats. Most people consider either softer hollow base lead bullets or .454"-.455" harder lead bullets to be better suited.

I tried "plated" hollow base bullets once but the added hardness/thickness of the plating did not allow the hollow bases to open up as expected at "normal" velocities and when I pushed them faster they simple shaved over the rather shallow rifling of the M1917 I was using for testing......so accuracy either way wasn't as hoped for. When I went back to 230gr fmj bullets accuracy was right back to being very good.

Dale