doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 12 ga. Heading Gage

The .729" tells you what size the pilot that is furnished with the reamer will be. This is determined by your bore size, just forward(toward the muzzle) of the forcing cone. If your bore is bigger or smaller that .729", buy the reamer that shows the desired diameter. You can also get other pilots, I have several, and have lengthened chambers in several guns with different bore diameters. I've also made pilots in odd sizes, for odd size bores. You don't need to specify the rim diameter, as all the reamers will be the same, correct size, in that area. My catalog says 184-052-729AC. This would be correct, if you have a .729" bore and want a 2-3/4" chamber. When I bought mine, I bought a couple of "standard" pilots that were larger, so I could make odd size pilots. I don't see them listed, now. Looks like your only choice of pilots(bushings) are .725", .727" or .729". .729" is "standard" 12 ga. bore ID, but yours may, or may not be that. Do you have a bore mic? Good thing to have. If you plan to do any choke opening, you'll need a bore mic, for sure.

Jim thanks. In seeing what you stated, what I need is to have the cutter to be .890, with a 55 degree chamfer, and chamber pilot size of .811 +/-. The .811 size I didn't mike yet, but it would have to be chamber-.0005-.001 to keep it straight and I would guess made out of brass to minimize scratches.
That means the final size has to be turned with the pilot locked into the tool and turned to final size to keep it concentric.
I wonder how concentric the rim is to the chamber, is this cut and then the chamber follows or a separate process.

I will try one more time to simplify this conversation. The $160 tool that Jim and I are recommending does not pilot in the chamber. Disregard the chamber dimension, the reamer takes care of that. This tool pilots in the bore. If your bore is larger than .729, apply fingernail polish to the pilot until it fits the bore. It is a hand driven tool, it doesn't have to have an absolutely perfect pilot. Apply polish until it is a good fit in the bore. Don't try to measure the rim depth, you will screw it up. Run the rim cutter in until your shells fit in the closed gun. I have no idea how to measure rim depth any other way. Once your shells fit, just don't cut any deeper. What could be simpler?

Bill, thanks for the clarification. Without seeing tool it is hard to visualize what it is. Brownell's website didn't have a picture of tool and was confusing to me on how it worked.
Again thanks to you and Jim..