Thread: How to make a D-type reamer to chamber a barrel

I made a chamber reamer for .357 sig a couple of days ago, and have made a couple of other chamber reamers and several projectile reamers using this technique.

Gundoc has it right, except I tend to cut the reamer in half before hardening. Much easier to do it on the mill when soft than trying to grind when hard.
I mill them very slightly over half and then harden, Once hardened and tempered, I use a fine stone to bring it down to exactly half.
Once you have the thickness sorted, you can do the relief angles behind the cutting edge. Basically you want to use a fine stone to make a small flat (2mm wide) just behind the cutting edge, coming very close to the edge but not touching.
On the back edge that is not cutting, you want to stone the edge off and even round it over a little, I have found this helps to prevent tearing and galling.

The key to D Reamers is having them exactly in half. Im talking within 0.05mm or better if you can do it. Erring slightly thicker than half is better than being a little under.

If you make them correctly, they will hiss a little when cutting and produce chips so fine it looks like a paste.
Run them very slow with lots of good cutting oil and back out regularly to clear chips. They should require almost no pressure to cut, if they do need a lot of pressure to get them cutting, the reamer is likely not perfectly in half.

Those cartridges you mentioned should be pretty easy to make reamers for as they dont have much or any body taper and no bottleneck.

Needless to say, you will need a lathe to make these. Can be done without a mill, but its tricky.

I cant get any photos to upload at the mo, ill try to add some pics later.