Gun Reamer?

That's not a gun reamer.

Its not any form of "gun" reamer I am familiar with.

Probably the EBAY poster was just keyword spamming. Its against the TOS, but ultimately all EBAY cares about is their own pocket.

Usually a barrel chamber reamer is used in conjunction with a set of Go/NoGo gages. However, some match guns are adjusted a little tighter than that. I recall watching Mike Scheerz of Gila River Gunworks chambering on his lathe to match a gun to specific hand loaded cartridge specifications. Shoulder fit, head space etc... I wish I had studied what he was doing more and shot the breeze a little less back then.

There are reams used for preparing a shotgun barrel for internal threading to use interchangeable choke tubes. The ones I have seen do not look anything like the one in that picture.

A gun reamer is a type of long reamer, usually made for reaming valve guides and fluid passageways in aerospace and other applications. They're were once made like a gun drill, with a single lip, thus the "gun" designation. The term apparently is also applied to any reamer with long cutting edges; I don't recall, having not seen the term for decades.

It's just a long reamer. What everyone (including me) were thinking of at first is a chambering reamer for rifles. Or, possibly, a shotgun chamber reamer for reaming out old shotguns made for roll-crimped shells so they can handle star-crimped types.

For re-chambering rifles, I would think a piloted tool would be the = standard design; use of a piloted tool it is without a doubt the process = I would specify where consistant and reliable results are required = regardless of whether the tool was being used in a lathe, drill press or = even being spun by hand.

The tool pictured in the ebay ad however, would probably more accurately = be described as simply a flat bottom reamer.....in typical usage, where = size and location control are both critical, it is either run in a = bushing or else a short portion of the hole pre-bored to a very slightly = oversized diameter before the rotating reamer is inserted; the oversized = portion is later cut away entirely or is removed by chamfering the hole = opening.

Otherwise, the hole can be chamfered beforehand, but your actual results = will vary quite a bit depending on whether the reamer is stationary like = in a lathe tailstock; or rotating as in a drill press....also, depending = on accuracy of centerline alignment, runout, and so forth.....