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JBelk,
I have never seen or heard of a 40 with a 9mm head but anything is possible today.
I've been a revolver guy for the first 47 years of my shooting handguns. I bought a 9mm to compete in three gun and liked the way the CZ felt and shot that I bought another in 40 to see if it was good for daily carry.
I still carry my American Express (never leave home without it) pistol (357 Ruger 6") but I am wearing the 40 off and on around home to see if I can get used to drawing it and learn to shoot it into 2" groups like my 357.
 

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Much ado about nothing. All rimless cases have that tiny dimensional head-to-widest-body diameter difference. The reason I don't consider that to constitute a rebated rim cartridge (and I assume it is also the reason I've never heard of anybody in the industry using the term to refer to standard rimless cases as such) is the design purpose of a rebated rim cartridge is not being served by the tiny difference. That purpose is to adapt a case to a sub-body diameter bolt face. In the case of the 284 Winchester, for example, the design objective was to get more powder volume into a 308 Win-length cartridge. That meant fattening the case so it is 0.500" at the body diameter datum 0.2" forward of the head. The designers wanted to be able to use an unmodified 308 Win-size action, which is designed for a 0.473" rim diameter, with that 0.500" case body diameter, so they put the 0.0473" head on it. That avoided special tooling for a .308 action beyond using a different chamber reamer.

In the case of the 40 S&W, and other standard rimless case designs, the small 0.001" or so of excess body diameter does not surpass bolt face diameter or require special modification of the breech end of the gun to work with it. The reason is a bolt face's diameter is an extension of the chamber, which is already wide enough to accommodates the extra thousandth, as its taper changes with length analogous to the cartridge body taper. (I say "analogous" rather than "like" or "the same as" because some cartridges, like the 45 Auto, have a greater taper angle in the chamber than in the cartridge case.)

A side note: I have put in a call to SAAMI's attorney to learn if it is alright to post SAAMI drawings on a forum. Technically, it requires their permission and they have wording expressly forbidding such copying with their recoil energy estimation formula. As soon as I get through, I will know if we have to take those down. A link to the SAAMI standards is always OK.
 
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