Idea for a new pistol?

[bigfatdave]

MachIVshooter don't dash my hopes for a PMR15!

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Interesting. I've never seen WMR in person, so that is why I was asking.

OK, then a lot of the conceptual errors are explained.
So, if you haven't yet, FULL STOP on this idea and go read the articles on WikiPedia on .22wmr, .22lr, and their parent cartridges.

.22wmr specs:
Parent case .22 WRF
Bullet diameter .224 in (5.7 mm)
Neck diameter .242 in (6.1 mm)
Base diameter .242 in (6.1 mm)
Rim diameter .294 in (7.5 mm)
Rim thickness .050 in (1.3 mm)
Case length 1.055 in (26.8 mm)
Overall length 1.350 in (34.3 mm)

.22lr specs
Parent case .22 Long
Case type Rimmed, Straight
Bullet diameter .222 in (5.6 mm)
Neck diameter .226 in (5.7 mm)
Base diameter .226 in (5.7 mm)
Rim diameter .278 in (7.1 mm)
Rim thickness .043 in (1.1 mm)
Case length .613 in (15.6 mm)
Overall length 1.000 in (25.4 mm)

There's a LOT more to rimfire than just ".22 long rifle" and variants
http://en.wikipedia.org/wiki/List_of_rimfire_cartridges