Actually, in the ones I have heard of, laws are just "no military calibers", where there exist. When the USPSA decided
that "Major 9" was just blowing up too many guns, getting ridiculous and outlawed 9mm Para being used for major
caliber, I commented to a USPSA BoD member at the time, "Well, OK, but somebody will just invent a
"new cartridge, the 9x20" and will make major caliber with that. Yep...they came up with the 9x23,
and some used the existing (IIRC) 9x21 which was used in certain countries in Europe (Italy, I think and
others) to get around the "no military calibers" law. So, my guess was a bit wrong, there was no 9x20, but
there was already a 9x21 that I was unaware of, and the USPSA folks did invent the 9x23 to make Major
caliber in 9mm handguns. Although, it most replaced existing .38 Super guns and were mostly built
on wide body 1911 platforms. Not sure how far the 9x21 went, I don't know anybody personally who
used it, but knew a few that used 9x23. Colt sold 9x23 bbl conversion units for a while.
Both the 9x23 and 9x21 were approximations of the .38 Super with rimless cases, but the 9x23
was loaded to higher pressures, I think.
I don't think there was a particular limit on power, just not using military ammo. I think this may be more
oriented towards insurrectionists using captured gov't ammo to fight the gov't than anything else.
en.wikipedia.org
en.wikipedia.org
And actually, in much of Europe the whole concept of armed self defense is nearly illegal,
and certainly carrying a gun for self defense is pretty universally illegal, no exceptions, as far
as I have been able to discern.
Huge restrictions, typically on never using "excessive force".....if you are attacked by a guy with
a knife, using your own knife or a baseball bat might be OK, but shooting him wouldn't be
legal....apparently not sporting.
Bill