It's not an "urban legend", it's been common knowledge for years (actually, since the first Glock 17 hit the gun stores in the mid-1980's with "Jacketed Ammunition Only" written in bold print in the manual) and it's in the manuals for both brands. Glock couldn't stress it in strong enough terms when I took their armorer's course. Shooters who wish to shoot lead in their Glocks and H&K's for whatever reasons (usually reloaders and comp. shooters) simply buy "drop in" aftermarket barrels with standard rifling.