"I know of no handgun manual
(maybe someone can show one) that says +P+ is okay to shoot in it."
The HK USP manual says +P and +P+ are compatible with the USP pistol but with the caveat that it will accelerate wear and reduce the service life of the pistol.
(see page 21)
"Remember, the people on the Internet are just like you - ignorant, delusional, and dangerous."