I never had any problem with high speed LRs in any of the 12-121 series Remington pumps and my 12S was chambered for the ".22 Remington Special" (aka .22 WRF) and fired a bucket of them without any damage. I couldn't tell any difference between its action and the regular 12A. The "Special" runs at a higher pressure than any of the LRs (except perhaps the ultra-velocity like Stingers--not sure about those).
The only common old pump .22 that I know of that has problems with high speed ammo is the Savage/Stevens series of hammerless guns. They don't seem to be dangerous with high speed ammo, but do wear out and stop functioning if you use a lot of it.
