You're not a sissy boy.
Whenever I fired the M14, BM-59, FAL, and HK-91, it always felt noticeably sharper behind the HK-91. Maybe because there's no counter-recoil from the oprod and heavy bolt carrier?
There's a page in the Shotgun News that advertises extended buttpads, among other things, for the HK G-3/HK-91. That would be one of the easy fixes. Muzzle brakes would have to be solidly affixed, and depending on whether the gun's pre or post ban, permanently modified.