...for the pistols/Safari were the same, pumping them more and more is a a waste of time as you found out, they were never power monsters with 10/11 fpe being tops but 7 is a little low, maybe look to re-set the barrel, the bolt handle should tighten as it's closed, if it doesn't then the barrel may have moved forward a bit losing the seal at the front of the cartridge.
A couple of protos were made using the Herald cartridge, they were a bit pokier