Thus, "Have withstood pain to create many weapons."
I'm actually being serious in saying that.
Personally, I think that he's using them as temporary Magic Circuits. It's painful and damaging, but if he doesn't overdo it, he might be able to survive, even without Avalon.
Although, really, I think Avalon is the reason why both Shirou and Kiritsugu didn't have some permanent and crippling damage. IIRC, Kiritsugu had Avalon before giving it to Shirou in the aftermath of the Fourth Grail War.
On a related note, I recall reading that some powerful sorceror had written a revolutionary (and ingenious) thesis on a new way to harness magic power. This method was, IIRC, remarkably similar to the way Kiritsugu was supposed to have used maryoku, and was said to help overcome the decline of magic circuits in magic families.
Unfortunately, his master took one look at the completed thesis and tore it to shreds.
I wonder if there might be a copy of the thesis? I know I, for one, would never fail to keep multiple copies of crucial documents...