Nevada Ed - I have been wondering the same thing but I was afraid to post the question!
I also had not thought about the recoil sprang
. I have a new CS9 barrel that I might try this with in my 6906 ... once you report back! Using it in a spare barrel lets me get the 6906 back into action quickly should I stick a bullet in the barrel. Total SWAG: the pressure won't be too high as long as you don't compress the load, and I think it'll have enough pressure to obturate the case. Maybe one of the newer coated bullets will be slippery enough.