In the 70's I used to get "new" rivets from Fullerton Air Parts. Picked them up on Thursday, as they were the freshest. Would drive well at 60 psi at the gun. Within 3 days, 80 psi and longer burst.
Then after talking to a "pro" I used the HT ovens at Fullerton Community College. Problem is, Temp control is very important for annealing. 10 degree window at around 925 deg. (from memory, check yours). I think if you exceed 938 you "kill" the rivet.
After annealing (only with clear anodized rivets) they'd drive at 40 lbs in 4 hits as I VERY CAREFULLY tickled the trigger. In 3 days, I was back to 80 psi with the long burst.
Reynolds Aluminum has a reference book. Consider taking the rivets to "W" temper (what most people call "annealing" by burning off Sharpie ink or soot).
Soft rivets stretch the skin the least and results in much better airfoils, etc.