I'm going to say you should probably get about 140-160 shots of of the 13ci/3000 tank. That's if you don't waste a bunch at the chrony first. You could probably gain a bit by using a tight bore and running your velocity a bit on the low side......say 270ish.
This is based on the numbers others have posted here.
Etek 3LT grey/black f/s
Valken Proton greyish/black f/s
68 4500 PE stubby, LP output f/s
68 4500 AIR tank(no reg) f/s
Creed/demon eyes f/s