not sure about the inches on the arms, but you would need AMAZING genetics to add one lb per week of actual muscle w/out using gear. I think the avg is around one lb per month of muscle w/out gear. So a lb per week is possible, just not very likely.
Old school rule of thumb. To add 1" to your arms, you need to gain approx. 20lbs.of body weight. Best way is compound lifts, Bench, Squat, deadlifts, miltary presses, and bent-over-roll. The 5 holy grails.
2 inchs on your arms may be possible and obtainable ...
I don't know how you would measure " just the bicep ? "
The tricep makes up 2/3 of the arm so if you hit the tri's and bi's hard then 2 inchs
is possible although if your nailing them all the time then the pump never leaves which is a false measurement compared to a cold arm in the start ....
Guy's who want smokin guns should concentrate as much on the tri-cep as they are bicep work and you'll fill out that tee-shirt hole alot faster ...