Common calibers (.30-06, 270 Win.) 2 to 3 years. Less common chamberings such as Hornet and Roberts 4 to 5 years. Rare configurations (carbines) and chamberings 300 Sav., .250-3000 Sav. 7 M/M and 35 Rem., 10 years+.
Not so much as just grabbing a barrel out of bin, but sales/popularity of a particular chambering related. Some barrels sat around for a long time.
