The shelf life of smokeless powder is best described as " indefinite".....
If stored in proper container, in cool vs. warm/hot, and non moist location it will last over 40 years,,,,,,no doubt longer but .....have no experience in storing powder longer..........
Powder stored as a "loaded cartridge" ,in similar storage surroundings maybe even longer......
Have some .303 Cdn ball ammo from 1943.......still ignites well and gets its 2-2.5 in/ 100yds as of range session few weeks ago.........same can be said for some 1945 US 30/06 ball ammo likewise shot last month.....
hs4570..........your mileage may vary