I have a 12 x20 insulated building out back, there is also my 1240 pound safe , my guns and all my reloading equipment, done it this way for years with no problems, I load
.357 Mag, 9MM, 38 special, .223 , .243, 30-06, .308, 6.5 Creedmoor, 300 Blackout , 25-45 Sharps
Have never had a problem