Most modern in-lines will safely shoot 150gr. This is not to say that's what you should
shoot. Most of the "big shooters" agree, a 28 inch barrel will only burn
about 120gr. of powder. If you like pellets, T7 makes Magnum pellets in 60gr. Drop 2 down the barrel and you're good to go.
I store mine in their original container and keep that in a waterproof military ammo box. Never had any problems using them a year later.
Keep yer powder dry!