Re: .410 brass shells: make your own!
Something I've thought about, but haven't tried. A syringe. Suck up a syringe-full and close the jar back. When you go to seal your shell, just squirt some down into it. If you keep the level all the way up to the spout, only that part could gel. The rest, inside the syringe, should stay liquid. Maybe.
Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297
I always take precautions.
Beware the Evil Bullet Fairies.