I would suspect a deecrease in pressure...
I've got some Peters "Rustless" 12 ga. 3" magnum paper hull factory roll crimped my late uncle gave me they all looked to be in top condition. I took a few squirrel hunting years back they felt and sounded ok when I shot them...I just couldn't kill a squirrel with them.
When I came out of the woods that day I shot one level across a lake they petered out and fell in the lake at about 40 to 50 yards.
How long before we see a decrease in pressure ?
I suspect the shells I shot were atleaat 50 years old.
