I would not pull the breechplug if you don't have any water leaking from the plug. So what if the last 1/2" is a bit wider? That is where the powder charge is going, and will be burning. If the length of the wide spot were longer, and you were going to shoot PRB loads in the gun, it might make a difference. But it won't if you are shooting shot loads. Just stick with light 16 gauge loads and enjoy shooting the old gun. And, use ONLY black powder. The Subs burn at higher temperatures and creat higher pressures. Not much higher, but when dealing with an antique gun, BE NICE! It will last a lot longer.
I am shooting a shotgun my grandfather owned that dates to the late 1890s, or early 1900s. It is a " Hardware store shotgun, made in Belgium, but marked with the hardware store's name. It has exposed hammers, and originally had full choke tubes in it. The family history says he used it to go duck hunting with his brothers and cousins in Michigan, but no one in Chicago remembers Pap bringing any ducks home! They all think the guys just drank, and played poker in the cabin, rather than go out in the cold blinds to shoot at ducks. My grandfather never talked to me about those days, or his shotgun. I inherited it after his death. I had to cut 8 inches off the barrels, because the right barrel had a deep long scratch or crack that ran that deep down from the muzzle, and right through the choke, in the very thin muzzles. Its now a cylinder bore DB shotgun, with exposed hammers, and the guys in the CAS sports always drool over it when I have it out at a range. With 22 inch barrels, I have used it to shoot dove, and pheasants hunted over pointers.I also do okay with the gun at Sporting Clays. I use only light 2 3/4 dram, 1 1/8, or 1oz, loads in the gun, to be nice to the old girl.
