I’ve heard of this before. I heard someone refer to it as an “Alabama bear ball”. In my most humble of opinions, this is dangerous and completely inadvisable. Here is a snapshot of a 12-gauge shell and a 20-gauge shell sitting on the muzzles of a 12-gauge and 20-gauge shotgun, respectively.
Without looking on the interwebtron for figures, and simply using my cheap, plastic dial calipers, I measure the bore size of the 20-gauge at .62-inch at the muzzle as compared to the diameter of the 20-gauge hull at .68-inch around the plastic. Similarly, the 12-gauge bore measures .73-inch and the hull diameter measures .79-inch. So, the plastic hull is .06-inch bigger than the bore on each bore gauge. When you cut the plastic so that it travels down the bore loaded with lead, it has to compress past the forcing cone between the chamber and bore. I know that six hundredths of an inch is not a large number, but it’s not exactly insignificant either. For the same reason that we don’t load and fire 3-inch shells in a 2.75-inch chambered gun, firing cut shells subjects the gun to far more pressure than it is designed to endure. It just isn’t safe.
The gentleman doing the shooting in the above video comments that this was fairly common practice during the depression. Fortunately we are not in a depression, and ammo of various types is still relatively easy to come by. When sumdood on the interwebtron posts a YouTube video showing how handy his modded ammo can be, ask yourself how much a box of slugs really costs. Weigh the price difference between birdshot and slugs against the price and sentimental value of a gun, and possibly your own health and well-being. I know that slugs are a bit more expensive than birdshot, but they are cheap as compared to the risk of a catastrophic failure due to misusing guns and ammunition. Granted, I think that this is a perfectly valid tidbit to keep in the back of your mind in case of a TEOTWAWKI scenario, but it is entirely too risky a practice in a world where good ammo is available for a variety of applications at reasonable prices. If you simply want the pellets to stay together and hit harder at short distances, look at Federal’s Flitecontrol offerings. Please do stay safe and have fun!