I have tried cartridge inserts for several decades. I have them for rifles and shotguns. There are inserts to fire 20 gauge in a 12 gauge. Pistol cartridges in big game rifles and 22 rimfire in handguns. The shotgun x shotgun inserts work well enough at 25 yards to make them a viable emergency tool. When firing a 20 gauge in a 12 gauge the pattern at 25 yards is good enough for hunting. I have a rifled 22 rimfire x 12 gauge adaptor that shoots well enough to hit a 4 inch bullseye at 25 yards. However my handgun x shotgun adaptors are not rifled and at 20 yards about half the bullets were keyholing. Now a company is making rifled adaptors and I have not tried them yet. I have tried many handgun round x big game round with differing results.