You may be right. I used the method described above using a 00 buckshot. I lubed the shot with Hobo Oil and wiped the excess off before driving into the muzzle. I was surprised as to how easy it was to push out after it was about 4 inches down the barrel.

I performed this twice. The first time the shot came out distorted, so I tossed it and tried again.

I'll try it again and select a better looking, less distorted shot I've pulled from a 12 ga shell. I have the exact same micrometer pictured, and have standards I've check accuracy with.

May do a few other barrels too.