Somewhere in this forum I read a brief post by a gentleman who said he uncrimped the cheap Walmart 100 pack shotshells and replaced the shot with a Lee slug. I apologize, I can't find that post now. However, I was sitting in my loading room a few days ago looking at a can of Lee slugs and a box of the Federal 100 pack shotshells. I began to uncrimp them, place a base wad made from some thick corrugated cardboard I had nearby and then I simply re-crimped them on my Mec. I made up 10 of these and shot them yesterday. Recoil was not bad at all. My battery was dead in my chronograph so no velocity readings. Surprisingly, they fired 5 rounds into 5 inches at 50 yards using an ancient Remington 870 with an 18" barrel and a massive XS big dot front sight. The XS sight covered the upper area of the IDPA target I was shooting at. The load was about 8 inches below the center scoring ring, if you can quantify that given the sight I was using. It was great for windage. The fired shells did not seem to exhibit any symptoms of excess pressure and ejected just fine.
I also managed to hit the 16" gong at 100 yards 2 out of 5 rounds by sitting the big bead on top of the gong. I am going to explore this load more with a chronograph and maybe another shotgun with some better sighting equipment.
Anyone else tried this?