a/k/a “cut shells” or “ringed load” or “ringers”.
Apparently this was an old Depression era trick one could do in the field to convert a birdshot load into a slug. It’s easy to do outdoors with a pocket knife and has historically been used to poach deer during waterfowl season. When a shell is cut in this way the upper part of the hull keeps the wad and shot all together from the barrel to the target. The drawback, besides the safety issues, is that the you need to load these as a single shot. Also, waterfowl are generally hunted nowadays with steel shot. There’s plenty of skeet loads still on the market, though.

This is something I’m glad to know about, but not too eager to try. Still, I’ve highlighted this video by Iraqveteran8888 because it’s about the clearest demonstration I’ve seen from something I’ve only heard rumors and hearsay about.
The lost art of “Cut Shells” 3:53 min.
Click here to view the video in a pop-up window | Direct link
As a commenter stated over on the youtube page, “There ain’t no school like old school.”
Here’s another vid from the same source about improvised slugs made from shotshells. The improvised brenneke slug made with a drywall screw and a fishing sinker is cool, but I’m not sure I’d try it.
Lost Arts Part 2- Improvised Shotgun Slugs 4:23 min.
Click here to view the video in a pop-up window | Direct link
Here are a few more links I managed to search-fu up from around the web about “cut shells”. None of them are as good as the videos above though.
http://www.go2gbo.com/forums/index.php/topic,178695.30.html…
http://thehunterslife.com/forums/printthread.php?t=627
This last one is a copy of an article about cut shells in an NRA publication1. E. H. Harrison found that the practice actually reduced chamber pressure, but please note that the shells used were all paper hulled – none of which are on the market today. Nowadays our litigious society, not to mention backlash from advertisers, would make an updated version of this article impossible in mass-market media. Too bad, as I’d really like to see the results with modern barrel pressure measurements and various choke settings.
http://www.hunt101.com/data/500/003175.jpg
Be cautious with plastic shotgun shells. All the reloading manuals caution against working up your own recipes, unlike when reloading the metallics. I’ve always assumed that this is because the plastic hulls do not show the same signs of over-pressure like brass does. It would be easy to get into trouble, even using factory loaded shells, by say dumping out 3/4 ounce of lead shot and then gluing in a 1.25 oz. sinker.
I’d be remiss if I didn’t note the tremendous price difference between mass-marketed skeet loads and hunting slugs, but please don’t do this to save money. In fact, don’t do this.
1 Unknown issue month and year. If you know, please leave a comment.