Bill,
I believe it is Harten but I could be wrong. It is essentially a regular crimp with a hole in the front of the loaded shell. Read further.
If you want a 2-1/2" shell, you cut 1/4" off standard 2-3/4" shells. There have been threads in the past how to do it. It is very easy to do. The STS shells cut like butter.
The important thing to know, which took me a long time to figure out, is that a shell length is the length after it has been fired not the length before it has been fired.
When you load a 2 1/2" hull you do not change the settings on your loader. The problem is the petals formed do not fully close the front of the shell and the shot will fall out. There will be a quarter inch round hole in the front of your loaded shell. You put an overshot card over the shot before you begin to crimp so that when the crimp is closed it will hold the shot in. It works very well. Sometimes you get confetti coming out the front of your gun when it is fired like you might with a roll crimp shell.
The overshot card can be bought from ballistic specialties or if you have lots of time you can make your own. A 12g. shell usually needs a 20g. overshot card or you will find it impossible to get it into the hull while you are loading.
I hope this makes sense.
