Brian, I have loaded for my 20ga Flues with success. Finding loading data for a folded crimp 2 1/2” 20 gauge is difficult. I believe Ballistic products has data that you could purchase, but I haven’t went that route, so I don’t know what that data is like.
My approach has been to use 2 3/4” data in a hull trimmed down 2 1/2”. I use the Hartin crimp method. You use a 28ga overshot card and then crimp as normal. It creates something that is a cross between a folded crimp and roll crimp. No adjustment needed to the press if you are already loading 2 3/4” shells.
I used to load IMR 800x powder, but that has been discontinued. Now, I have switched to Winchester 572. If you look at the 572 data for Federal hulls you will find plenty of loads below 8500 psi and some in the 7000 psi range.
After you make some shells, send them to Tom Armbrust for testing, to confirm the pressure.
Hope that helps. Best of luck!
Tom Armbrust
Ballistic Research
1108 W. May Ave
McHenry, IL 60050-8918.
815.385.0037
E-mail - barbmiller49@yahoo.com
Last edited by DaveB; 11/07/21 10:46 AM.