I got my 20ga FH 3.5" brass cases from RMC.
The case capacity in water is 234 gr.
It holds 215 gr of dense ball powder to the
base of 490gr 20ga hard lead slugs I have.
These cases use a 209Mag shotgun primer, and
I have mouth ID set up for .620 slugs as the slugs
and sabots I have are that size. These cases will
work good out to 35,000 psi, without extreme
expansion or resizing problems. Load of slow powder
will get 490 gr to 2500 plus at 25-27,000 psi,
6800 ft lbs, using the 30" barrel I'm getting to
put on the FBW Model L falling block.Ed