I just bought a box of Federal subsonic loads to try in my Belgian 1880's 2.5" damascus hammer gun. At 980fps +/-, pressure is likely in the 6k psi range, which is fine for my purposes. I also have a box of AA ultralights to try, so it will be interesting to see if there's any substantive difference. I've shot Rio subsonics a lot too, and they are great, especially at $5.69/box.

www.marklarsongunart.com
www.marklarsonart.com