425, I'd probably go lower than 8400 as well. Possible with a 16, but not as easy as it would be with a 12. The 16ga reloading group can come up with some recipes, I'm sure. I had Tom Armbrust test one load for me that came out right around 7,000 psi at 1150 fps, 7/8 oz shot, but that's unusually low pressure for the 16.