Picked up some Sierra 210gr Match Kings!
 

I was at a gun show yesterday and picked up a bag of 210gr SMK's. I loaded up a few with 10.7grains of AA1680. I shot a couple to make sure they were cycling the action of my M1S 300 Fireball. Worked perfect with 1 ragged hole at 25 yards! I dragged out my Chrony to see what speed they were clocking - 785 fps! WOW!

Based on those results I would suggest a substantial bump in charge. Find 1100fps and work down from there, not a stuck bullet and up.

I should have said that I worked down to the 10.7 grains of 1680. I have actually gotten down to 10.3 grains now and everything still works perfectly. Maybe I should check the battery in the chronograph?

I haven't shot through the Chrony yet with the 10.3 grain loads yet.

Thanks for the input, everyone should be cautious when loading subsonic loads because the bullets can get stuck in the barrel. Be sure that the bullet actually leaves the barrel!!!!!!