They sell throaters, but are out of throater holders.
So I made a throater holder.
It is a piece of tubing that I bored out to 0.2495" with a tiny carbide boring bar.
Then I drilled and tapped the tube for a 4-40 set screw.
After throating, I can now chamber a 3.1" OAL 260 Rem dummy round instead of a 2.6" with 120 gr NBT.
This should give me an extra 200 fps.