180 gr nosler partition;
9 grains IMR 4227.
I'm running a 16" 1:7 barrel.

8 grains will not cycle the action and at 10... i hear a boom.

Your rifling twist is pretty tight compared to my rifle with a 1:10 twist. This can be a problem with chamber pressures as well.
Any load above 9.3 will be very close to the speed of sound, and with the tighter twist it is hard to calculate just what velocities are being developed.
I also use a good crimp to prevent the primer from blowing the bullet out of the case before normal pressures are reached.
you may have to go to a lighter recoil spring in order to get the rifle to cycle with your bullet/load.
My rifle's slower twist rate allows me to keep my bullets under the speed of sound and still have safe chamber pressures using more powder than 10 grains at my 8,000 foot altitude.
You may have to try a diff powder such as AA-9 or even Lit'l Gun to archive the velocities and action cycling you need.

For what it is worth, my experience with 4227 in a BOLT 300 whisper is that there is a very fine line between subsonic-supersonic and blown out primers. I used 240 gr. Sierra HPBT.
Eventually went to Lil'Gun and/or AA-9 for subsonic rounds and have not looked back.
I get consistent velocities with them.
Currently using 8.2 gr AA9 with a 250 gr. specialty bullet made for extreme expansion and it is quite effective on deer.
Sorry I cannot add anything related to cycling the action.

Gary