Lot's of talk on this topic, thought I'd pass along what has worked for me. 1. This is relevant for Dillon progressive re-loaders and probably the RCBS "Rock Chucker" family of machines. 2. The "Brads Warehouse" shaved tool head is what really makes this task a winner, invest in one. Trim dies » BradsWarehouse.com - Custom made 300 AAC Blackout Brass 3. I was not able to get one of the Brad's Warehouse Trim Dies (out of stock) so I called the fine folks at CH4D and they made me a Dillon Trim Die in 300 BLK. 4. To set up the Dillon 1200 carbide trimmer on your Dillon progressive re-loader, see below: a. Thread the trim die in your position of choice in the shaved tool head (on my XL650, this is position #4), until about 1/4 inch protrudes from the bottom of the tool head. From the bottom, thread on a Dillon lock nut. b. Run the piston to full top position, screw down the trim die, until it contacts the shell plate, back off 1/8 of a turn. c. Run the piston to the the full down position. Hold the trim die and screw the lock nut snug to the bottom of the tool head. Wrench this sucker in place, better yet, use Lock Tight. d. Place the Dillon 1200 lock nut on the upper threads of the trim die and run it down to the bottom. e. Screw the Dillon 1200 Motorized Trimmer onto the trim die, screw it all the way to the bottom, until the carbide blade hits the trim die, back it off 1/4 of a turn, then lock it in place with the lock nut. f. Attach the electrical connection. Hold the motor to counter the starting torque and start the motor, make sure it does not move. if so, torque the two nuts down again. 5. Lubricate a few pieces of .223 brass. 6. Run the first piece of brass up into the trim die THREE TIMES. a. Run the brass up slowly until it hits the rotating blade, then come back down 1/4 inch. Run the brass back up a little higher, then back down 1/4 inch. Run the brass one final time all the way to the top, then return the piston to the full down position and let the press index. 7. Check your new 300 BLK brass with your GO / NO GO gauge, should be picture perfect. The inside and outside of the neck will need to be chamfered when you are done. 8. If you have a Dillon Brass Feeder System, lubricate your brass and dump it in and turn it on. By running the brass up, 1/4 inch down, up, 1/4 inch down, and full up, each 1/4 inch down motion allows the motor to "catch up" and creates a small chamber for the brass shavings to be sucked away via your attached vacuum setup. Trust me, before I did this ONE, TWO, THREE brass trim method, I destroyed a perfectly good Dillon 1200 Carbide Brass Trimmer, an expensive mistake. Brass Vacuum: I am using the Dillon Factory Blue vacuum surround with clear PVC flexible tubing to a Home Depot five gallon bucket. I cut a hole in the top of the bucket for the Dillon vacuum surround, then a second hole that goes to the shop vacuum hose. Brass shavings (and there will be alot of them) end up in the bottom of the bucket, no mess, no muss, no vacuum bags full of sharp metal fragments. This ONE, TWO, THREE method works well, is fast and efficient. You really get to know which manufacturer makes hard brass! If you do get accumulated brass in the Dillon Factory Vacuum Gizmo, just remove it's two screws and blow out any residual compressed air and re-assemble. Remember also to keep the press blown free of brass shavings, there will be some. Good Luck!