I posted this as a question a couple days ago but have reached my own answer.
First caveat! Take this information and use it at YOUR OWN RISK!. I have been called a moron by a lot of people dumber than anyone here. Your Mileage may vary. Taxes, license plates and dealer prep are extra. Should you develop an erection lasting longer than four hours seek immediate medical attention.
First off my calculations.
https://i.imgur.com/UZotIxm.jpgI started by looking at the 454 Casull which I think somewhat close to the 450 BM as far as a pistol length barrel goes. From the top, determining gain in feet per second per grain of powder in this cartridges range. Change in velocity versus change in charge weight.
54.8 feet per second per grain of powder in THIS CARTRIDGES RANGE. I would have to lessen the load by 4.98 grains to go subsonic with the other things remaining the same.
Next I interpolate the relative energy between VV 3N37 (and not shown) VV3n38. 3n37 has about about 1.47 times the energy estimated IN THIS CARTRIDGE, IN THIS RANGE OF LOADING! So I need to scale down my load to 67.8% of the H4227 and Lil Gun. The last step is calculating how much VV 3N37 I need and I come up with. 13.9 Grains. I'm going to start with 13.3.
Second, Here's the setup.
https://i.imgur.com/HI8C2aq.jpg10.5 inch 450 BM on an AR platform. Magnetospeed Chrono on a Caldwell Sled. 50 yard target.
Chrono results; 3N37; 1010, 1071, ERROR. AVE = 1040.5. We're in the ball park.
3N38; 1000, ERROR,ERROR. AVE = 1000.
I have a screw loose. ...in my Magnetospeed!
Third, Results.
50 yards. Three feet of snow. Took half a dozen trips with the snow shoes on to pank down the snow so I could see the target burm.
https://i.imgur.com/NYIgugK.jpghttps://i.imgur.com/HMXxhHz.jpgSo there you have it. I went from 13.3 3N37 up to 13.8 3N38. Placed some white paper tablecloth stuff in front of the bench and saw no detectable un burnt powder. The action did not cycle and had to hand eject each case. I think (hope) the suppressor will add a little more back pressure. Running the lightest buffer I could find now. May try trimming some coils of the buffer spring or lighten the bolt carrier. Stay tuned for further revolting developments.