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.jpg

10.5 inch 450 BM on an ARplatform.  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!