For a bullet that intrudes so much into the cartridge case thus using up the volume that could be used for propellant, a big case is required. So the biggest reasonable case available is the 50BMG that has to be necked down to .375. This has been done before by David White in his BOOMER series. No drawings could be found, however. (https://www.shootersforum.com/wildcat-cartridges/13998-50-bmg-jdj-wildcats.html)
Apparently, Steve “Gunny” Schank has also made one however not with the obvious intention of maximising the volume.
So I drew a 50BMG necked down to 375 using those beautiful Weatherby curves for easy feeding. However, on second thought, I should make it harder to feed to give the barrel time to cool off. In David White’s words verbatim “for one, I do NOT chamber for these particular rounds in a barrel less than 30” in length! To me, it just doesn’t make sense and for the most part, most guys will go with a 34″ or 36″ barrel to help the cartridge achieve its full potential…
The velocity of these cartridges will run a good 400-500 fps. faster than what the Ultra Mags will and for the most part, 3-shot groups will run a consistent 3/4″ or less at 300 yards when fired from a bench. I tell the guys NOT to shoot more than three rounds at a time and then let the barrel completely cool down before it is fired again. Barrel “accuracy” seems to hold well for up to 1,000 rounds and with the barrel being as long as it is, after 1,000 rounds have been fired through it, you can shorten it 3″ and rechamber it and gain another 500 accurate rounds through it. By accurate, I mean being able to keep 3-shots inside an inch at 300 yards.”
However the volume of the .50 is maximised I doubt it will get the pseudo Sears-Haack bullet to more than 610m/s. However, that will be enough to study the supersonic behaviour of the bullet. Would LOVE to see that radar data.
Here is a rendering of the cartridge while I redesign the cartridge case:
That’s all for now