Just discovered that it is a snap to neck up the 356 Win case to .416 and hold it to COL 2.8 inches with Speer 350 grain bullets. The small rim is adequate for headspacing, and it will definitely cycle in a single stack magazine like the Jungle carbine.

Useful capacity is 49 grs of AA 1680, which should drive the 350 to 2270 fps. From an internal ballistics perspective, this is a BIG version of the 7.62X39. Same expansion ratios and range of velocities with much heavier bullets, but the same powders. 300 gr Hawks would do 2440 fps.

This round is more adaptable to bolt actions than the 416 JDJ, which is a single shot pistol round. The 356 case is extremely strong.

Does this already exist?

Sabot, I don't see where it would be much different,the JDJ is based on the 444marlin, would yours give you a tad more powder room?

The 416-356 is 0.225 inches shorter and has a slightly bigger case head and smaller rim....this should enhance feeding in bolt action rifles.