Me too, this the largest/tallest MTM 50 round box you can get. My 338-416 Rigby Improved with my 323g CNC turned solid do not fit it. Have to carry them loose in a bag.
My 416 Rigby rounds fit it without drama and so did my 505 Gibbs rounds, it's only the VLD rounds that have trouble.
Although the 285gr VLD just fit in the H-50 XL in the 338-416 Rigby Improved.
The 505 runs 3.840-3.90 depending on bullet used and the 416 Rigby runs right on 3.750, both fit with ample room in the H-50 XL, but VLD bullets are too long at 4.20"
I really haven't found a box suitable other than custom CNC turned one's but they're just too expensive.
If anyone hears of anything suitable, let us all know.
Cheers.