Larry Willis Collet issue

[Pheroze]

I have a problem with the Larry Willis collet die and my 400 H&H. I think it’s because the reamer I had made for the 400 H&H is made to create a base diameter on the cartridge of .514 (I have a copy of the plans). I use the collet die on a 7mm Mag and 308 Norma Mag. But when I try to use it on the 400 H&H it jams. The base diameter of a 375 H&H is 0.513 and this small variance is the only thing I can figure could be the issue. The resized brass chamber’s fine in the rifle without using the collet. And the fire formed/resized 400 H&H case is 0.514. I am posting this for general interest but if anyone has any other ideas I am all ears.