Ah! Yeah, that makes sense, due to rifling twist rates.
300 A-Frames (and Break-Away Solids) also shoot very well in my Mark X .375 H&H. In fact it shoots well with almost any bullet, and also tends to shoot various bullet weights to the same point of impact, handy for field-testing. Which is why it's the only .375 I've kept over the years
My Ruger No. 1 .375 H&H, which I used even more in Africa, would shoot most 300-grain bullets to the same POI, but other bullet weights landed in various places. I did manage to work up a practice/deer load with 220 Hornady flat-noses at around .38-55 velocity that landed in the same place as full-power 300-grain loads. Used them considerably when practicing for an an all iron-sight safari 15 years ago, and the Hornadys exploded prairie dogs just as well as a .22-250.
