The "why not?" is pressure. There is no good reason to horse a double, and 16 tons is already plenty.

Were I having a new .400 built, I'd have it regulated with current factory Kynoch. That way you'll be able to get good accuracy with factory ammo, rather than being stuck with handloads only. You might want that option sometime. The current Kynoch is good ammo, and it's easy to duplicate with handloads. The above load does so in my rifle. New ammo from Hornady will also be available soon.
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