My understanding is that proof charges now are 25% higher than the maximum pressure developed by any load available for the chamber length/pressure.

There are two kinds of prof - Standard and Superior.

Superior is for magnum loads, Standard for non-magnum.

So, a 12-bore 70mm Standard Nitro Proof will be for non magnum loads.

A 12-bore 70mm Superior Nitro Proof is for magnum loads.

For a 10 bore, rules will be equivalent.

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