The 'tons per sq inch' is quoted directly from the ammunition manufacturers' catalogues of the period. The only way to compare modern reloads with the originals is to use the same methodology (even the same equipment in Wrightie's case!).

No-one should really care what the actual pressure is, because that is totally irrelevant. What is critical is that the pressure is equal to or below the working pressure for which the gun was originally proved. Wright set out to deliberately demonstrate this with modern powders and loads. His book is still the best reference for that level of information by far.

There are 2,240 lbs in a ton. A 10-ton load is 22,400 psi.

Keep it simple.....