It is of course totally true the gun reacts to pressure, doesn't matter if from black or Smokeless. There is however a major difference in Black & Smokeless. A very simple little trial will show this difference dramatically. Scoop out about a teaspoon ful of each onto a dry hard non-flammable surface & light it with a "Long" match. The Black will go up with a "Whoosh", the smokeless will be hard to ignite at all & then just mostly smolder.
What does this prove, Black will burn at substantially the same rates regardless of other conditions. Smokeless on the other hand requires a certain amount of pressure for reliable burning. Many of these "Low Pressure" loads are skirting the ragged edges of their practicality.
To get loads which do not exceed that 6500 psi It is likely you will have to go with a lighter shot charge than the 1 oz which is more or less normal for the gauge. This may be acceptable for your purpose. On the + side with its smaller combustion chamber than a 12 the 16 "May" burn the powder a bit more efficiently at lower pressures as you will be using the same strength primer to ignite a smaller charge.
My "Own Personal Belief" as far as any of my guns go is "If" it does not seem capable of handling 8K psi it is either relegated for Black only or the wall.
