As a person who has done a quite a bit of pressure testing there is one thing I would like to point out. If a gun is limited to 100 or a 10 or 120 gr of loose powder then you are really pushing beyond that limit by shooting 150 gr of pellets.
Do you really need 150 gr of anything? The honest answer is certainly NOT; the very little you gain if any is matched by a large increase in pressure and recoil.
And an other point is if your gun is limited to 100 or there abouts it is questionable and risky to use 777 or Blackhorn with out reducing the load by about 20 percent especially with bullets over 300 gr.
Depending on barrel length ignition and type of powder used the peak of efficiency will be between 80 and 120 gr usually for 1-28 twist 28 inch barrels it is between 95 and 115. If you would like to figure this your self for your particular gun, bullet, powder combination the simple way of doing it is to Chronograph the loads on the powder ladder for at least 2 above and 2 below your load with 10 gr separation then figure the feet per second per grain for each load the most feet per second per grain is the most efficient load. This will not be the fastest load as you will gain in velocity as you increase the load up to the point where some of the powder does not burn while the bullet is in the barrel once you reach this point all that increases is the recoil.
Progressive powder is a different principle so this does not apply to Blackhorn or smokeless, if you increase the load with progressive powder the added pressure makes it burn faster so you can burn more powder there for a person must be doubly careful not to double charge or otherwise over load with them. Lee