Interesting about the quantities involved. I'd have expected more successful start pressure for the same reason that full loads of H110/296 work, but light loads can fizzle and leave a bullet stuck in the bore. But then, that's an old formula spherical powder and hard to light, relatively. Lil gun is newer and a lot of the newer sphericals have more advanced deterrent coatings that don't cause the ignition issues the older ones did. May account for the difference in behavior you saw.
Commercial wadcutters, being loaded flush with the case mouth, don't leave a lot of room in the case for powder. As a result, expansion as a multiple of the unfired powder space is rapid once the bullet starts moving, and in order to make gas fast enough to keep up with that and not be large enough to burst the small powder space, they use small quantities of very fast powders. So it's an example you already have of a small quantity of fast powder verses a larger quantity of slow powder in that same gun. Pretty much proves that it's going to be better when you switch. Here we use about 2.7 grains of Bullseye or 3.0 grains of 231 in most .38 Special full wadcutter loads seated flush with the case mouth. This is right in the range of pressure and burn rate of N320.
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