I talked to one of the guys at accurate today and he told me everything should be GTG if I follow that chart. He said go with the 150 data as it is the closest in weight. He also mentioned that A1680 was very compatible and that they compacted it 125%?
So they are loading compressed powder charge at a maximum of 25% compressed is what I take it they are doing/saying, If this is correct, at 18.6g there is only .176 g of room left in the case, if Accurate is saying you can go over by 25%, I hope they are just saying that as a general statement about the powder, and not specifically to the 300 Blackout, that would put, for the blackout, at 23.2g, which would be a massive over pressure, guaranteed to blow your gun and you up.
So that being said, I am going to ASSume that they are just stating that you are safe to compress that particular powder to 25% and it will still perform as intended, as a general statement about the powder, and NOT specifically to the 300blk round.
Just ran the 19.5g with a 155g bullet (just changed the weight of the 147g M80 since there is no listing for the Palma), and yea, overpressure for sure-