by SCJ429 » 15 Jul 2019, 6:21 pm
I have never used N550 but if it were me I would do a ladder test starting at 39 grains, then 39.5, 40, 40.5, 41, 41.3, 41.6, 41.8, 42, 42.2. You could try going further if you don't see any pressure signs however your short barrel may stop you getting much more velocity. If you have a chronograph, let it tell you if you are gaining meaningful velocity.
If you are not comfortable starting at 39 grains then drop another grain or where ever your comfort level is.
Why is your barrel so short, did it get cut or is it factory?