I like longer if the barrel will take it. 1911's, M&P's work with 1.135 or so. However my CZ SP-01 has to be shorter with some bullet designs ( MG 121gr). Try a round in your barrel before loading a bunch.
My favorite load at this time is Montana Gold 200gr JFP with 5.2 to 5.4 gr VV N320. My Les Baer and Wilson like 5.2 best and my Kimber Super Match likes 5.4. These loads have been the most accurate for me out of many I have tested.
I have two 550's one for large primers and one for small primers. It is very convenient. Usually one is set up for 9 mm and the other for 45 acp which I load a lot of both. If you can do two 550's it is really handy.
Has anyone tried the Storm Lake drop in barrel for the M&P Pro. Did it improve accuracy? If so, was it significant? Was it really a drop in fit? Thanks for any help. My Pro shoots good but I am allways looking to do better. LesM
My current favorite load for 45 single stack is Montana Gold 200 gr JFP with 5.2 to 5.4 grains of VV N320. I haven't chrono'ed it yet but it is very accurate.
I get cresent shapped brass slivers in the primer cup area if some 45 military brass with former crimped primers slips into my mix of brass. Best to avoid crimped primers or swage the pockets.