I've had awesome luck with prefits on my Nucleus. I've had one from PVA and one for Straight Jacket Armory. Both were great shooters. BTW, I prefer shouldered prefit over savage small shank due to getting a larger diameter barrel with shouldered.
I have 3 good random mausingfield barrels screw on and headspace fine on my nuke, but I did also have issues with one barrel from PVa being slightly short chambered and they offered to fix it. So sometimes shit happens.