I think the bad rap MG barrels get is from guys shooting custom cast "HardCast" bullets
they get them presized, and don't slug their bores, so end up with undersized slugs that can never bump up, no matter how you push them...
hardcast slugs are not needed and in fact can be detrimental to good shooting. The ONLY reason I have heard that makes sense for the existance of HC bullets is so they don't get banged up during shipping..... pretty stupid reason if you ask me.
as others have said, FIT is king! shoot the fattest bullet that can chamber. IF you do size your brass, DON'T use a spud for jacketed bullets... get one that is 0.001-0.002 under your bullet size (for a 30-30, the spud/expander button for a 0.311 bullet works great).
and use an alloy that is moderately soft.. WW/Pb at a 50/50 mix with just a bit of Sn to help with castability/fill out.
for hunting, a 60-70% meplat, or with a shallow HP is all you need.
go a bit heavy for caliber, and you'll be right along side factory jacketed loads.
IIRC, it was Petemi who stated, best size of bullet is one that "Just" slided into a fired case with a hint of resistance. Bell the case just a but to ensure no lead scraping.
no need to crimp in a single shot, unless you find them moving in your pockets.
and remember this, a fine thread bolt can take more torque than a course thread.... think about it, and when you understand that you'll know why a microgroove barrel can shoot just fine!