Hey Mineral Mega's are sweet ! Yep the upper and lowers are really well machined and do fit great ! Ive read where folks literally dunk the bcg in oil then sling it off.....me personally...I just give a new rifle a healthy dose of mobil one or Mpro 7 in/on the bcg....you dont wanna bake in oil or grease in the chamber,but I put just a tad of grease on the new bolt lugs and work the action a bit without ammo. Be sure and clean your barrel before break in.... I think the important thing is to lube up nice and good the proper ar lube points as described in an ar manual.... everyone has their " special " way of break in lubing...Yes ill run mine wet on the first out of the box break in,but oil running down my arm from the rifle...Nah ...dont forget to lube up the buffer spring ...I think that relubing your bcg is key after shooting a new rifle a while...like some folks say "If ya aint got oil spray on your shootin glasses then you aint wet enough" Wash