Very useful info on VERY high round count, extreme use ARs/M4s/piston uppers

[midnight rambler]

In excess of 100k rounds -

https://www.ar15.com/forums/AR-15/High-round-count-AR-M4-s-over-100-000-rounds-and-how-they-have-handled-on-our-range/118-677135/?page=1