I mounted my Magpul MBUS directly to my railed gas block
This is a big NO NO . The gas block gets pretty hot cus the gases going through it . If you mount it to your hand guard / quad rail you should not have a problem .
I'm running my own test on this issue . I have not put enough rounds through it yet . still holding zero and has not melted after 300 rounds . 200 one trip 100 the next trip . Im not a high rate of fire guy so it's not likely to be a problem for me .
I do have a big BLM land shooting trip planned soon . Most likely will put 600 + rounds through it that day with some rapid fire . That will be the big test . I'll post what happens after .