I have had no problems with my M1S upper they are "er shaw" barrels like all the other ar upper out there, I think you need to look at the reloading aspect first and foremost, the subsonics are a very finicky round to load, but once you find a sweet load all is good ,,,,,,,,,,till the temps changes,,, nah it aint that bad all the time but it is tricky, shoot one and you will love it
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