I'd recommend this product to others for their builds but not for my intended purpose - Spikes Tactical Billet Upper - Gen II - Mil-Spec Barrel Nut

I purchased this upper because of another review and having read elsewhere that the inside diameter for the barrel is undersized compared to mil spec requiring the use of a heat gun to fit the barrel. (similar to what JP calls thermofitting). Ideally I wanted a JP15 upper, but only the JP CTR02 upper ever seems available, and the CTR02 doesn't include basic features such as the ability to install a dust cover. Having read that this comes with an undersized ID for the barrel extension and required heat to fit the barrel I was expecting an upper similar to the JP15. I was disappointed to get this and find out that the ID is just plain old mil-spec. When I noticed my barrel fit right in with a little slop just like with other regular uppers, I checked it with my calipers, and sure enough, it measures right dead in the middle of the tolerance range for mil spec.