Nice, but not quite ArmaLite!
I think this is a great receiver for the price, but if you're considering an order, knowing a few things up front may be worthwhile!  This upper requires a DPMS-pattern barrel nut (threaded 16 TPI), NOT an ArmaLIte 18TPI barrel nut, as mentioned in the description. Neither one of my ArmaLite 18 TPI barrel nuts would fit, so I brought the upper in to my gunsmith, who measured the threads at 16 TPI. I then ordered a DPMS-pattern barrel nut (16 TPI), which arrived today, and threads right on. That may be good news for many buyers, because DPMS-pattern free float forends may be easier to find. It was bad news for me, because the 18 TPI ArmaLite forend I already own & had planned to use DOES NOT FIT.  This upper will hopefully work with my AR10B lower, but required fitting. The lug for the take-down pin at the rear of this upper receiver is just under a half inch wide, EXCEPT for a small 'step' where it meets the main body of the upper. That step is only about 1/8" high, and adds only about 0.025" to the width of the lug (~0.012" on each side), but it prevented the upper from closing completely on my AR10B lower. I carefully removed the step (both sides) using small hand files; the upper now closes completely, and both pivot & take-down pins lock in place. I think the upper receiver looks good on my AR10B lower, but the contours do not match exactly at the rear of the upper receiver, or on the left side (for a short distance forward of the bolt catch). Again, that doesn't bother me, but may be important to others.  This upper receiver is described as Type B, and Gorilla Machining politely confirmed compatibility with the AR10B via email, before I placed my order. However, this upper does NOT have the stops present on an AR10B factory upper receiver, which prevent over-insertion of the M14-based AR10B mags (and which may also prevent use of an AR10B upper on an AR10A lower). My AR10B mags lock in place with the upper receiver attached to my lower, and look like they should feed/function as intended - perhaps someone who owns both types of ArmaLite AR10 lowers may be able to tell you if the lack of stops allows this upper to also work on an AR10A lower. Anyway, thanks Gorilla Machining for a very nice upper, at an affordable price!
Reviewed by: Scott S. from Arizona on 8/20/2020