Not all AR15 parts are made the same and sometimes its hard to tell. A few years ago I purchased a smoking deal on an M4 carbine kit from BlackThorne. The kit contained everything you needed to build an AR15 with the exception of the stripped lower receiver. The lower is the only serialized part of the rifle so that part needs to be purchased through a Federal Firearms Licensee or FFL. The parts went together easily but the completed rifle failed to cycle. I checked everything and eventually saw smoke residue around the A2 front site. The front sight/gas block is where the gas gets diverted into the bolt for the rifle to cycle. There was an apparent gas leak and not enough gas was being redirected into the bolt for the gun to cycle. After removing the A2 front sight I noticed how poor the surface area inside the front sight was made. It was clear that there was no way to repair this gas block and it had to be replaced. The new gas block worked perfectly and the rifle cycled fine. I had heard mixed things about this company. So if you plan to purchase from them, you may want to consider that the lemon factor seems to be fairly high. It might be worth paying a little extra for another brand. I know I will.
Vulcan .50 Caliber Rifle Blows Up and Injures Shooter
BlackThorne & Vulcan are the same.