DIY Upper- How Hard

[Slaxer07]

Pinzgauer,

Excellent response. Installing AR15 barrels is a breeze when you have the right tools. I can't think of too many other rifle platforms that allow the user to do barrel installation or part replacement like with the AR, which is one of the reasons why it's such a successful design.

You brought up the issue of barrel-to-upper receiver squareness. I understand how this works on bolt guns, and met a smith at a local range last year that does it on AR15 & AR10 builds. He said he made his own tools for checking and cutting the upper receiver extension face true, truing the threads, truing the barrel extension threads, truing the barrel extension flange on the rear and front, and truing the bolt carrier raceway. He also trued the barrel nut inner flange, and trued the lugs to the barrel extension. He was shooting sub-half MOA groups with his Grendel, so I can't say that he was doing anything wrong.

I just want to get into making sure my upper receiver extension face is square to the barrel extension flange, and that those are square to the bore axis. Aside from accuracy, I think these are important for reliability and bolt life, as imbalanced loads on the lugs will shear them quickly when the barrel is not square with the upper.

What are your suggestions for purchasing or making a tool that checks for upper receiver extension face squareness? I've been thinking about a tool that fits inside the upper raceway from the front, and can turn on the face of the extension. If you wanted to get really picky, you would true the inner flange of the barrel nut, so it will apply evenly-distributed compressive force against the barrel extension flange and the receiver extension face.

LRRPF52

AR Receiver lapping tool Brownell's has one also.