Receiver Lapping??

[customcutter]

DNS, there are ways to determine whether or not your upper needs to be trued. However, unless you're a machinist and already have the tools and know how to use them, they would cost more and take more time to set up and determine if your upper was square, than using the tool that you linked. There is no way that the tool can be made in-correctly if it was made on a lathe, unless it has an obvious nick or ding in it.

It is cheap insurance to insure the squareness of the barrel & extension to the upper, and therefore accuracy.

Here are a few more tips you might want to consider.

http://www.65grendel.com/forum/showthrea...rt-Whitley