Fixed: 18" Alexander Arms barrel: 2.5+ MOA

[LRRPF52]

Yeah...all this.

I sent it in, so no pix. The extension pin only flattened the threads on the barrel. The pin did not protrude any more or less than other barrel extension pins I've seen. It certainly did not interfere with the barrel nut being spun on.

There was NO drilling. The pin looked like it had been tapped into place and it flattened a few threads. It may have been pressed, or it may have been lightly hammered. Regardless, it obviously was not securing the extension to the barrel.

The torque value and assembly method of the barrel extension is enough to keep it in place if done to 120ft-lbs. The M4 Technical Data Package calls for the indexing pin to be installed with a press fit, no drilling into the threads.

Some AR15 barrel makers in the after-market choose to drill and pin into the barrel tennon threads, but this is nowhere in the TDP. There is no reason to rely on pinning into the threads if the extension is torqued on heavily.

We've seen problems with some manufacturers who drill and pin, where the chamber will expand into that thin area created by even shallow drilling into the barrel tennon, which is probably why the TDP doesn't call for it after extensive testing by the US Army Small Arms Research Lab.

If someone is telling you that it is standard or mandatory to drill and pin into the barrel tennon, they are simply incorrect.

If I remember right, we had this problem a few years back with some initial group buys with one of the vendors.

A few guys had brass coming out with this strange circle mark on the side of the cases. Looking inside the chambers, you could see a little circle indentation where the chamber pressure pushed the wall out in that area that had been drilled above with the indexing pin.

It can be done if the drill is really shallow, but isn't necessary or called for.