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AR-15 Match Builds I am starting my first venture into building a match grade AR-15 and have been reading the articles by Joe Carlos. I compete in Black Powder Cartridge Rifle and Black Powder Competition Rifle venues with buffalo era single shots, almost exclusively with Marlin Ballards, casting bullets and reloading for about 12 "hyphenated calibers" such as 45-70 Government and the like. This AR-15 project was a big diversion for me!

I was brought up on the M14 in the Marine Corps and carried an M16 as an infantry platoon leader. Of course, I had to buy an M1A once I retired from the service but never had a burn for the AR-15 until various factions started trying to legislate it away. However, I have long wanted a AR-10 chambered in 308 Winchester/7.62 NATO. This was my first foray here for me at age 65 and I have to say it’s an avenue I find very engaging, despite my late entry.

Aero Precision offers their M5E1 Enhanced Upper Receiver (AeroPrecisionUSA.com/m5e1enhanced-upper-receiver, as well as their M5 base model which has the more typical receiver extension. Being new to this I was attracted to the "integral free-float fixture" but after going on a parts buying spree and educating myself a little every day I see some drawbacks. The first was their proprietary hand guard.

I’m determined to proceed with what I have but I now see some issues such as your instructions in finding the sweet-spot with the barrel nut being problematic. Also, since the barrel nut on the Aero Precision is transformed from a female thread into a male threaded affair, lapping and bedding will be accomplished somewhat differently.

For the M5E1 the bedding will now have to be done between the inside of the barrel nut and barrel extension as opposed to the inside of the receiver extension and the and barrel extension of the simpler and more typical M5 upper. An overview video I found online discusses this: youtu.be/gb We ZI6gpis For my particular set up I purchased a Criterion barrel and the fit is fairly tight so right now trying to determine if bedding is necessary and if so, what best to use.

Squaring up the fit for the M5E1 is also a little different. G&G sells a tool which reaches down inside the integral free-float fixture and facing is done at the face of the receiver instead of on the face of the receiver extension. AERO claims it is not necessary but I’m inclined to use some 220 grit lapping compound and visually inspect the surface to ensure that is not just marketing talk. Thanks for the articles. I look forward to more in the future! Joe Carlos responds.

Thanks for the link for the Aero product you purchased. As it turns out I have built one rifle on this platform. It was an AR-15 in 224 Valkyrie. The customer supplied this strange upper and when I first saw it I wasn’t at all happy! Many car garages won’t allow customers to supply parts and a fair number of gunsmiths follow the same policy. I have been tempted many times to follow suit but I try to be as "user friendly" as possible.

On the customer’s receiver I measured the inside diameter and matched a custom BAT Machine extension to perfectly match the receiver. When I assembled the barrel to the receiver I applied green Loctite to both and had to tap the back of the receiver onto the barrel for about the last half of its travel. That is a perfect fit! Since you already have a barrel with a garden variety extension that permits slop in the fit you will have to proceed differently.

You might want to consider the custom oversize extension on future builds, however. I was able to tune harmonics on that build by varying the torque on what serves as a barrel nut. The gun doesn’t care what the barrel nut looks like or whether it has normal threads or something modified. The raised portion of the barrel extension goes to the rear until its travel is stopped by butting against the front of the receiver.

The amount of rear torque on the nut compresses things to varying degrees depending on how much torque is applied to the nut. So I was able to tune and you should be able to do likewise. John Madden Regarding fitting your barrel extension to the receiver, I have since improved this process. When using shim stock you absolutely must keep it from shifting position and ending up with part of it getting between the raised portion of the extension and the front face of the receiver.

Mess that up and you’ll create a high spot and the barrel will pivot around that during harmonic whip. This will cause the barrel to return to a different position each time it is

fired. Not good! Shim stock is shim stock so no need to be particular. I use 0.001" thickness but 0.002" thick shim stock will just need a section half as long as what I use to work. Here is the improvement: Degrease the inside of the receiver and the outside of the barrel extension. Cut your shim stock so it is more narrow in width than the extension. I want about 1/8" of clearance between the extension on the feed ramp side and again on the side facing the raised portion.

Apply green Loctite #638 to the face of the shim stock that is going to rest on the extension. Also apply Loctite to the extension in the area where the shim is going to be placed. I place my shims on the bottom of the extension 180 degrees from the locator pin that is on top. Wrap the shim around the extension allowing the 1/8" gaps in the areas described. Then quickly wrap a heavy rubber band around everything, tightly trapping the shim in place and ironing out any high spots.

Wipe off any excess Loctite that seeps out. Let that sit for a good 24 hours and then remove the rubber band and scrape off any excess Loctite that may have dried in place. Assuming that everything is properly in place and glued down you are ready for assembly of the barrel to the receiver. Coat the outside of the barrel extension and shim with Loctite and put more Loctite on the inside surface of the receiver. During assembly keep an eye on the shim.

It should not shift position if you performed the previous step properly!. Wipe off any excess Loctite and put the barrel nut on hard. I use a cheater on my wrench to get this really tight at this point. When you are ready to tune harmonics, break the barrel nut loose and apply your starting torque. Unfortunately, I have not found a way to true the front face of the receiver where the raised part of the extension butts against. That sucks because it is very important.

Aero is very wrong about the importance of getting that squared off! When I conducted my study of this I measured two brands of receivers: Aero and Rock River. While both were out of square, the Aero was worse! What can you expect for a lousy $100? I would be extremely careful about hand tools designed to square receiver fronts. During my study I tried one hand held squaring gizmo that fits in a 3/8" hand drill and using it made the receiver worse!

Without knowing more about the device you plan to use, I’d be very cautious. My study of 40 different receivers revealed that the proper receiver squaring procedure is to use a lathe, resulting in an average reduction in group size of 14%. However, I just don’t see any way to do it on one of these Aero receivers.

There are tons of AR outfits out there now and in order to distinguish themselves many of them come out with modification on top of modification to Stoner’s basic design but some of these modifications make things worse. I sincerely hope that nobody ever asks me to use one of these modified Aero receivers again! I would avoid that facing tool kit. The facing tool that I tested looked like the one in the set you are buying but it was regular AR-15 specific.

You already know it didn’t work and I seriously doubt that any of the fixtures you described will work either. What I think is wrong with these gizmos is all of them have to have a certain amount of clearance and nobody is able to keep that tool running perfectly straight. All of us apply pressure to the drill more left than right or more up than down or vice versa. The result is that using these gizmos result in one side ending up higher than the opposite side.

The maker of that tool set is like the maker of the receiver. Both will tell you that using their stuff will result in greater precision but may be making clever claims that don’t hold up. The video you shared stated that the front of the receiver "looked better" after using the fixture. We don’t make gun building decisions based on looks, we make decisions based on measured results and proper testing methods using the right test equipment and methods. AG