So when first researching this build, I found that there were several ways I could go.  I could of bought a complete gun for several thousand dollars.  I could of bought the already built upper and lower assemblies, but I would of still paid more than I wanted, and not had everything I wanted included in the build.

So I decided to piece it together.  Keep in mind, this isn't a typical AR15 build, where all the parts are generally the same, and will fit together with some ease.  With a .308 AR build you can go the AR-10, LR-308 or the SR-25 route.  Some similar parts, some different, but I found there were more parts availability for the AR-10/LR-308 than the SR-25, so thats the way I went.



I went with the Aero Precision M5 receiver set.  I chose it mainly because it looked good with the matching upper, it is billet, and is priced very well.

With all the positives with the Aero receiver set, there is one huge negative.  Parts compatibility.

With most .308 lowers, a lot of regular AR15 parts will fit, however there are some parts that are .308 specific, and with the Aero lower, there are parts that are Aero specific.  So I am documenting MY build, and MY experience to maybe help someone with assembling one of these.


AR15 Parts that will work-


Trigger pins

Grip, and associated hardware

Buffer Tube

Safety Assembly

Detents and springs

.308 Parts-


Buffer Spring

Mag catch 

Parts that are Aero Precision M5 Specific-

Takedown, and Pivot pins

Bolt catch


I made the mistake of ordering a 308 AR10 upgrade kit from Palmetto State Armory, nothing in there worked for the Aero lower, so it was a waste of 30 dollars.

So in short, if you are using the M5 lower receiver, use the parts from Aero Precision right off the bat, it will save you in the long run.


Here is a parts list for my 308 Lower.

Lower - Aero Precision M5

Trigger - Geissele SD-E

Stock - Magpul UBR stock

Grip - Magpul MOE+

Pins - Aero M5 pins

Bolt catch - Aero M5

Safety - Battle Arms

Mag catch - Aero M5 with Seekins button



Steven LaBarre


I purchased the Aero Precision M5 set. Had a problem with a CMC flat trigger drop in. The trigger came with .172 pins, but they don’t fit the lower. So I went back to check for .154 pins. Those .154 pins fell all the way through with no friction to the lower. I determined if I use small anti walking pins my trigger will have a wobble. I don’t know what to do. Any suggestions?

— Michael Toews