….On AR platform builds


I have not been all that active here in the past few months or so. I had three auto racing series that I was heavily involved in trying to win, and I started building custom AR rifles in between races, and got carried away.
This past season has been strictly for me.
My first rifle build was a .300 BLK. 16″ barrel, Magpul OD furniture and the receivers skinned with tiger stripe wrap. I bought the complete DPMS upper for this on sale at a good price and originally had it on my 70s era SP1 lower. It was such fun to shoot I decided to make a dedicated lower for it.
I went online and bought two 80% lowers. from Hellfire Armory, but shopped the tool and Jig kit from DWP. Of all the different jigs out there theirs was the most professional and fool proof with a step by step video on you-tube to help get you through things. My friends would also want to use this.
I bought a heavy duty craftsman machining vice on eBay and picked up a collection of C-clamps. I familiarized myself with my drill press, set up some good lighting and reviewed DWPs video a couple times, making some notes on depth and tool speed to post near the press. I had other projects going on so I only did one step a day spending about 4 hours total over four days.
The  80% process
Federal law will allow you to build a rifle for your own use. It may not be sold or transferred even to a family member. If you are not familiar with this please see the BATF website for clarification. An 80% receiver is one in which only 80% of the machining/drilling has been done. In the case of an AR lower, the fire control pocket, rear takedown lug pocket, hammer and trigger pin holes and the safety holes as well as the trigger slot have not been completed. You must personally complete all of this work to remain legal. Another party cannot do this work for you. They would become an unlicensed manufacturer.
I assembled the side plate jig on the lower and drilled out both sides of the safety, hammer and trigger pin holes, then set it up for top plate #1 for the next day.
Plate #1 first spots, then drills most of the material out with a 1/8″dia. hole matrix, the trigger pocket at 1.22″ deep. and the rear takedown lug pocket at 0.60″ deep. Then a portion of these holes are re-drilled with 3/8″ dia. and 1/2″ dia. bits, removing about 90% of the material and making things easy for the end mill.
Another day and plate #2 is mounted as the guide for the 3/8″ end mill to finish the trigger pocket. I had to get a friend for these last two steps to lower the drill press handle by 1/8″ increments while I guided the lower, mounted in the jig clamped in the vise. The trigger pocket is almost finished.
Last day, plate #3 is the guide for the lug pocket and trigger slot through the bottom of the receiver. Also finished with the 3/8″ end mill, and H size drill and smaller end mill for the trigger slot. The friend again fed the drill press arm as I guided the work piece.
I chose to dehorn the raw finished lower, filing and finish sanding all of the sharp edges off. Most of the corners were only broken and looked pretty blocky.
I tried a couple of different finishes, all of which I disliked and stripped off the same day. I finally “skinned” the upper and lower with a hair dryer and Tiger stripe wrap. Looks good.
Other builds
This began an obsession with shooting and building AR platform rifles and figuring out the set-up template for our tactical rifles. What custom parts did nothing and which ones actually helped get you through a tactical course.
I started to collect the parts to build one of my buddies an AR pistol and also planned the most outrageous rifle that I could imagine.
The pistol went together in short order on a standard virgin lower we already had from a misplaced treasure trove of rare late 70s and 80s parts recently discovered in storage. The pistol uses a short tubular floating fore end, Vietnam era handle upper and front sight post/gas block on a 7.5″ barrel with Miculik comp. For legalities sake it has a plain black foam covered recoil buffer tube and no stock. It gave us a lot of laughs as it is so small, but shoots surprisingly well. 
What became the “Skull gun” was mocked up as a SBR with a 7.5″ barrel and a suppressor with a total barrel length of 16″. As I wanted to get this gun together without the long wait for BATF paperwork and the tax stamp and suppressor expense, that idea was temporarily ditched for a`16″ barrel covered with a dummy can, and a unique Strike Industries comp. It has a floating aluminum 4 rail fore end, collapsible battery and spares storage stock and MOE-K grip and sling points. The upper and lower were “skinned” with Black/grey skulls. It also received our tactical template of: B.A.D. lever, extended charging handle latch, SI ambi 30 degree safety and Magpul  ASAP & MS1 single point ring and bungee sling. Magpul Pro flip up iron sights and a Sightmark (EOTech clone) NV dot site and Lasermax IR laser. A CMMG .22LR conversion kit makes for cheap training. It is also set up to carry the AN/PVS NV or flip to side 3X magnifier behind the dot sight. This little gun shines through tactical assault courses, under cars, right or left handed barricades, urban prone, there is nothing it cannot master. As time and money allow, it may be changed to the original suppressed SBR idea.
A build to far?
During one of my online shopping ventures I found a LR308 upper for $64 and bought it with no real idea to build one, but it was cheap!
While putting together a light weight carbine upper for another friend I started shopping parts for two more friends future builds . I kept finding great sales on parts, and that LR308 upper was sitting there. I started buying for it also whenever I saw a good deal. I had just about all of the parts in the mail but the lower and the barrel. Did I want to build another carbine in a big caliber or something that could really reach out and touch you at 1000meters? I looked at many many barrels, a heavy fluted SS 24″ barrel 1 in 10″ twist from DMPS won out. When it arrived, and I saw the size of it, I felt like I was building an anti-tank rifle. The lower was also a decision. I was having good luck with 80% lowers. The LR308 was similar but very different and all together larger at the same time. It required a new jig but my old tooling would work out fine. All of my previous builds used Hellfire Armory lowers so I looked into their AR10 lower offering. They had a lower/jig package deal at a very good price, I ordered it.
The Hellfire package arrived with a very nice pre-anodized receiver….but the jig looked kind of cheap and not really suited to the process that I was use to. Just two top pocket plates with end mill guides only. No instructions, no video, only a one page cross sectional drawing with most of the dimensions for an AR10. I wasn’t too crazy about this jig. It may be sufficient for a machine shop, but not a drill press. I just couldn’t see my drill press hogging out all of that metal with only an end mill.
While looking over the jig and the drawing I noticed that the jig was wrong. The trigger group pocket has a tail that is to be offset to the left but the ONLY way the jig can be assembled is with the tail offset to the right. Big problem. I email Hellfire, after a week I hear nothing. I wonder how many people have destroyed their lowers with this jig?  Buyers beware, not all lowers or jigs are well made or compatible! Some careful measurement with a caliper and the plate flipped over and clamped fixes that set-up problem
Rather than search out and pay for another jig (many lowers and jigs are not compatible) I do a little creative planning and clamping using plate #1 from my AR15 jig from DWP and the guide plate from hellfire together. I use drill bits as locator pins in the corners to line them both up and clamp them.
The next week, working on this lower is a nightmare. My drill press cooks a belt, then the top plate of the jig moves out of alignment and I drill two small spot holes before I catch it, then the motor pulley loosens and looses the shaft key. Throughout all of this I am trying to drill out the metal and finally end mill the two pockets and trigger slot. I don’t have help to feed the drill press arm but discover that if I am careful, my friend can be replaced with duct tape. I finally have a good receiver. There are a couple of blemishes but they are not visible so the lower is assembled and functions properly including the forward assist and two stage trigger. The rifle buffer needs a bit of trimming for the bolt lock to operate.
I have had the upper assembled for fit only. I disassembled it and torqued the barrel and reassemble the fore end, gas block and pin the tube, mate the two receivers and check everything over. It is one bad assed looking long gun!




LR308 top, .223 Skull Gun bottom
The proof is in the shooting. More on that and my scope selection (either high end Horus reticle or old school Leatherwood ART camputer) later.
Regards, D.

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10 thoughts on “….On AR platform builds”

  1. Nope P.R. Just some assembly and guidance with them on their numbered receivers. I am strictly “hands off” on any 80%ers other than mine. I wont even do any machine set up. I do not create firearms for them, they must do all of that work. But I hear you. You need to read and follow Federal and state firearms laws carefully and follow their guidelines. If I did it all I’d be in trouble and they would learn nothing, and that is not my intent as a friend. I’m just a parts collector and instructor. Regards, D.

    • D. – you really have me wanting to make an 80% to 100%.

      Question though:

      If you cannot sell, give, or transfer an 80% lower once it is made 100% – How would anyone know? I mean – there really isn’t any traceability. If I bought a 100% lower from someone who completed an 80% – couldn’t I just say I bought it at a gun show and finished it myself?

      Any thoughts on this D. ?

  2. There is a mechanism called a “gun trust” that looks promising to legally pass on these receivers to your heirs. Google it.

  3. D, apologies, I had intended to respond to Rourke’s comment, “couldn’t I just say I bought it at a gun show and finished it myself?”



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