Monday, January 20, 2014

Started work on 80% lower receivers

Finally got around to working on some 80% lower receivers.  In total, there were eight lower receivers waiting for me when I got home.  Four EP Armory lowers (pink, tan, black, and olive drab - all blemished discounts priced at $35), two Polymer80's which I did end up receiving after all (with one disposable jig, planned on doing the other by hand), one mystery reinforced polygonal lower bought off eBay, one HLF standard lower, and one old-style KT Ordnance lower, which was one of first 80% lowers on the market.  Not pictured are the two Jack Squat's AR15 flats.  They are a lot less than 80% so those don't really count, but I still think it's a neat idea.

Just as I suspected, all 80% lowers except the Polymer80s fit the CNC jig.  It's because of the reinforced siding above the axis pin holes that prevent the Polymer80 from fitting (I knew there was a conspiracy to force you to buy their specific jigs).  The only ones I had time to work on were one EP Lower and the mystery lower.  They both fit the jig perfectly.
The aluminum lower was a pain in the ass.  I used the CNC Machinery jig on my cheap $40 Harbor Freight drill press.  It was a lot harder than I thought it would be.  I used 1/8 drill bits to drill out the smaller holes, using machine oil to help keep things moving.  Then I used the larger drill bits, that was also easy.  The part where I started slowing down was milling out the extra crap between the drill bit holes.  After using a combination of dremel carbide bits and the provided milling bit I was finally able to mill out the FCG pocket.

Good enough for Century Arms
I did the whole thing by hand and it sucked.  A bunch of times the jig would shake violently and felt like it was gonna fly out.  Even if I carefully let the mill bit down into the jig it would start chattering heavily.  I've been told that use of a XY cross slide drill press vice would allow for more precision and stabilization.

Good enough for me!
That's probably the last aluminum one I'll do in a while, unless there's some new crazy Obama law that goes into effect and I need to create a bunch of ARs to help Governor Perry secede Texas from the Union.  The EPLower was a lot more easier to mill out.  I basically used the same method above and when you mill through the colored filler material you stop drilling.  At that point you can just use the milling bit with the jig and smooth out the inner walls.  After that you turn the jig on the side and drill out the axis pins with drill bits.

They both came out okay as long as you don't take it apart and peak inside.  Still not convinced the polymer will be able to handle .223.  I didn't assemble them or test fire them but I did drop in the FCG and an A1 upper and did a function check and it seemed like it should work.  The EP Lowers seemed to be a little too tight on certain magazines and do not drop free.  I didn't bother drilling the safety.  Colonel Samuel Colt didn't need safeties on His weapons and neither do I.  Plus I think by not milling out that area it gives a little bit of extra strength.

The KT Ordnance receiver is neat.  I think I read somewhere that back in the day the ATF said it was okay to have 80% with the pocket already milled out as long as the axis holes remain undrilled, but then they changed their mind sometime later (funny that they have a history of doing this, ie Len Savage, Akins Accelerator, etc).  The catch here is that the buffer tube trunnion is not threaded and the takedown pin holes aren’t drilled so there’s no way to align it to the jig.  I suppose you could align the bolt catch slot with the slot on the jig.  As for the buffer trunnion, I find it difficult to thread holes using just a T-handle, so this will be a project for buffer-less build.

The Polymer 80 was interesting.  It seemed to be made of higher quality material than the EP Lower and have really nicer magwells than the EP Lowers.  The jig came with all the drill bits and mill ends.  The jig is supposed to be used only once and then thrown away.  I clamped the plastic jig around the lower and proceeded to drive in the screws.  The metal screws met some resistance and two of the heads broke off.  I don't know if that was intentional - was that some kind of precaution so that the builder wouldn't try to re-use the jig?  I'm telling you those bastards want to nickel and dime you for their stupid jig!

Well I used the drill bits, drilled to the proper depth and then got to the point where you are supposed to chop off the top jig and use the end mill.  I really didn’t feel like taking a dremel cutoff wheel and trying to cut through plastic.  It seemed like if it weren't for those broken screws I could have taken apart the jig and re-used it to drill out the other Polymer 80.  I think I can still pull it off by having the plastic jig held together with C-clamps.  That's probably another reason why I quit working on it.  I have enough AR15 lowers anyways so I'll save these for later.


  1. I want the pink one! #dirtygirlfitness

    1. like omg we have so much in common we're like soul sisters.

      add me to your google jerk circle!

    2. The only jerk circle I am familiar with is ookie cookie (my fav game lul) but I will try to add you.


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