AR 80% lower build

[ScrapMetal]

Finally received my spot drills and 5/32" reamers so I finished up my first lower yesterday. I had some "difficulties" setting up the lower in the vise and getting it properly situated. Putting a DTI on it after it was in the vise I was getting some odd variations front to back and top to bottom (it was on it's side so those terms are relative). After an hour or so of changing the way it was held, shimming, and other general messing around with it I decided that I didn't really know if the casting, especially after milling the pocket, was all that perfect in it's dimensions (and my "anal retentiveness" was getting in the way of actually making holes).

So I squared it up using the vise jaw as a reference and proceeded onward. I then spent an appreciable amount of time with a Blake co-ax indicator trying to find the center of a .251" hole. I don't have complete faith in the Blake and re-did it a number of times before I was satisfied with the results. First time I used it on a hole that small so I'm sure the more I use it the better it will go.

Being as things were not as "perfect" as I would like, and figuring this one would be a "test case" anyway, I ended up just spotting the near side, drilling straight through both sides, then followed that with the proper sized reamer. After I was finished I installed the trigger, hammer, and safety switch to test sizing and function. The holes came out within measurable tolerances and everything works as it should. The lower will now be dis-assembled until I receive my Brownell's order which contains a spray can of Aluma-Hyde II to coat the inner cavity and hopefully protect it from oxidation. I'd be curious to hear what others might be using for this.

Always waiting,

-Ron

[ScrapMetal]

Okay, you asked for pics, here are some pics... :biggrin:

The first couple of pics show how I set up the lower in my Kurt vise. I used a chunk of aluminum that was milled flat as a spacer/leveler to get the casting level side to side. The top of the casting was held against the fixed jaw in the Kurt which I had already squared up on the mill. I also placed a piece of cardboard to protect the trigger guard and magazine well edges.





No way would I try to mill anything like that but for making a few holes it was more than sufficient.

The next little procedure was to use my Blake co-ax indicator to establish the 0,0 mark for the DRO. Put the mill in back gear and reduced the speed to about 80 rpm.



Once that was established I simply lined things up for the hammer pin.


Installed a 1/8" spotting drill and marked the location.



Close-up of the "chips" from the spotting drill.



Followed that up by drilling a 1/8" hole all the way through both sides of the casting.



To finish out the first hole I used a 5/32" chucking reamer. Back gear and around 80 rpm again.



I'll spare you the procedure for the trigger pin as it was identical to the hammer pin.

Now it's on to the hole for the safety selector.



3/8" spotting drill doing it's thing.



In the next pic I used a 23/64" drill to make the hole through the casting. I could have maybe used a 3/8" but I don't trust the drills to be accurate and that would have left very little room for error. (Good shot of a long aluminum "rat tail". )



Like the previous holes I chucked up a reamer, 0.376" this time, and put the finishing cut on the hole. Here you can see where I had to slide the aluminum spacer out of the way. Once again, back gear and 80 rpm.



The "finished" lower.



A shot of the test fitting of both the hammer and trigger assemblies. I've since disassembled it as it's waiting for my Brownell's order and the Aluma-Hyde II paint. I did leave the magazine release and bolt release in as that shouldn't get in the way of painting the trigger/hammer cavity.



Now I'm just waiting for stuff to show up again. For this lower I'm waiting on a 7.62x39 upper from Northern Rifleman with a hand guard in Flat Dark Earth (the rest of the furniture will match). I'm planning on lowers for a .300 AAC Blackout, a 6.8mm Remington, a straight 5.56 x 54 NATO carbine w/piston, a 5.7 x 28mm FN (maybe, 'cause it looks kind of fun), and the more I look at/research it (thanks to Lucky 13 :p :biggrin: ) most likely a .223 Wylde.

Still just waiting,

-Ron

[ScrapMetal]

Tactical Machining was having a sale so I just had to pick up a few more. :biggrin: This time I picked up a few of the "raw" ones as I'd like to give Cerakote a try.

I did get a message from Brownell's that my Aluma-Hyde II is on the way. I'm a little concerned about applying the Aluma-Hyde as I've read that there could be issues with the spray nozzle clogging and that one should have extra nozzles on hand. Wish I knew that BEFORE placing the order. :p I'll certainly be posting to let you guys know how well it works out.

-Ron

[ScrapMetal]

Brownell's order showed up on my doorstep this afternoon so it looks like, with any luck, I'll be taping off and spraying some time tonight.

-Ron

[ScrapMetal]

Update on the lower.

Sorry it took so long, been kind of busy as of late. I did get the insides of the trigger/hammer cavities painted with the Aluma-Hyde but not quite as nicely as I'd hoped. The Aluma-Hyde II is great stuff and I love the finish (it matches the black oxide finish on the outside perfectly). My problem with getting a perfect coat were just "physical" issues with trying to spray paint the inside of a narrow, deep blind hole. The trigger area came out pretty good after the second coat but the take-down pin area was still a little "thin". The stuff sprays on pretty thick and I didn't want to try a third coat for fear of making it too thick in other areas.

FWIW - I think the next time I try using it I'll get the liquid version instead of the aerosol, use the thinning agent to get it to a better consistency, and spray it on using an airbrush.

Here is a finished lower waiting for the upper assembly to show up.



It'll end up being in a carbine configuration, 7.62x39, with Magpul furniture. I've got some fold-down tritium rear and front battle sights from Troy Industries to top it off. I'm also planning on some kind of optics but haven't quite decided on what, maybe Aimpoint...

-Ron

[ScrapMetal]

It occurred to me (I'm a little "slow" :p) that I didn't post the completion of the project. Here is the gun/lower in it's final form:



I finished it up with Troy Industries folding battle sights, front and rear (in the lower picture the eyepiece is moved to the side in order to raise the rear sight), an EoTech holographic sight and magnifier, and all Magpul furniture. The Troy battle sight is high enough so that it can be used without removing the EoTech sight though it might not look it from the pictures.



I have three 20-round and three 10-round of AR-Stoner magazines that I got from MidwayUSA. Five of the magazines perform perfectly. The sixth looks like it was from older stock (different follower) and the lip wasn't milled correctly so the rounds won't feed from it. I expect that once I file down the front lip that problem will be gone.

All in all it shoots great and is a really fun gun to shoot. So far I've got about a thousand rounds through it with nary a hiccup. This one's gonna be a keeper.

-Ron

[ScrapMetal]

I did not intend to come across as being opposed to jigs in general as I use them all the time, they have their place. Depending on your equipment and what you are trying to accomplish though, they could be more of a hindrance than a help. In the case of jigs for AR lowers all the jigs I have seen have been built/designed for use with a drill press or at best a mill without DRO or accurate measuring tools and have also been constructed out of aluminum.

Now, if all you intend for is to make a single lower, are not too concerned with accuracy, and don't mind some less than optimal aesthetics one of these jigs could possibly get the job done. It would take a load of patience, attention to detail, and most likely a number of "Uhhg crap! :concerned:" moments but it can result in something usable.

Here are what I see as problems with these jigs:

First of all, when the 80% lower is completely enclosed within the jig there is no way to tell if the lower's orientation within the jig is correct, "square", etc. If it's not then everything done from that point on can be skewed.

Next, when you use the drilling guides you will never have the drill perfectly in line with the holes. Even if by some miracle it was there would still be run out on the drill bit, drill chuck, or drill press table that would cause it to be "off". Granted, some of these issues apply to the mill as well so we try and minimize them the best we can. As the jig is made from the same material you are cutting (or even softer), each time you use that hole it will become more oblong and less accurate. Drill bushings would be great for the side holes (trigger group pins, safety, etc.) but if the drill is not started in straight there would still be enough slop to make a difference.

This also applies to when you trying to mill out the fire control cavity. You will need multiply passes with an end mill and each time you hit the side of the jig you will be taking a chunk out of it. Since we are not using a DRO to tell us when to "stop" all we can go on is visual and audio clues, both of which will result in buggering up the jig "guide" a little bit more each time.

Then there are problems in just using the jig. The drill/route guides covering the top of the fire control cavity created a couple of issues in itself. The first of which is that any drill or end mill had to be an extra half inch long to reach the bottom of the cavity so instead of needing a drill/end mill with a cutting depth of 2.5" you will need one with 3" of depth, a costlier tool with less rigidity.

I also found that the jig made it more difficult to clear out the chips as the "guide" acted like a lid over the cavity and kept everything right there making it more difficult to see what the cutter was doing and making the cut less clean.

Another issue was when reconfiguring the jig as every time you take it apart to put in a different guide there was no guarantee that once it was re-assembled that it would be "zero" with itself or the lowers orientation within it would be the same.

I could keep going but I've gotten across the general experience I had with a jig in this case. I am sure that there are some AR lower jigs that would perform better than the one I had in hand but even then some of these issues will just not go away. In my opinion, if you have access to a mill with an accurate DRO and practice proper cutting, measuring, and mounting techniques you would be better off without trying to use one of the lower jigs on the market.

JMHO

-Ron