AR-15 Lower with Customer-Supplied Material


June 12, 2013, 11:02 AM
I routinely work with new aluminum alloys in the aerospace industry. So, just for fun, I'm considering getting a small piece of one or two such alloys for a unique build.

Does anyone know of an AR-15 lower manufacturer / machine shop that will make lowers from customer supplied material?

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June 12, 2013, 05:16 PM
There are a several issues... that I won't get into because that's not the focus of your question. I only know of one company (not saying that there aren't others) that has the capabilities to take a raw slab of an (possibly) unknown alloy and turn it into a lower, and that's Rainier Arms in Auburn, Washington (


June 13, 2013, 08:40 AM
Any of the literally hundreds of CNC shops that are cranking out 80% lowers could do it for you. You'll have to do a little final finishing yourself. I doubt that a real FFL would touch it.

Google "AR 80% lower" and contact any of the shops that pop up. I bought 4 of these for $105, shouldn't cost you too much if you can talk them into running your stock instead of theirs for one piece.

June 14, 2013, 04:43 PM
I just shot off a dozen or so emails to various shops seeing if they would be willing to make either a finished or 80% lower from my material - I'll update if anything ever comes of this.

June 15, 2013, 09:55 AM
I bought 4 of these for $105, shouldn't cost you too much if you can talk them into running your stock instead of theirs for one piece.
Have you actually received any lowers from Rockethub projects yet?

June 27, 2013, 10:55 PM
Its not difficult to do, if you are already set up to do it. That being said, most 07 FFLs that are set up to do it, are so busy making their own that it really wouldn't be worth it to for yours in, unless you were paying a mint to have it done.

Well heck, since Ranier does it, they must do it for everyone, huh? Have you looked at their page lately? The only ones as of 2 minutes ago on their page, as far a their house brand goes, are their forged lowers. Milling out a forging and milling out a billet are very different programs. And I'm not saying they do or don't, but the majority of 07 FFLs don't make their own stuff anyhow. They get another shop to do it on a variance.

July 8, 2013, 06:23 PM
I believe I received responses from all vendors contacted, but only one was willing to take this on. The remainder politely informed me that they do not perform this type of custom work. Custom Built Arms ( has offered to work with me to get my material turned into two 80% lowers. Initially I was hoping for a finished lower, but I'll take what I can get. Plus, a DIY project could be fun :D.

I'll document my experience from here out in case anyone else is interested in going this route in the future.

To start, the CB Arms requested blocks at least 1.75" x 4.0" x 8.5" to serve as a blank - I got mine as scrap pieces slightly larger in each direction just to ensure there was adequate material.

Next step - getting the material to the shop, of course. Boxed up and ready to go!

July 9, 2013, 10:48 AM
Hurrah! Good for you.

July 9, 2013, 01:42 PM
I'm definitely interested in this build, so please take pictures and update us often.

One question though: I am not a metallurgist so please don't get too technical, but do you feel that your alloy will be an improvement over the 7075 in some way, or are you more or less doing this "because you can"?

I'm all for doing things just because you can, and so I'm just curious as to your intention.

Good luck, and keep us updated.

July 10, 2013, 04:41 PM
I'm mainly doing this because I can. I just thought it would be nice to have a unique piece with a metallurgical "neat" factor.

From a performance perspective, it will be pretty comparable to a 7050-T7451 or 7075-T6 lower. As compared to the conventional alloys/tempers used (6061-T6, 7050-T74/T7451, 7075-T6, 7075-T73), there are some advantages with this alloy:

- Density is about 3-5% lower than the 7000 series alloys. Not much, but will cut the weight of an equivalent finished lower by about 0.3 oz.
- Toughness and yield strength are higher than that of the aforementioned alloys, but ultimate tensile strength is slightly lower than that for 7075-T6 and 7050-T7451.
- In the event the finish is ever worn or scratched, corrosion behavior is better than that of the 7000 series alloys.

July 29, 2013, 05:54 PM
Just a little update on where this project stands. The blocks went out to the production line at CB Arms two weeks ago (7/15), and I hope to have the lowers in about 2-4 weeks.

I'm also expecting a mini mill and a little bit of tooling to arrive over the next few days. Once I get everything set up, I'll use the time until the lowers arrive to familiarize myself with the equipment, make practice cuts, etc.

7.62 Solution
July 29, 2013, 07:53 PM
Very interesting project, I look forward to updates and seeing the finished firearm.

July 30, 2013, 02:53 PM
"...familiarize myself..." You have any machining background?
You going to tell us what it's costing you? Just curious. Up here, custom maching runs well over $100 per hour plus set up time.

July 30, 2013, 06:29 PM
I have no experience operating a mill, and only a basic knowledge of practices, tooling, tramming, etc. from my work, so this will be a learning experience. The work I'll be doing is nothing special (only what is required to finish an 80% lower) so I expect it to be more time consuming than difficult.

The mill arrived today - just finished cleaning it up, assembling the little odds and ends, and cranked it around a bit. I don't expect to have the vise until tomorrow, so I'll likely spend a chunk of this upcoming weekend practicing on scrap blocks of aluminum. Even though I'll be using a jig when working on the lowers, I'd like to have a little experience with the equipment before diving in.

I don't plan on disclosing total costs during this project, but it can be compared to the cost to finish any 80% lower plus the cost of procuring and shipping the initial material. CB Arms charged the standard price for an 80% lower, I just provided them with the starting material.

August 12, 2013, 08:21 PM
Roughly five weeks from the time I mailed the raw material, the lowers have arrived accompanied by a jig.

Some thoughts so far:

- Overall finish and appearance is good. I like their design visually, but there are a couple areas I may want to comment on once this turns into a rifle.
- Surfaces have been blasted, and appear clean with consistent edge breaks.
- The trigger guard is beefy and seems quite durable.
- Machining marks are only easily detectable (visually) inside the mag well. Having been shielded from the blasting process as an interior surface, it retained some waviness which is quite apparent upon inspection. The surface still feels smooth but has a slight texture.

Next step will be to procure the remaining tools (5/16" end mill, good 5/32" and 3/8" drill bits) and get to work!

August 12, 2013, 08:45 PM
Looking good so far....

August 12, 2013, 10:20 PM
cool project!

out of curiosity, what's the advantage of that material? how much lighter and stronger is it than the mil spec alloy?

August 14, 2013, 08:49 PM
^ Most of that is answered in post #10, but to summarize as compared to a 7075-T6 die forging:

- Equivalent/comparable ultimate strength
- Higher yield strength (~5%)
- Higher toughness (>10%)
- Better corrosion resistance
- 3% less dense

7075-T6 die forgings are pretty good from a mechanical properties standpoint. Assuming no constant loading in transverse directions (stress corrosion), they're hard to beat.

A small, but important consideration is that this material is plate. From a properties standpoint, plate is generally at a slight disadvantage as compared to a die forging because of grain direction and working. If this material (or one in the same family) were forged, it could be expected to be better in every respect as compared to 7075-T6.

Because of the small size and low loads on a lower, it wouldn't make much sense to opt for this material in a production setting unless someone was willing to pay a premium to shave small amounts of weight.

September 7, 2013, 09:54 AM
I finished milling the first lower a couple weeks ago, but just now got around to uploading the pictures. Below are the results of a rather unpleasant 4 hours in a 110 degree garage.

The jig worked well for drilling, but I was less than satisfied for milling. Because it is L-shaped, one side of the lower is exposed and has almost no surface area on which to clamp. My vise (3" screwless from LittleMachineShop) was unable to sufficiently hold the lower under its own force. I ended up using a large C-clamp across the vise to get enough force to hold the jig in place. A couple marks may be visible in the pictures below from when the jig/lower jumped a couple times early on. A fully enclosed jig would have been greatly preferred.

I made an error backing the end mill out which resulted in an indented-looking area in the middle of the right side of the pocket. This is visible in the second picture. After taking the pictures I also took a countersink to each hole to deburr/smooth the edges.

The process took a bit of patience, and even more WD-40, but I'm pretty pleased for my first attempt at real work on the mill. In a couple weeks when the weather cools down I'll finish the second one.

September 9, 2013, 04:44 PM
That looks very nice.

jack p
September 9, 2013, 04:58 PM
Those seem to becomming along nicely, I cant wait to see em up and running.

September 22, 2013, 01:59 PM
Did some practice electro etching this weekend - ended up doing three designs with different technique, stencil adjustments, etc. The first attempt is below, and will be more or less what appears on the finished lower.

Lessons learned:
- For photoresist film, keep exposure to a minimum. The area to be masked (intentionally exposed to light) is much harder to remove with longer exposures. One minute in direct sunlight was plenty. I didn't like having to leave my test plate in NaOH solution for an hour or more just to get the remaining film off.
- The Q-tip technique I saw used resulted in uneven etching, pitting, etc. when I tried it. Instead, I folded up a bit of paper towel to approximately the width of the artwork. Slowly swiping this across the area repeatedly worked much better.
- Artwork/stencil will be adjusted to thicken some lines since this leads a more consistent etch. Font will be enlarged slightly as well to prevent some areas from running together.
- Patience is key. 30-45 min of actual etching per logo was typical.

Prior to etching:

Results of first attempt:

November 16, 2013, 04:42 PM
Just updating to say that I haven't given up. Finished machining the second lower this afternoon and did test fits of pins, trigger, hammer, etc. to verify function - everything is working as expected even though I did remove too much material in a couple areas.

Next steps will be to find a shop willing to bead blast the lowers to clean everything up, then practice anodizing.

December 18, 2013, 05:38 PM
Being functional and anodized, the lowers have reached the end of the road for now. It will be a while before they're turned into rifles.

Lower #1, the gray one:

Lower #2, the orange one:

I'm not satisfied with the results on the orange lower, so I will be refinishing it at some point. The surface prep wasn't equal to that of its gray counterpart, and there are some splotchy blemishes visible in the photo where dye didn't quite take. The anodizing was pretty straight forward, so I'm not too concerned about having to take another run at it.

Lessons learned:

The photoresist film which worked excellent on my flat/ground test plate wasn't so great on the lower. I suspect that the bead blasted surface made adhesion a bit more difficult, since what took 1-2 tries on the test plate took 5-6 tries on each lower. I went through quite a bit of film just trying to get it to stick this time around. As a result of the adhesion problems, the etching also didn't turn out quite as nice (i.e. less well defined) as compared to the test plates. If I were to do this again, I would try a spray-on or paint-on photoresist to ensure complete adhesion and coverage.

If the directions are followed, the "LCD method" of anodizing works very well. That being said, note to self: double check the leads on the anodizing setup. The colored nuts on my power supply were reversed (red on negative, black on positive), and I didn't notice until 30 minutes later. Fortunately, I had a test piece running at the time.

The Harbor Freight mini mill does the job, but that's about all I can say. There's a lot of room for improvement with regards to play, adjustment, etc. on the axes. I don't regret purchasing it, but if I had ~$2k to spare, a larger garage, and a desire to make more chips, I'd be looking for an old Bridgeport.

Spend more time on surface prep. It's worth it to ensure that the surface is uniform in texture and appearance, because it seems that anodize & dye exaggerate any inconsistencies in the finish.

Doing all the work for finishing a lower is fairly time consuming. For one or two off, it's not cost effective either. However, I did learn quite a bit and now have the ability and tools to try some jobs I otherwise could not do. I might be hesitant to mill another 80% lower, but I had fun with the etching and anodizing - would probably do that again. Estimates for my time spent (per lower) are detailed below.

4 Hours - Initial Milling.
1 Hour - Checking fit/function with lower parts kit, and cleaning up milling as necessary.
2 Hours - Designing, sizing, and printing vector artwork for electrolytic etching.
2 Hours - Test etching of artwork. Includes setup of equipment and few minutes of intermittent downtime while chemicals do their thing.
1 Hour - Surface preparation (blasting) and cleaning of part.
3 Hours - Anodizing process from deox/desmut to final dye.

December 27, 2013, 10:13 AM
As an Aggie, I of course think you should've gone maroon instead of orange, but they both turned out quite well. You going to do an upper in .458" SOCOM next to show your customers what your material can do?

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