80% AR suggestions wanted

Been leaning toward adding one or more AR's to the stable. Just read the "Why is the AR so popular" thread. I'm not a gunsmith, 'though I've had a few apart and back together, and have made gun parts that worked. Fairly experienced general manual machinist.

What do I need to know to pick out of the vast marketplace, good values in 80% lowers and necessary jigs and/or drawings?

I used these dwgs and data and it came out well. http://www.ray-vin.com/tech/lower.htm

RWO

80%'ers are just like finished lowers, only.... well.... unfinished.

Meaning you need to decide if you want forged, cnc milled, material, and annodized or not.

As for jigs, why even bother? This is a machining forum, don't you have access to a mill?

I do have a horizontal mill with vertical attachment, dials on feed screws, and indicators for a double-check, so can locate holes by X & Y from a datum....But a jig might make secure holding of an odd-shaped piece easier and more rigid. Lord knows I fixture and determine datums of enough weird-shaped pieces, but nobody sells a fixture to rebore a broken, welded and warped tractor power-steering-box, for instance,. No need to re-invent the wheel or make a job hard just because I can.

So, I would assume a forging is both better and cheaper than a milled-from barstock, because it is a fast way to get near-net shape and gives better grain flow....unless you need too few of a shape to justify forging dies, which is not an issue here because want just the same interchangeable part as X million others.... Wrong?

I suppose I want 7075 T-6 because it is the strongest common Al alloy, not noticeably less machinable than the alternatives? Wrong?

I suppose I would mess up any anodizing already done, so there seems little point to paying for it......Or does anodizing improve function or life of surfaces that I would not cut doing the last 20%?

Is there variation between manufacturers as to WHICH 80% they do, and which operations are left for the end-user?

If I were planning production, I'd try a few from many different sources and compare, and plan to throw a few away, but I'll probably do only 1 or 2, so I am hoping to stand on the shoulders of you giants.

Stop giving a shit about the strength of the lower receiver. All it does is hole the trigger and hammer in the right place and give the buttstock somewhere to screw on.

The -only- metallurgy factor that comes into play is how soon the pin holes start to wear and wallow out. If you're just gonna shoot a couple boxes of ammo a couple times a year, I doubt it matters. If you might shoot a couple thousand rounds a year, you'll care. If you don't anodize the holes, you get much less life out of them as well.

Forged and Milled makes no difference really. You'd probably have swapped the barrels 3-4 times from shooting them out before you have enough wear and tear to see any difference between the performance of milled vs forged if there is any.

Worry about the shit that matters. BCG and Barrel.

Otherwise, it's just a hunk of metal, don't think about it too hard.

I used Daytona Tactical - seems nice enough. I did buy the jigs just for an additional reference point but we didn't really use them. I'm sure the forged lowers will last longer if you're gonna shoot a ton. For me it's just a few boxes a year so no big deal.

As far as wallowing out the holes, when mine wear out I will just machine and install drill jig bushings - problem solved! They'll never wear out again.

Joe Miranda said:

As far as wallowing out the holes, when mine wear out I will just machine and install drill jig bushings - problem solved! They'll never wear out again.

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FUCK, I wish I thought of that when I was working for gun mfrs still. We could have upgraded shit with precision-ground carbide bushed holes for the ultimate in wear resistance for the high speed, low drag operator who needs the utmost in reliability while operating in dynamic non-permissive environments.

Buy the drill jig bushings for $3 ea, sell them as a kit with a cheap reamer for $75 (or $125 with a anti-walk pin upgrade) and make bank, baby.

magneticanomaly said:

I suppose I want 7075 T-6 because it is the strongest common Al alloy, not noticeably less machinable than the alternatives? Wrong?

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It's harder and less sticky than 6061. So to me, it's easier.

If you go with an 80% lower, buy one that is already anodized. A lot of ano shops won't touch a lower from the average Joe garage machinist. As for holes roundin' out, you'll have to put a lot of rounds through her before you see problems if any. The drill guide bushings would be a nice touch though........................

JNieman said:

FUCK, I wish I thought of that when I was working for gun mfrs still. We could have upgraded shit with precision-ground carbide bushed holes for the ultimate in wear resistance for the high speed, low drag operator who needs the utmost in reliability while operating in dynamic non-permissive environments.

Buy the drill jig bushings for $3 ea, sell them as a kit with a cheap reamer for $75 (or $125 with a anti-walk pin upgrade) and make bank, baby.

Click to expand...

Man, if you can work "Billet" "Aircraft Grade" and "Mil-Spec", in there, you'd about have all the hot buttons covered!

While worrying about which alloy to buy is fashionable, I suggest a look around Youtube for the video of the lower made from Ikea cutting boards. It pretty much only matters if you are beating locks off doors with it (in which case, it breaks no matter what you made it of). OK when the outfit is buying, not so much, when it's your own.

Unless you really need one that isn't on anyones books these days, for which purposes I would likely look hard at the bolt together units, there seems to be so many guys making lowers that the cost of an 80 percent unit is more than a finished one, it seems. Dunno how many guys are trying to make up for losing money on every unit, by the increased volume, but there seems to be no end to the choices. Can't be a lot of margin for the guys that are doing anything but putting otherwise idle machines to work.

The real money savings is in just buying a block of material and carving one, though that is the long row to hoe.

Cheers
Trev

Here is a link to one of my older builds. ArcaneIron.com • View topic - AR 8% lower build

The current ones I'm working on I went with the "raw" casting as I plan to try and use a Ceracote finish on them. It requires more equipment though, sand blaster, paint gun, and misc.

Hope it helps.

-Ron

7000 series might have higher tenisle numbers than the 6000 series does

But it corrodes from the inside out.

It doesn't anodize as well, but the "big boys" have that figured out.

Get an 80% lower with mil-spec (catch- word!;-) anodize . Use paper when you clamp.

They come out Perfect! Al2O3 is some tough stuff!

CalG said:

But it corrodes from the inside out.

It doesn't anodize as well, but the "big boys" have that figured out.

Get an 80% lower with mil-spec (catch- word!;-) anodize . Use paper when you clamp.

They come out Perfect! Al2O3 is some tough stuff!

Click to expand...

Yea, "mil spec" used in the case of anodizing is one of the few places where it actually has a useful and very important difference. If they will certify that they are anodizing it to MIL-A-8625 Type III hard-coat anodizing, then you know it's what you want, and they didn't do some half-ass bullshit.

The anodizing makes /all/ the difference on the receivers. It's most of why you can get great life out of aluminum.

I don't know why you brought up 7000-series corrosion though. I've shot some very old M16s and, while I wasn't specifically looking for corrosion, I couldn't tell a difference between them that would make them seem inferior. I do not believe there will be an issue. To be honest, I never heard that about 7000-series in general.

Regarding the draw back of the 7000 series alu. It's from experience, observations and education of my aircraft days. And just thrown out as a counter to the "7075 is stronger, it must be better" comments so often parroted.

Used in the application of this discussion. More than likely there will never be an issue. But if I were building an "heirloom", I would use the 6000 series ....;-)

I'll take 7075 any day of the week over 6061. You can pretty much machine it without coolant. I don't know who is doing your ano, but ours does just as good on 7075, 7050, and 6061

Anyone ever machine 7050 T-7 alum? That is by far my favorite.

Email Sam at S+S Fabrication in Ardmore,Tn. He makes nice, machined 80% 6061 lowers, and a really nice jig. [email protected]

I go through over a 2-3000lbs of 6061 and a 4-500lbs of 7075 a month. Sure 7075 is less corrosion resistant than 6061...................but lowers are ano'd, so who cares. As far as fatigue/stress cracking, lower design is such that it is non issue. 7075 machines like a dream compared to 6061. And even the crappiest 7075 will cut 10x better than the best 6061. By this I mean there is 6061 and there's 6061. The cheap Chicom garbage cuts like bubble gum. As does some of the material that comes from eastern Europe. Stuff from US producers even varies quite a bit. SCM, Sapa, Kaiser are all US extruders. I will only allow Kaiser on my floor. It is the least likely to cut like crap. I still run into troubles from heat number to heat number. Poor finishes, chip control problems, hard/soft spots. I have never had issue with 7075. From Alcoa(US) to Slavako(European) is all cuts pretty darn good.