ar15 stripped lower specs

[metalguy]

mchaley: I am new to the AR game myself, (just assembled my first one last night, EASY) but I make, and repair aircraft parts for a living. Let me fill you in on a few things reguarding aluminum alloys: The numbers 7075, or 6061 refer to main alloying elements composing the aluminum alloy. 7XXX series is alloyed with zinc, and 6XXX is alloyed with silicon. I know this means nearly nothing to the layman, however, both are quality, heat-treatable aircraft alloys. (never heard of 7076, but I am sure somebody may make it) The differences are indeed in hardness when heat treated. BOTH can be made dead soft, but the 7xxx series can be heat treated to a harder, and tougher degree. The advantage 6061 has, is it is a weldable alloy. IF it breaks, it can be repaired by welding. 7075 cannot. 7075 can be machined to a finer finish, due to it being able to be harder. 6061 does have better corrosion resistance, but do you leave your weapons out in the rain with no coating?? It is basically a moot point, unless you are into abusing the firearm, and the barrel would probably be the worst off anyway. I hope this helps. I know it is an old post, but I ran across it when looking into partially machined lowers. I am looking at getting into making one for myself.------Metalguy

[orionz06]

I think most other companies use 7076 T6 as well. Sun Devil, my favorite company right now, makes their stuff out of 6061 and some people think it's "soft" because 7076 is harder. However, here's another opinion from a gunsmith: "6061 aluminum has some significant advantages over 7076. While 7076 is "harder" than 6061, it is more brittle. 6061 has a lot more "give" and resilience. 6061 is also more corrosion resistant."

Gut feeling is that you get what you pay for. I don't know how many you want to build, but if you are going to build just one or 2, why not get a lower you really want, RRA, Sun Devil.

Al

Bear in mind that the anodic layer is what really matters in terms of hardness. Corrosion resistance will only matter once you wear through the anodic layer, and if you have concerns about hardness to begin with, you are probably the first. Look at some of the NFA lowers out there that pump thousands of rounds a day at machine gun shoots... They seem to be doing fine.

[metalguy]

Anodic hardness refers to an anodized coating, and has nothing to do with material composition. Hardness refers to the rockwell scale, and corrolates to tensile strength of the aluminum, not a surface treatment like hard anodizing. 7075 can be hardened to a much greater degree than 6061, and is a structural material on many airframes. Either 6061, 0r 7075 are good choices for a material in a lower, as long as they have been heat treated properly. Any quality finish will do. (anodizing, etc.)-----Metalguy

[orionz06]

Yes, but the aluminum hardness may be less relevant if anodized properly.

The other concern about the billet lowers is do they check to ensure they are getting any particular hardness?


ETA: I need to find a hardness tester... I have some anodized parts I wanna try... 6061 T6, 6061, 7075 T6 hardcoat anodized, 6061 hardcoat anodized, and a few other odds and ends... Time to play the alumni card at PSU

[metalguy]

I have access to a Rockwell tester. We use it to see if parts were heat treated properly. Basically the only way to tell, as the part stays the same color, no matter the temper. 6061 "O" will be about the same as 7075 "O", but T6 will come out different. Hard anodizing will definately change the results, as it will make the surface harder. It would be interesting to see results on hard anodized "O" aluminum alloys. Generally, a part will heat-treated before any machining processes, as quenching afterwards can result in some major warpage due to water quench. -------Metalguy

[orionz06]

My guess is the anodic layer on good anodizing will have a pretty big impact on the test, but its brittleness concerns me (the oxide layer that is). If you by chance test anything do let me know the results.

[metalguy]

I can indeed test some of the alloys, but I am afraid we do not have any that are anodized. But at least, I can test some of the alloys, and save some time on re-testing known properties. I will post results here.----Metalguy

[orionz06]

Lemme see if I have anything that I know for certain is anodized to any particular requirement that I can send you. What interests me most is the hardness relative to bare metal.

[metalguy]

Ok, I FINALLY got some aluminum tested. I tested 7075 T-6 and 6061 T-6.
The 7075 was 81.1 on the "B" Scale.
The 6061 was 61.5 on the "B" scale.
So, approximately 20 points on the scale's difference in hardness.
(I was testing some 4130 that we had just hardened, before tempering. It came out at 52.3 on the "C" scale, way too hard for its purpose, so we tempered it, and it came out just under 30, perfect.)