If you’ve been shopping around for 80% lowers then you’ve probably centered on these two buzz phrases: 7075 T6 and 6061 T6. What are they? Well, for starters, they’re metal alloys. Specifically, they’re weapons-grade alloys that comprise most of the world’s AR-15s, AR-10s, and a plethora of other firearms. What’s so great about them and which one is better? What are the differences and similarities? Let’s answer all your questions:
7075 T6 Aluminum: What is it?
7075 T6 aluminum is a forged aluminum alloy. It is specifically formulated to boast a strength similar to many steels, and it has excellent fatigue strength and machinability – two attributes critical for building good guns. It contains zinc, magnesium, copper, and less than 1% of silicon, iron, titanium, and other metallic elements.
While 7075 refers to the alloy content, the T6 designator refers to how the alloy is tempered. The T6 designator means the alloy was subjected to temperatures exceeding 842 degrees (F) for several hours before quenching. This hardens the metal and makes it tough.
As far as 80 lowers are concerned, 7075 T6 aluminum is the stuff the military uses to build its own service rifles. Here are some of the pros and cons, the stuff you should care about:
7075 T6 Pros:
- Denser and harder than 6061 T6
- Truly mil-spec – it’s what the military uses!
- Capable of taking more abuse and hard hits
7075 T6 Cons:
- More difficult to machine
- Wears out drill bits and end mill bits faster
- Not capable of making complex shapes easily (less aesthetic)
6061 T6 Aluminum: What is it?
6061 T6 aluminum is, as far as its metallic composition is concerned, quite similar to 7075 T6 aluminum. It boasts similar qualities of strength and machinability, but the process of its creation is wildly different. 6061 T6 aluminum is not forged – instead, it’s cast as a large block of aluminum and then cut into its final shape.
6061 T6 aluminum looks less impressive on paper compared to 7075 T6. It has a lower hardness rating and shear strength, as well as a lower yield point and tensile strength. But this should not concern you. Why?
Because even though it’s not as “tough” as 7075 T6, it’s still more than capable of handling the stress and abuse your AR-15 will endure. Unless you plan on throwing your rifle down a mountainside or busting down doors for the next 12 months at zero-dark-thirty, then you should not second-guess investing in a 6061 T6 aluminum. “Why?” you ask?
6061 T6 Pros:
- Easier to machine
- More forgiving when you make mistakes
- Lengthens the life of your end mill and drill bits
- Can be cast and shaped with greater aesthetics
6061 T6 Cons:
- Less dense and tough then 7075 T6
- Lower shear strength, hardness, and tensile strength
Which Should You Choose?
Either! Sorry to give you such an anti-climactic ending to this comparison, but that’s the truth: Either alloy will work just fine for your 80 lower build and AR-15 project. Both alloys are tough as Hell and can stand up in any environment, including wartime fire fights. Both are still relatively easy to machine and either alloy will produce a rugged, aesthetically-pleasing AR-15 lower. We recommend you try machining both – start with 6061, then work up to 7075. You’ll enjoy the process and you’ll learn more about gunsmithing different alloys, becoming a master AR-15 builder along the way.