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AR Receivers: 7075 T6 vs. 6061 T6 Aluminum

The AR 15 market is absolutely massive. The weapon’s popularity, and certain politicians’ war against it, has propelled it to become the most popular rifle in the United States. Its popularity is a blessing to you! The free market has expanded so much so that you, the at-home black rifle builder, have AR 15 parts for everything: Barrels, handguards, new calibers, stocks, magazines, accessories, and of course, the meat of it all, lower receivers. It isn’t as simple as choosing between polymer and aluminum. It goes deeper than that – there are even different types of aluminum AR 15 lower receivers. For brevity, let’s focus on the two aluminum alloys that make up most of the market: 6061 T6 and 7075 T6 Aluminum. 

7075 T6 and 6061 T6 AR 15 lower receivers explained

So, what’s the big difference in materials used for AR 15 lower receivers? What’s with the 4-digit codes? All great questions, and we’ll answer them all. Both 7075 and 6061 have historical connections to the AR series of rifles. The first ArmaLite Rifles (which became the M16) utilized 6061 T6 lower receivers. The M16’s initial release was disastrous and one of the first things re-tooled was the lower receiver: It was reconstructed with 7075 T6, and it’s remained so since then. 7075 T6 is “mil-spec”, like a grunt’s M4, but 6061 T6 is making a comeback. Why?

The T6 Designation

Before we explain the 4-digit difference, Let’s explain that “T6” compatibility: It simply means the aluminum alloy has been tempered by heat. Heat strengthens the alloy and makes it incredibly hard and tough. T6 designations are important for aluminum materials because they bring the aluminum to its highest point of strength and durability. This doesn’t mean all aluminum alloys that are T6-designated are created equal. It just means that they have reached their highest level of strength possible in that particular aluminum alloy blend. 

7075 Alloy

Alright, let’s get into those other numbers: 7075 is an aluminum alloy that uses zinc as the primary metal. 7075 aluminum is incredibly durable and has a very high tensile strength and overall high strength-to-weight ratio. It’s generally used for aerospace applications and features average corrosion resistance. Its strength can also be a weakness: It’s generally more difficult to mill a 7075 AR 15 lower receiver. Is this a big deal? Not too much – it simply takes a little longer to finish your 80 lower receiver, but we don’t consider it overwhelming. 

6061 Alloy

6061, like our new Premium Billet lower, is an aluminum alloy that utilizes magnesium and silicon as the primary metalloids. 6061 isn’t as strong as 7075, but it is still very durable. As a shooter, you won’t notice any differences between 6061 or 7075 AR 15 lower receivers. The difference you will notice when machining your own 80 lower is that 6061 is easier to mill. It will take less time than a 7075 lower. 6061 also provides high corrosion resistance, which is nice if you ever damage your lower’s phosphate or anodized finish. Both 6061 and 7075 AR 15 lowers have strengths and weaknesses. The differences aren’t noticeable to most shooters, but trust us, we know that feeling of wanting “the best”. In the land of 80 lowers, the differences matter a bit more. 

Want an easier time machining with your 80 lower jig? Go with 6061. Want the toughest, roughest lower with a little more time and sweat spent machining? Go with 7075. The good news is either will function for the lifetime (and longer) of the user without serious issue. Don’t get too wrapped up in the differences between the two metals, just know they both function well. Go with what fills your needs and wants. 

Our most popular 80% lower 5-pack comes with 5 beautifully machined, forged 7075 T6 receiver blanks – they’re just waiting for your final touch with a jig! That equates to just $56 a lower – on average, that’s half the price of any other finished lower. 

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