When it comes to AR-15s and M16s, there are two materials that the metal is made from: 6061 and 7075 grade aluminum. But what the heck is the difference between these two, and more importantly, which is better.
First, what’s up with the numbers? Simply, cast alloys are all given a four digit code that signifies the type of the composition of the metal. 6061 is made from: Aluminum, Magnesium-Silicon while it’s counterpart 7075 is comprised of: Aluminum, Zinc-Magnesium.
Now, concerning the T6 suffix, the T stands for thermally treated temper metal, and the 6 represents the fact that the aluminum was solution heat treated and artificially treated.
These differences in metal composition play the main role in determining the strengths and weaknesses of each aluminum grade. The most important differences to consider when comparing these grades are: Formability or Workability, Weldability, Machining, Corrosion Resistance, Overall Strength or Resistance to Breaking, and Typical Application.
6061-T6 Grade Aluminum
Formability or Workability: Good
Corrosion Resistance: Excellent
Typical Application: Structural
7075-T6 Grade Aluminum
Formability or Workability: Fair
Corrosion Resistance: Average
Typical Application: Aerospace
So what does all of that mean for you and your particular AR-15 build, and which 80 lower receiver grade is actually superior?
That is up to what you intend to do with your AR-15, in what type of environment you live, and simply personal opinion and preference.
First, weapon intentions. If you plan on firing your weapon more than the average person, you might be better off with the 7075 for its strength. Firing your weapon to excess will result in your needing to ensure your lower is strong enough to bare the impact of constant firing. Having a stronger grade of metal in this instance is a better option.
Though, if you plan on practicing with your weapon maybe once a month or so, you would easily be able to get away with the 6061.
Second, If you live in an incredibly humid or wet environment, it would be better advised to go with the 6061 for its higher corrosion resistance. Though the 7075 grade metal would be fine, as long as it is kept in a case, or cleaned often, especially directly after firing. We always recommend anodizing your Ar-15 to help with further corrosion and wear as well. That is a very important step to help with the longevity of the rifle.
And finally, personal opinion and preference is the real determining factor here. If you want a completely custom made lower with engraved designs and other fancy additions, builders will use 6061 due to the ease associated with the material. 7075 aluminum can still be used to customize your AR, the process is just a little more challenging due to the increased strength.
Some operators are completely against 6061 because of its lower strength. There are a select few operators that firmly believe that the only option for metal grade is about strength, nothing else matters. If your weapon is strong, you need not worry about anything else such as the other pros and cons.
But this is completely up to you, your personal needs, and opinion on the matter. Both grades of aluminum are a great option, it just depends on what you prefer for your particular build.