6061-T6 VS 7075-T6 BILLET LOWER
In the world of metallurgy, aluminum is given a numerical identifier that refers to its properties. When referring to aluminum, the alloys that make up a particular series of aluminum can make a difference in its strength and performance. (Hence the debate between 6061 vs 7075 aluminum.)
Many Ask what is better between 6061 and 7075 Billet Lowers and how do I chose what is best for me? It is obvious that the price is generally much better for 6061 Billet Lowers then 7075 but why and does that mean its not as high quality material as a 7075 Billet lower?
Indeed 7075 is a Stronger Material (Aluminum Alloy) then 6061, but is this strength difference significant? 7075 Billet is a very popular material for making lowers and is the Mil-Spec which is why many people assume that it what they want and if it is good enough for the military then it is good enough for them. The truth is the Lower receiver of the AR-15 and AR-10 style rifles are designed where they do not work under a large stress load and whereas all of the High Pressure function takes place in the upper receiver and in the gas system. It is debatable if the strength differences between 6061 and 7075 is even significant enough to notice any difference.
It has also been shown that 7075 Billet Lowers while technically stronger are also more ridged and will shatter or crack under a huge stress, whereas the 6061 Lower is a softer metal and during rare malfunctions it indents or bends with the stress and it can be argued in some instances this is a better outcome then cracking. 6061 Billet also has proved to me more corrosion resistant.
Although the alloys that make up 6061 lowers and 7075 lowers are similar, the actual amount of alloy agents making up each individual composition is significantly different. The composition of 6061 aluminum includes magnesium, silicon, iron, copper, zinc, titanium, manganese, chromium and such like and the composition of 7075 aluminum consists of the same alloys but differs in the amounts of magnesium, silicon, iron, copper, zinc, titanium, manganese, and chromium, and additional metals which make up the series.
Below are individual links to that better explain these differences
The 6061 vs. 7075 Billet Lower debate will continue for time to come and it really boils down to personal preference. If you are a true enthusiasts that wishes to stick to the strongest Mil-Spec metal and price is no object then stick with the 7075 Billet as it will give you a piece of mind knowing that you are using the strongest metal. If you are a budget conscience builder then the 6061 Billet is probably your answer and not to worry 6061 Billet is a common and very high quality retail for AR15 and AR10 80% lower receivers and will suit you well.
If you want to follow more of what people are saying about this debate a good thread can be found below: