I just noticed that the upper part of a Stag Arms 2TL is made of aluminum.  Is that bad, and will it shorten the life of the gun?  And if so, by how  much.  I've always heard that Stag are quality ARs, but aren't most AR uppers made of steel?  What would be the advantage of aluminum other than a weight savings?  Thanks.

Weight savings is your primary reason and I think all uppers are aluminum, usually 7075 (not sure of the temper) and  they are hard coat anodized giving the aluminum surface toughness/protection.  The receiver provides a place for the BCG and trigger group to reside.  the initial pressure is contained by the chamber and bolt and then the barrel.  there are no issues with an aluminum upper through normal use.  I'm quite confident that your Stag will be fine and unless you shoot a ton of ammo, it'll outlast you.  I'm also confident that one of the more knowledgeable members will add to this.

That is very helpful––thank you!  Actually, I just read where the lower is aluminum too unless I'm mistaken.  Is that common on all AR's as well?  Thanks again!

yes aluminum.  READ the history of the black rifle, google/wickepedia etc.  Don't be afraid to ask questions, after you've read a lot.

Yes, upper & lower receivers and the extension tubes are aluminum.  Barrel, BCG and small parts are steel.  Most of the furniture (handgaurds, grips, stocks) are plastic.  I'm sure people can come up with exceptions, but that is typical and almost all AR's.

I'm sure you have your answer but I thought I would add to it. I bought a DPMS and replaced it with a Stag Arms LH Upper. The reason they use 7075-O and T6061 is for their light weight and non corrosive attributes. If your whole firearm were made of steel it would be so heavy you wouldn't want to carry it long. If it were made from light weight steels or precious metals such as titanium it would be considerably more expensive. There are many uses for these alloys such as Aircraft fabrication, missile parts, aerospace and defense applications. I have had mine for quite a while and have had no troubles. Have fun and be safe

Mil spec rifles are 7075-T6. Cheaper ones are 6065. Only a couple of manufacturers make steel or Ti receivers.

Excellent information from Everyone and super helpful!  Thanks gang––you guys are great!