7075 T6 Aluminum Receiver

Someone local is telling me not to get Aluminum Receiver. I dont know anything about it. Looks to me that Smith has all of there M&P AR's with these receivers and I don't want anything but a smith. Any opinions on this?

Besides it's fine, the Smith design works well, many companies use aluminum.
I have almost 1000 rounds through mine in just a month with no signs of wear in the receiver.

I have a pre-ban AR-15 sitting in the safe....very much an alloy receiver. Were they ever made from something else?

There is no reason to listen to someone local telling you such things. Next thing you know, they will be telling you that a forward assist and dust cover is required else the AR won't shoot!

2001gmc said:

Someone local is telling me not to get Aluminum Receiver. I dont know anything about it. Looks to me that Smith has all of there M&P AR's with these receivers and I don't want anything but a smith. Any opinions on this?

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Ask this person what he thinks a "good" receiver is made out of. Pixie Dust? Moon rock? Unobtanium?

Then tell this person to do even the most basic of research on the construction of ARs before offering any more advice on them.

There are some lowers made of plastic that are not the 22lr. Plum Crazy, and Vulcan/ Heese. Pass on them. Too many issues, and the cost saving is minimal at best.

I will give you a little schooling on alloys (Aloominium!! )
There are uppers, and lowers made of 6061, and 7075. FWIW, 7075 IS STRONGER. The strength runs near the 70,000 psi range for tensile strength. 6061 is in general near the 60k mark. Lots of grades of aluminums. As in: 6061 T6. The T6 is the age hardening on the aluminum. A T65 is hard, but has some different qualities that make it more formable; ie bendable. It will work harden, meaning as you bend it (Work it) it will stiffen and then SET in the place you bend it. If you try to bend it substantially more, or try to bend it back? It's going to crack.
Machinists like 6061, as it is easily worked, has good weather resistance as well as chemical resistance, and it is EASILY WELDED. This becomes a big plus to certain gun builders who are looking to experiment and radically alter and customize their rifle parts.
7075 is very durable; it's about the strongest aluminum made. It is usually a cast material. It has great properties for wear resistance, and as such, it is very much preferred for moving mechanism housings. (Rifle parts qualify as such.) 7075 is more rigid, and resists bending and flexing much better than cast 6061. It also has great weather and chemical resistance.
The one drawback to 7075 is that due to its' hardness, it does NOT like to be welded. Billet, extruded 7075 is grumpy stuff to weld. And, it cracks more than Whitney Houston partying with Charlie Sheen!
Cast 7075 CAN be welded, but it is usually a specialist who would do this, and I will say, it will NOT be a structural weld, so do not stress that part.
For say a rifle lower, yes you could get away with welding up a cracked magwell (Ask me how I know!) But it will always be less than it was. I have welded a lot of aluminum in my time, and the worst project is trying to graft unknown aluminums together, ie 6061 and 7075. The materials fight each other usually, and the weld fails.

Now, with all this said: If you were to be experimenting with side charging, or belt feeding experiments, then I would say get 6061 parts to work with. Once you perfect it, a 7075 unit would be stronger in the long run UNLESS you had to add material to create a port, mount plate, lock or release type of mechanism. Or, if you had to add beef to make it hold more pressure. (This last scenario requires a very experienced welder who is rather meticulous in prep work, lest you see a weld fail at the most inopportune time.)

For box stock lowers, both are fine. For uppers, 7075 is preferred because of superior wear resistance.

Thanks for the replies all.

Rojodiablo...I just wanted to tell you, I couldnt do a double like on that last post. But I will 5 star this thread. Thank you sir!!!

rojodiablo said:

There are some lowers made of plastic that are not the 22lr. Plum Crazy, and Vulcan/ Heese. Pass on them. Too many issues, and the cost saving is minimal at best.

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What issues? I was unaware of Glock, M&P pistols, Ruger and others having issues with using plastic on their guns.

crracer_712 said:

What issues? I was unaware of Glock, M&P pistols, Ruger and others having issues with using plastic on their guns.

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Handguns & rifles behave differently and deal with different stresses.


I don't believe that there is a functional issue with the Plum Crazy lower. It mates to uppers & functions fine. Pull trigger, rifle goes bang.

I've looked over a used Plum Crazy lower at my LGS. The take down pin, pivot pin, hammer, and other parts are polymer. It's just something different. Being a 15-Sport owner, I'm not one to knee-jerk poo-poo something different.

I think what people take issue with is that the polymer flexes during the firing cycle.

PlumCrazy AR15 / M16 Complete Plastic Lower Assembly - REVIEW - YouTube

The individual who put together this video did a good job. He has slow-mo video of the Plum Crazy lower v.s. traditional lower with a compensated & non-compensated upper.

Supposedly, new frontier armory has a new polymer blend that's stronger than the plum crazy, which is currently under going a name n logo change to enhance their image better for military and police sales.

crracer_712 said:

What issues? I was unaware of Glock, M&P pistols, Ruger and others having issues with using plastic on their guns.

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No, the pistols have not really had many issues. ( My roommate had to send his Glock back because the lower cracked on the rail for the upper glide. This is a known warranty issue for Glock .40 cal pistols, especially those with heavy use. )

Now; on to the Plum Crazy, Vulcan/ Heese unit. AR's bolts throw a LOT harder than say a 9mm or a 45 ACP. Back, and forth with more force. The PC lowers tend to crack around the take down pin holes.
For the 'Safe Queen' that will go to the range and throw a couple dozen rounds a month? You might not see the issue for several years.

But don't think for a second these lowers are built to take the kind of day to day beating real carbine shooting places on parts.
With lowers available from time to time for about $55 on super-sale, and average prices between $80-100.... there is no practical reason to buy a lower that HAS SHOWN a propensity to crack at the pins. The plastic used needs more material around those pins. That means a different mold. That means THOUSANDS of dollars in mold design, and then parts testing.

I work with a small vendor at the Crossroads gun shows. We have sold lowers and swapped parts for 3 cracked lowers since October, 2011. It's not that I want to be down on the part, but it's a Yugo that fires bullets.
While I am at it doing my best to get on the "Do not send Xmas cards" list........ Phoenix Arms 22 and 25 caliber pistols are worth more as recycled material than they are as firearms.