Anodized vs Unanodized durability

[MAHLMAN]

I read various things in regards to anodized vs unanodized lower and upper receivers. So yes hard coat anodizing as a layer of protection is more durable then bare aluminum. Especially on 6061. 7075 is pretty tough stuff in comparison.

So on uppers where you read about facing/truing the end of the upper for a true 0 degree axial fit to barrel. So now you have removed this tough surface but to me the metal would deform under the surface anyway so what do you really gain with doing this. Having a 7075 upper would seem to me to be the really important thing.

Then we have the lower. On an 80% lower you will have trigger group and safety holes without anodizing. How many rounds does one shoot before you can wallow those out enough to be a problem with 6061 lowers?

I am assuming that 7075 lowers will be much more resistant to wear. This is a subjective opinion based solely upon working with 7075 in machining where it is pretty amazing how hard it is. But there is a difference between tough and hard and something hard can still be abraded more then you might expect.

So what is the durability limit on unanodized vs anodised 6061 and 7075 upper and lower receivers? If I can egg a hole in 1000 rnds I am concerned. If it takes 20,000 rnds I am not

 

[JS8588]

Cerakote it and don't worry about it

 

[redneckbmxer24]

I’ll start by saying that I’ve never had an 80% lower so I cannot speak to how many rounds it would take to wear out the pin holes. I’m sure some will have an issue with that but unless you have pushed one to the point of failure then STFU.

Type 3 anodizing has a vickers hardness of 350+, 6061T6 is 107, and 7075T6 is 175. So anodizing is at least twice as hard as bare 7075 and over 3x as hard as bare 6061.

One of the reasons I’ve never owned an 80% is because I do not believe bare aluminum has the surface strength for it. Never mind the fact that the holes cut with a jig aren’t going to be as uniform as those done on CNC. The other reason is because I’m not poor and DGAF if the government knows I transferred a receiver.

If you insist on an 80% a simple work around to the pins wearing out the holes would be KNS pins. It’s still going to wear faster than anodized pin holes but at least you’re taking the rotational wear out of the equation.

Personally I’d just buy a quality lower receiver, it’s one of the cheapest parts of the gun and you can get one for less than the cost of an 80% lower and the janky jig kit and never have to worry about the lack of anodizing.

As far as the uppers it’s the same thing, buy a quality receiver and don’t worry about facing it. Anyone who thinks they’re doing any good by facing a quality CNC machined receiver with a $30 Chinese tool on the end of a dewalt drill in their garage is a fucking idiot.

 

[LRRPF52]

Agreed on the hardnesses and anodizing, which acts like a case-hardening for aluminum. You can still anodize once you’re finished machining an 80%.

The problem with receiver faces out of square isn’t the machining, but the anodizing thickness coming out uneven. I’ve had this conversation with some of the big names in the industry about it, and it is a problem if the anodizer doesn’t ensure a uniform surface after the process.

There’s no way to really machine it out of square unless you purposely drilled cock-eyed through the upper and created different thickness walls of varying thickness for the raceway.

But squaring the receiver face is not for idiots. When I go to zero my optics, I’m so close to mechanical zero already and the groups don’t lie before/after.

When I first learned of the process from one of the AMU armorers, I trued-up several uppers and bedded the barrels. I made rifles that were shooting 1.7” groups shrink to .3” to .75”.

 

[MAHLMAN]

Holes are not a problem for me as I do them with a 1/8" end mill and a helical tool path and can accurately locate them with a Renishaw probe off the pivot pin hole. This is more of an academic exercise then anything as I can find finished OEM lowers cheap enough by waiting for blems or sales.

I had thought about something like the KNS pins but wondered if they would induce pin wear with trigger parts. I will probably never shoot an AR enough to have to worry about any of this but the machinist side of me still wants to know.