Ok, I ahve a question for someone less "metalurgically challenged" members of the forum. It seems that AR receivers (at least all the good ones) are made from 7075 T6 forgings while most railed handguards, sights, and other accessories are machined from 6061. I know that 7075 is much harder than 6061 and I realize the receiver needs that strength, but are there other reasons for the difference?
Ar Aluminum question....7075 and 6061 receivers vs. rails
- Thread starter Servo77
- Start date
The massive pressure forces experienced during firing an AR are contained by the bolt and barrel extension. Plastics and carbon fiber have been successfully used for AR receivers, so strength is not the issue. The most important function of the receiver is to hold the barrel and bolt carrier in alignment. This requires stiffness. A thick walled 6061 machined billet or extrusion is stiffer than a thin-walled 7075 forging.
The "stiffness is better" philosophy rules in benchrest shooting, where a 0.1" group wins and a 0.2" group loses. There, you'll find the firing line filled with thick-walled 6061 receivers and a tiny number of steel thin-walled receivers.
The "stiffness is better" philosophy rules in benchrest shooting, where a 0.1" group wins and a 0.2" group loses. There, you'll find the firing line filled with thick-walled 6061 receivers and a tiny number of steel thin-walled receivers.
Metal Alloy
I work as an aircraft structural maintenance troop, so hopefully I can help you understand the metals a bit and why they're used as they are.
7075 aluminum is alloyed with zinc (among others) which makes it very tough and it has a high strength to weight ratio. It's used for highly stressed parts and when strength, toughness, stiffness and stress resistance are desired. And just a little FYI, it's a PITA to weld also.
6061 is alloyed with higher concentrations of magnesium and silicon, which gives it good workability with relatively high strength and corrosion resistance. In comparison to 7075, 6061 is fairly simple to weld because it has good joining characteristics.
Working on aircraft I've used these alloys for repairs or replacement parts. Depending on what you want the piece to endure will depend on which metal alloy you will use. For anyone who wants to see the scientific data for material compositions of metal alloys (and many other materials as well) I like
Matweb (http://www.matweb.com/index.aspx)
Hope this helps.
I work as an aircraft structural maintenance troop, so hopefully I can help you understand the metals a bit and why they're used as they are.
7075 aluminum is alloyed with zinc (among others) which makes it very tough and it has a high strength to weight ratio. It's used for highly stressed parts and when strength, toughness, stiffness and stress resistance are desired. And just a little FYI, it's a PITA to weld also.
6061 is alloyed with higher concentrations of magnesium and silicon, which gives it good workability with relatively high strength and corrosion resistance. In comparison to 7075, 6061 is fairly simple to weld because it has good joining characteristics.
Working on aircraft I've used these alloys for repairs or replacement parts. Depending on what you want the piece to endure will depend on which metal alloy you will use. For anyone who wants to see the scientific data for material compositions of metal alloys (and many other materials as well) I like
Matweb (http://www.matweb.com/index.aspx)
Hope this helps.
That's a laugh. I've seen lots of broken plastic AR lowers. I handled one of those piece of crap carbon 15s one time and wanted to puke. I went to firmly seat a mag and the mag blew right past the mag catch and up into the upper receiver. :barf:
Plastics might be adequate for hobby guns that won't see any fighting style weapons manipulation, but they suck for anything more. Any external force such as buttstroking or falling on/dropping your AR if you were climbing an obstacle, and that junk will snap like a twig.
Bartholomew Roberts
Moderator
I think the key area I'd be concerned about is the receiver extension on the lower. This is the area that the military upgraded and reinforced in the transition from the A1 to A2 and I'm sure they didn't do it just for kicks.
As far as recreational shooting, the receiver is not a component that sees a lot of stress and you can use a wide variety of different materials to do that job.
As far as recreational shooting, the receiver is not a component that sees a lot of stress and you can use a wide variety of different materials to do that job.
RockyMtnTactical
New member
The Cav Arms lowers work well. The other polymer receivers out there dont have quite as good a track record though.
I happen to have one of those Carbon 15's - pistol with flueted stainless barrel. It's a fairly rugged gun. It's even pretty accurate. I've blasted thousands of rounds through it with no breakages. It's fun as heck to just line up several mags and blast away, one after another as fast as you can. Nothing melts. Nothing breaks. After a few hundred rounds, you do need to clean it for it to continue functioning perfectly. (Oh, well - that's with all DI AR's) Oh, and I only use the very best ammo in it - Wolf steel cased .223 - buy it by the 1000rnd case load.
The Carbon 15 pistol is not something I'd carry with me to war. But, it's not a bad SHTF pistol-thingy. I don't know how you could call the thing flimsey - it's as tough and ridged as a Bushy aluminum beercan-15. Now, I'd rather have a Sig-556 for a .223 pistol....but for what I paid for the thing, I've more than gotten my money's worth out of it.
RockyMtnTactical
New member
demigod,
Not sure if you are aware, but things can break. ANYTHING can break. Let me know though if you find a super light material that is indestructible though, we could probably get very rich together if you can find something like that.
I never said that the Cav Arms lowers are indestructible. I said that they have a fairly good track record. So do forged aluminum lowers, but those break too...
Not sure if you are aware, but things can break. ANYTHING can break. Let me know though if you find a super light material that is indestructible though, we could probably get very rich together if you can find something like that.
I never said that the Cav Arms lowers are indestructible. I said that they have a fairly good track record. So do forged aluminum lowers, but those break too...
ostrobothnian
New member
You can compare the physicals between the two materials here. Try not to doze off. 
6061-T6
http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA6061t6
and here for the 7075-T6
http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA7075T6
6061-T6
http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA6061t6
and here for the 7075-T6
http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA7075T6
If I read stickies on the history of the M16, it was originally 6061, and switched to 7075 for corrosion resistance. Lots of billet machiners use the 6061 as it's easier.
As for polymer, the better makers have been using it for decades, like HK since the seventies. Lots of pistols use polymer lowers, and most of the new Improved Carbine entries seem to use polymer lowers. Add an extruded upper, we could certainly not have forged aluminum at all in the future. If anything, it's a statement of mass material fabrication dating to the '50's. Injection molding and CNC have bypassed forging.
BTW, the Remington Nylon 66 was polymer - in 1962. Never heard anything about breaking one of those.
As for polymer, the better makers have been using it for decades, like HK since the seventies. Lots of pistols use polymer lowers, and most of the new Improved Carbine entries seem to use polymer lowers. Add an extruded upper, we could certainly not have forged aluminum at all in the future. If anything, it's a statement of mass material fabrication dating to the '50's. Injection molding and CNC have bypassed forging.
BTW, the Remington Nylon 66 was polymer - in 1962. Never heard anything about breaking one of those.