11-15-2011, 08:39 PM
There are volumes of debates on the various forums around 6061 vs 7075. To be clear, the spec is forged 7075 of a specific type (T6?). You can have 7075 and not be the correct spec. But most forged receivers in the last couple of years are of spec materials, and made to spec.
Likewise, there are 6061 grades that are comparable to the 7075 spec. There are also advantages & disadvantages to forged vs billet. Grain structure vs dimensional accuracy, etc.
The better billet CNC receivers are made from 6061 comparable in strength to the spec 7075. Certainly approaching the spec, to the point that you don't hear of billet receivers failing in duty. (There have been some failures from people force fitting parts with excessive force. This is strictly due to tighter tolerances on the billet)
Regarding strength of forgings, you have to also account for the fact that the billet material used in AR receivers is forged to make it a billet. so the only advantage the forged receiver has besides the material is any additional strength in the grain from the forging process, etc. It's not like the billet is "butter soft", or cast.
Realistically, Sundevil or better billet lower receivers have given excellent service. I use them on bench guns. For "hard use" guns (or at least those I would like to have hard use capable), I use a top tier mil-spec forged lower receiver. Not exotic, just a known quantity, for sure, mil-spec receiver (LMT, DD, Etc). Upper receivers it's a bit more difficult to find a "for sure" mil-spec in stripped form. After looking at many options for upper receivers, I came back to AA's deal. It's as good as any non-exotic, made from a quality forging, and excellent fit/finish.
There are volumes of debates on receiver material / mfg on other forums. I lean toward trusting some of the armorers with relatively high volume experience in Iraq on one of those forums. Their conclusion- most people worry way to much about lowers. And often spend too much on exotic lowers. Then go and put substandard components in far more critical roles (bolts, barrels, etc) Which do fail, make bigger difference, etc.
My learning from all this is that I used to build lowers and buy uppers. I now do the opposite. I can get a very good mil-spec lower assembled for not much more than I can build one. The uppers, I build with parts that I know the mfg & provenance, using as much "for-sure" milspec as I can.
I want:
- forged 7075 extension/buffer tube, mil-spec threads & dimensions
- Mil-spec lower receiver
- The best trigger group of the best mfg I can get. I'd consider Colt, LMT, or DD as the only standard trigger groups I'd use. DD can be had for the same as generics. There are other std triggers that are probably OK as well, but I go with known mfgs. I don't have as much experience with high end triggers, so won't comment on them.
Don't think there is a difference in trigger components? There are some pretty good side by side comparisons with Colt, LMT, DD, and then the generics. They are not the same! Nearly all vary, some are noticeably better than others in fit/finish.
I found LMT complete lowers provide the above at a reasonable cost. Not much more than I could build one for. DD used to, but they no longer sell assembled lowers. But would also use them or a Sabre one if available. Or one from a Colt 6920, etc. With the LMT you can also upgrade to a very good two stage for much lower cost than adding the same separately.
On uppers, most of my focus is on the barrel & bolt carrier
- specific barrels depending on caliber/usage. 4150 cold hammer forged if in 5.56 carbine. There are less hard duty options for Grendel, and more target options. So for my Grendel carbine I went with an SS M4 profile minus the M203 cuts on my most recent build. With a real Grendel chamber for reliability. Shoots pretty good for a carbine!
- Proper material & finish bolt carrier (8130 carpenter?? or something like that)
- Colt or military contract barrel nut
And I'm more likely to want different gas blocks, handguard/free float setups. So those I build the way I want them. But I'm more of a carbine guy of late. There are probably bench types who would have significantly different preferences.
OK, way more than you asked.
Likewise, there are 6061 grades that are comparable to the 7075 spec. There are also advantages & disadvantages to forged vs billet. Grain structure vs dimensional accuracy, etc.
The better billet CNC receivers are made from 6061 comparable in strength to the spec 7075. Certainly approaching the spec, to the point that you don't hear of billet receivers failing in duty. (There have been some failures from people force fitting parts with excessive force. This is strictly due to tighter tolerances on the billet)
Regarding strength of forgings, you have to also account for the fact that the billet material used in AR receivers is forged to make it a billet. so the only advantage the forged receiver has besides the material is any additional strength in the grain from the forging process, etc. It's not like the billet is "butter soft", or cast.
Realistically, Sundevil or better billet lower receivers have given excellent service. I use them on bench guns. For "hard use" guns (or at least those I would like to have hard use capable), I use a top tier mil-spec forged lower receiver. Not exotic, just a known quantity, for sure, mil-spec receiver (LMT, DD, Etc). Upper receivers it's a bit more difficult to find a "for sure" mil-spec in stripped form. After looking at many options for upper receivers, I came back to AA's deal. It's as good as any non-exotic, made from a quality forging, and excellent fit/finish.
There are volumes of debates on receiver material / mfg on other forums. I lean toward trusting some of the armorers with relatively high volume experience in Iraq on one of those forums. Their conclusion- most people worry way to much about lowers. And often spend too much on exotic lowers. Then go and put substandard components in far more critical roles (bolts, barrels, etc) Which do fail, make bigger difference, etc.
My learning from all this is that I used to build lowers and buy uppers. I now do the opposite. I can get a very good mil-spec lower assembled for not much more than I can build one. The uppers, I build with parts that I know the mfg & provenance, using as much "for-sure" milspec as I can.
I want:
- forged 7075 extension/buffer tube, mil-spec threads & dimensions
- Mil-spec lower receiver
- The best trigger group of the best mfg I can get. I'd consider Colt, LMT, or DD as the only standard trigger groups I'd use. DD can be had for the same as generics. There are other std triggers that are probably OK as well, but I go with known mfgs. I don't have as much experience with high end triggers, so won't comment on them.
Don't think there is a difference in trigger components? There are some pretty good side by side comparisons with Colt, LMT, DD, and then the generics. They are not the same! Nearly all vary, some are noticeably better than others in fit/finish.
I found LMT complete lowers provide the above at a reasonable cost. Not much more than I could build one for. DD used to, but they no longer sell assembled lowers. But would also use them or a Sabre one if available. Or one from a Colt 6920, etc. With the LMT you can also upgrade to a very good two stage for much lower cost than adding the same separately.
On uppers, most of my focus is on the barrel & bolt carrier
- specific barrels depending on caliber/usage. 4150 cold hammer forged if in 5.56 carbine. There are less hard duty options for Grendel, and more target options. So for my Grendel carbine I went with an SS M4 profile minus the M203 cuts on my most recent build. With a real Grendel chamber for reliability. Shoots pretty good for a carbine!
- Proper material & finish bolt carrier (8130 carpenter?? or something like that)
- Colt or military contract barrel nut
And I'm more likely to want different gas blocks, handguard/free float setups. So those I build the way I want them. But I'm more of a carbine guy of late. There are probably bench types who would have significantly different preferences.
OK, way more than you asked.