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Posted: 2/4/2008 7:02:00 PM EDT
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Just getting ready to purchase another fire stick! I have a question on metallury? Dpms uses 6066 t-6 alluminum billet uppers on there ar10 models and 6061 t-6 alluminum lowers. On there ar15 platform they use 7075 t-6 alluminum like most other makers. So why do they use a softer metal for larger calibers? They will not answer my emails. Thank you, I enjoy this sight for those of us who cherish our rights we fought for. Never give up! |
Chances are that they can get by with it, but if you get into the tens of thousands of rounds range, the receiver might get brittle in high stress areas that you can't see, and burst. It probably just made the engineer happy to use the 6061. With fatigue though, and the challenging forces involved with a such a rapid pressure spike there is no real way to know for sure without testing a few guns to failure. |
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I don't know where CSM gets his data, but it does not agree with mine. The fatique strength of 7075 is damn near 50% greater than 6066, and since AR receivers never see a pressure spike of any kind, I really don't understand this talk of bursting. DPMS makes a lot of unconventional upper receivers, and it is likely that a lot of them are made by extrusion. All of the 7000 series aluminums have lousy extrudability, and that is likely why DPMS chooses to use the 6066, as it has fairly good properties in this regard. 7075 is the best choice when manufacturing by the forging and machining route, but other manufacturing methods demand other alloys. |
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I have to agree with Battlerife. While I have not worked with 6066, I have worked a lot with 7075 and 6061 Aluminum. If I have a choice, I will take the 7075 hands down. We make a lot of tooling out of 7075 that is subjected to some harsh conditions and it stands up very well. We have not experienced any cracking problems at all. All of the forgings I have purchased for AR uppers or lowers have been 7075 and they have held up very well, no failures to date, 6061 is softer, gummier than 7075, I'll take my chances with the 7075. Pat |
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7075-T6 was/is the gold standard for structural forged aluminum products for the aerospace industry, at least up through the B777. My understanding was that it replaced 2024/6061 back in the '60s as the baseline aluminum alloy for aerospace applications My limited references don't show 6066 as an alternative, and my guess is that it was a missprint (they really meant 6061), rather than a statement of fact. Another guess would be that anyone using 6061 got a "deal" on some obsolete alloy. I'm sure 6061 is just fine for the AR15 application, given the low structural loads it's subjected to. Aerospace quality castings using A355/A356 alloy would also be completely acceptable--to me, at least given my experience with those producgs. Cheap castings/die castings--no. |
| It is all so confusing. DPMS is not the only make that uses 6061 in both uppers and lowers. But they use 7075 in the 5.56,204 ruger... And then they use 6061 in the larger calibers. POF,STAG,RRA,COLT AND OTHERS USE 7075 FOR ALL CALIBERS. Thank all of you for the help! |
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