On Mon, 8 Apr 2013 21:55:22 -0500, "Terry Coombs"
wrote:

"Ed Huntress" wrote
Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.


--
Ed Huntress


You're wrong Ed , I've melted and cast 7075 in my home foundry . Now what
I can't do is heat-treat and forge it at home . I'm not sure what's
involved with forging , though I'm pretty sure Al is worked cold . Might
have to carry a billet up the road and see what my neighbor can do with his
trip hammer ... Heat-treat requires some expensive precision equipment
though .

Well, you may have gotten lucky, or you may have a casting with
sub-surface porosity and segregation. The closest casting alloy to
7075 is 713.0, and it has less than half as much copper as 7075.

And a fraction of the strength. If they could cast 7075 versus using
713.0, they surely would.

But I hope you got lucky.

--
Ed Huntress