I've done a handful of 80% builds and they all have been 6061. The reason has been because I don'tt feel there is a real world use benefit to the additional strength of 7075, I'm cheap.  and they usually cost more. A friend of mine has a nice looking AR10 lower he doesn't plan to build and offered to sell it to me. It's 7075. I'd like to know if it takes a lot longer to mill a 7075 with a jig and drill press compared to doing one made from 6061.

You will likely not notice it due to the process.  If you had a proper mill, you'd probably notice being able to take bigger bites.

In a mill, you wouldn't notice a difference.  I doubt you would in a drill press either.  


FWIW, if you shop around, you should be able to find 7075 for just as cheap if not cheaper than 6061 as the 7075 is more common, quantity>price.  There are several recent posts about 80%'ers.  Check them out, lots of good info and links.  Ares has theirs on sale now for $60.  As others have mentioned in similar posts, they do require a little clean up work as the finish milling is not perfect, but I've done a few and would certainly buy more.  I also like Coats Carbine.  I prefer billet to forged for asthetics only.  I have a couple of Anderson(forged) and TR Enabling(billet) as well.  All of the 80's I've bought were under $75, the anderson forged were under $50 at the time.  Again, all 7075.  While the difference between 6061 and 7075 may be minimal to neglegible, if you can get the 7075 for the same price, why not.

Not true, 7075-T6 has a UTS and YS of close to double 6061-T6 at normal temps.

Either would function just fine as an AR lower though, but the two alloys are significantly different, especially in their T6 state.  7075 also machines cleaner in my experience, while 6061 can be a touch more gummy.

I agree, 6061 is a bit more gummy. I would much prefer to work with 7075 or 7068 it's a crispier chip and finish.

I meant minimal to neglegible difference "in the application", AR receiver.  I'm sure 6061 would be just fine for an AR receiver, but if the money is the same, even $10 difference, buy the 7075.

Gotcha.  OP would be machining on whatever he buys too, just trying to help him understand the differences.

Thank you very much for the input. I was hesitant to try 7075 because I thought it would take much longer to mill with a drill press due to the hardness. Now I'm looking forward to giving 7075 a try. I just may take up my buddy's offer and snag his AR-10 7075 lower.

I've not milled an 80% upper, but have worked with 6061 and as I racall was always having to clean the cutting tools because it would gum up or gall.  A bit of a pain.  Harder stuff cut much cleaner but didn't take any longer to speak of.  Don't fear 7075

every comment so far as to machinability is spot on.

If you are looking for 7075, look on Ebay for FORTAL.  It is a 7075 variant that machines extremely well, meant for mold making in the real world.

It used to be sold by mousebar, but a new guy took over this source of cutoffs.