https://billet80.com/index.php?route=product/product&path=59_62&product_id=121

Has anyone ever used one of these? What upper do they use? and how reliable are they?

I got the BRS upper receiver.

A KS47 upper would work.

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how reliable is it?

Magic 8 ball says ask again later....like when it's built.
 

I have no doubts it will be fine. I've built many 80's now. Not a single issue with any of them.

I am building one now.

Let me share what I've learned (the hard way).

First of all, the 80% receiver is nicely made, and was easily completed with my Modulus jig.
Here's where it gets tricky: AK mags are fatter than AR mags, and they seat higher up into the upper receiver.

To allow the mag to seat properly, you need to fit the upper and lower receivers together, turn them upside down, and then you can easily see (and mark) where metal needs to be removed (from the upper) to allow the mags to seat properly (by looking inside through the magazine well).
Easy-peazy.

But... (and it's a big butt), after milling away the "just right" amount of metal, the walls of the upper are incredibly thin. Thin like a Somali with cancer.

By good fortune, I also had a DPMS Lo Pro upper, and the walls are thick enough that removing that metal doesn't effect it all. And it's not expensive. And, it doesn't have a FA, which I actually wanted

So, I'll finish it with up with Lo Pro upper, and shoot it that way for awhile. Meanwhile, I'm going to try to TIG some aluminum on the outside of the regular upper to thicken up the areas where metal was milled away.

All because I didn't want to pay $199 for the Billett80.com that is made for the receiver (which still seems like too much money to me).

G.

That upper is almost certainly 7075.  I don't think there's an approved welding procedure for 7075.  Please correct me if I'm wrong.

IIRC you are correct.







 

Relevant to my interests and passing the info.  

From the Variants Forum
Milling out an AR upper to except x39 AK Mags