12-03-2018, 11:33 PM
When we started cutting our own lowers (based on forgings) I really geeked out on all of this. Eventually we settled on 7075-T6 and I've forgotten more about the alloys than I remember. I do recall that the 7075-T6 was a pretty good fit for our lowers and we've been very happy with our choice (there are different tempers to 7075, I'm not sure what designation the majority of forgings are - you could probably educate me!).
It goes past materials though, as FRB6.5 mentioned the final machining is what really separates one lower from the next, for good or bad. Again, when we first got into this, we bought every stripped lower that we could find. From the $24 budget special to the $249 billet race lowers, we had a sample of them all. We built and tore down every lower more times than I care to remember using every LPK we could get our hands on (again from the dollar store special to the fully machined ultra premium) and took copious notes along the way. What worked, what didn't, where did we run into problems, what was too tight, what was too loose, what problems did we run into along the way, we checked various magazines (this was pre-PMAG) and uppers, tried every trigger would could get our hands on, etc, etc... We then sat down w/the current mil-spec schematics and spec'd them all out. In the end, we compiled all this data to arrive at exactly how we wanted to build our own. In the end we built them as close to the initial design parameters as we could and did everything that we could to eliminate tolerance stacking (despite the added cost in doing so) and increase strength in the critical spots. What we ended up with is lowers that are true to spec and absolutely dead on as far as holes being in the right place, the deck being level, and the buffer tube being square to the rest of the gun. Again, as FRB6.5 mentioned, the price we ended up paying in the end for sticking true to tolerances is that oversized mags (yep, a lot of PMAGs are out of spec) don't always drop free. If that's a deal breaker, it's nothing that a file and some Alumahide won't fix.
That said, lowers have gotten a lot better over the years. Even the ultra cheap lowers are more in spec today than they were even 10 years ago and you run into fewer and fewer problems now than you once did. I'm still happy that we spent the extra time and expense to get the lowers up to the level of quality that we demand, even if PMAGs don't always drop free and the costs were a little higher.
Another thing to consider is that the lower is "the gun" and holds your serial number. It's the single part that isn't easily and readily swapped out after placing an order at your favorite online retailer. For that reason alone, especially considering the political climate when it comes to EBRs, I tend to stick with higher quality lowers. As you mentioned however, I've seen crappy polymer based lowers produce some pretty nice groups. Grab what you want and go shoot!
It goes past materials though, as FRB6.5 mentioned the final machining is what really separates one lower from the next, for good or bad. Again, when we first got into this, we bought every stripped lower that we could find. From the $24 budget special to the $249 billet race lowers, we had a sample of them all. We built and tore down every lower more times than I care to remember using every LPK we could get our hands on (again from the dollar store special to the fully machined ultra premium) and took copious notes along the way. What worked, what didn't, where did we run into problems, what was too tight, what was too loose, what problems did we run into along the way, we checked various magazines (this was pre-PMAG) and uppers, tried every trigger would could get our hands on, etc, etc... We then sat down w/the current mil-spec schematics and spec'd them all out. In the end, we compiled all this data to arrive at exactly how we wanted to build our own. In the end we built them as close to the initial design parameters as we could and did everything that we could to eliminate tolerance stacking (despite the added cost in doing so) and increase strength in the critical spots. What we ended up with is lowers that are true to spec and absolutely dead on as far as holes being in the right place, the deck being level, and the buffer tube being square to the rest of the gun. Again, as FRB6.5 mentioned, the price we ended up paying in the end for sticking true to tolerances is that oversized mags (yep, a lot of PMAGs are out of spec) don't always drop free. If that's a deal breaker, it's nothing that a file and some Alumahide won't fix.
That said, lowers have gotten a lot better over the years. Even the ultra cheap lowers are more in spec today than they were even 10 years ago and you run into fewer and fewer problems now than you once did. I'm still happy that we spent the extra time and expense to get the lowers up to the level of quality that we demand, even if PMAGs don't always drop free and the costs were a little higher.
Another thing to consider is that the lower is "the gun" and holds your serial number. It's the single part that isn't easily and readily swapped out after placing an order at your favorite online retailer. For that reason alone, especially considering the political climate when it comes to EBRs, I tend to stick with higher quality lowers. As you mentioned however, I've seen crappy polymer based lowers produce some pretty nice groups. Grab what you want and go shoot!