How to beat a $2,000 upper with a $300 Bear Creek (and $200,000 in machining equipment and a $100,000 metrology lab)

[RR Hunter]

Work on the Lower began in earnest.

The Hera CQR was split so that I could document the internal structure. Germans really don't do polymers as well as they do metals, but the design philosophy and engineering was okay.

I measured the mil spec detent springs I ordered for a hollow set screw, so that it did not trap grit and oils in the receiver. I tapped the hole, clipped the spring a bit shorter, and inserted the 14-40 screw.

Next was to deal with the atrocious control fitment on most AR based rifles. The gap between the selector and the receiver was far too large for my taste. I whipped up a couple 3/8 x .062" bronze spring washers to go behind the selectors. That was a massive improvement in feel.

I also ordered stainless pan head screws with stainless tooth washers because I wanted to spread the engagement over a larger surface area inside of the polymer stock.

The M5 lowers are already threaded internally for a large nylon tipped set screw to adjust takedown pin pretension, which is a big plus!

 

[RR Hunter]

I am so in for this one.

jUsT aS gUd meets dOn'T bE pOoR and I love it.

Also, what's yer TV for the cat?

This is probably the most pleasant description you could give of me.

Jacob is free. He's a rat Bastard. Poopie, our obese cat not pictured is the baby in our house.

 

[RR Hunter]

Fitting the CQR to the rifle was another hand-fit mountain to climb.

As some of you may know, building an AR-10 platform rifle is nothing like an AR-15. There's really no standard ""mil-spec"" for manufacturers to look at and copy. There are many different generations and changes made by Armalite and DPMS over the years, but I'm going to avoid getting too deep in that rabbithole for this thread. Just know that we are building a DPMS gen 1 LR-308, Low rail pattern rifle.

So of course, like most AR-10 parts, the CQR wasn't even close to fitting the Aero M5 lower. A lot of material had to be removed. I took my time with a few different die grinding tools and the result was fairly solid feeling. I opted not to polyurethane fill the stock, to keep after my original weight goal.

The BCA bolt retaining pin also had to be ground down to fit. Joy oh joy.

But at last, I got my first glimpse at the finished rifle! The only step left is the accurizing of the upper receiver and final assembly!

 

[Mr. Goodbar]

Following

 

[BEREZKA]

No uodates?

 

[Bagman]

"my entire armory room"

That's bad-ass right there.

 

[edman99]

Watching...

 

[RR Hunter]

Can't believe I didn't finish this thread!!

Actually, I can believe that. I am lazy.

Spoiler alert for those who don't want to wait:

.266"

 

[RR Hunter]

Trigger warning for zoomers: The following posts contain images and descriptions of shimming barrel nuts, "bedding" barrel extensions, lapping receivers, honing BCG rails, lapping bolt faces, etc.. If any of this sounds like snake oil to you, it might be. Calm down, it will be okay.



After finishing the lower and took it to the range, the factory upper produced groups under 1 MOA! Hooray! We're finished!

Right...?

I mean.. ~.75" groups have to be good enough for anyone....

Right??


Right. So now the most painstaking process begins... Accurizing of the $300 Bear Creek Arsenal upper receiver.

 

[RR Hunter]

For the first time in a while, the "armory room" is clean...

Let's ruin that!

The first part of the process is of course to mount the upper in our 1913 rail fixture and begin disassembly.

Besides BCA hiring Hulk Hogan to install the barrel nut, everything came apart with relative ease.

The first order of business is lapping the receiver.

This involves using a brake master cylinder adjustable honing stone set to debur and remove all of the tooling marks inside of the upper. Be careful not to remove all of the hardcoat anodizing or your BCG will become very sluggish from galling.

The second step is using a receiver lap and a few .002" shims to true the barrel extension socket to the receiver. You don't need to go all the way, but sadly I did have to take a great deal out of this one...