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AR-10 Build - Copied from Biopar.com
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Old 09-27-2013, 01:24 PM
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Default AR-10 Build - Copied from Biopar.com

I was going to make this part of the AR-15 thread, but I decided it should have it's own. Among the 'things' I have learned with these projects is that unless you REALLY want something bigger than the AR-15 platform can offer, DON'T EVEN THINK about an AR-10. Everything about them is twice as expensive and twice as difficult to find. It's genuinely ridiculous.

You know I milled the receiver from one of Tactical Machine's "80%" blanks. I then started looking for parts. The lower kit is identical - IDENTICAL - to the AR-15 lower kit, but it costs $15 more. When I went to get a butt-stock for it, the one I wanted was "out of stock" everywhere 'on the planet' OR it was twice the price of Midway. I settled for a REALLY UGLY adjustable one.

Paid a ridiculous price for an "assembled" upper. That's a real stretch of the imagination to call an upper with NO BOLT CARRIER GROUP "assembled". I paid $125 for the bolt CARRIER ALONE - no bolt. Everyone is "out of stock" of AR-10 bolts unless you want to pay obscene prices. So I'm waiting for one to come "in stock" so I can only pay a ridiculously stupid price for it instead of an obscene price for it.

I think you can see that I am not particularly 'happy' about the prices associated with the AR-10.

I was planning on chambering the rifle in "8-08". The .308 Win necked up to 8mm. The primary reason being that I have many 8mm milsurp take-off barrels in hand from which I could make an AR-10 barrel. However, when I got to thinking about it, it occurred to me that the 8x57 cartridge MIGHT fit in the AR-10 magazine. If it did, I could simply rethread the milsurp barrel and be ready to go. I checked the max overall length of of the cartridge for the AR-10 as dictated by the magazine size, (2.8"), and found that the 8x57 would fit and "work" even with a 195-grain Hornady loaded. Now I just needed to determine if a milsurp barrel had enough 'meat' on it to allow me to rethread for the AR-10 barrel extension (hereafter "BE"). (Cost of AR-15 barrel extension - $20. Cost of AR-10 barrel extension - $44.) After some measuring and 'cyphering', I decided that it was close enough to give it a whirl and see what it looked like 'in the hand'.

I start with a "large ring" Mauser barrel. (The "small ring" Turk '38 bbls won't work.) Here's a picture of the one I was going to use, chucked in the lathe.



And


(I know it's VERY ugly, but I'll come back to that issue later. Remind me if I forget.) I want you to note specific 'parts' to the stub sticking out of the lathe's chuck:

1) On the breech of the barrel there is a tiny bit of barrel diameter that isn't threaded. That is the diameter of the root of the threads. It is 0.980" in diameter.
2) The threads are right at 1.110" in diameter. That means that the threads are about 0.060" deep.
3) There is a 'shoulder' muzzleward of the threads. It is 1.110" in diameter.
4) The area muzzleward from the shoulder is 0.980" in diameter.

The ID of the Barrel Extension (BE), was 0.930". To the best of my ability to measure them, the BE threads were 0.050" deep. That would mean a MAX OD of the barrel stem of 1.030" to fit the BE. That seems a little too large to consider for the "root" diameter - 0.980" - of the milsurp barrel. Small by 0.050". However, male threads don't extend to the absolute root of the female threads, so I thought that MAYBE the combination of the threaded part of the milsurp barrel, plus the FULL contact of the shoulder of the milsurp barrel, plus at least 'some' of the rest of the barrel, would provide enough 'grab' to reasonably fit the milsurp barrel to the BE. And that's why you see the barrel chucked in the lathe.

I 'pared' everything down to the 1.03" dimension suggested by the measurements on the BE. Here's what that looked like.


As you can see, that got down quite a ways on the threads and provide for what would be at least 4 threads worth on the shoulder. I was hoping that would be 'enough', but knew I would get at least a little bit of 'bite' on the barrel body ahead of the shoulder.

I cut until I was just cutting the top of the threads with the "full form" shoulder on the threading insert and then tried the BE. The barrel was too large. Great! I continued cutting until the BE would just screw on with hand pressure. Here's what the barrel looked like:


As you can see, there's plenty of bite from one end of the threads to the other. This will definitely "work". Here are a couple of pictures with the BE attached, AND a picture of the barrel on the AR-10 receiver.







I am not tightening anything down until I can get a bolt and make sure the headspace is correct. The BE stops abruptly where it should, but I'm not sure that's where it should be in order to put the barrel breech against the face of the bolt. It seems a little too far off right now. I can't really do anything until I have a bolt.

It's a ugly beast no doubt. The barrel is the proverbial "sewer pipe". That's just fine by me. It is my intent to show that "sewer pipes", as long as they don't have mangled muzzles, and aren't bent, can shoot JUST AS GOOD as $500 dollar Lilja barrels. (Or whomever, I'm not picking on Lilja.) This barrel, after cutting off about 4" from the muzzle, is now almost exactly 24" long. I will 'clean it up', true up the muzzle, and have full expectations that it will shoot as well as I can aim it.

More when I get the dang bolt.

Paul
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Last edited by gitano; 10-24-2013 at 04:34 PM..
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