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Budget built big bore AR-10 part 2: here's a build that won't take much time, especially if you've built ARs in the past. And the savings over a complete AR-10 are significant.

Trigger and Disconnector

The installation of these parts is eased with the help of a simple-to-make installation aid. This little tool is nothing more than a slave pin made out of a 3/8" long piece of 5/32" (.156") rod. This little pin will hold the disconnector in its proper place while under spring tension as you install the trigger into the receiver.

Place the disconnector spring into its pocket in the trigger with the wide end of the spring in the pocket bottom. Place the disconnector into the trigger and align the holes, followed by sliding the short slave pin into place to hold the assembly together.

Now install the trigger spring over the trigger. The square end fits right under the front of the trigger and the two legs face forward. Slide this assembly down into the receiver, align the holes, and slide in the trigger pin. (Note to novice builders, the hammer and trigger pins are the same.) As the trigger pin is being pressed in, the slave pin will slide out the other side as long as you keep things aligned.

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Safety Lever

Place the safety lever into the receiver with the lever portion on the left side of the receiver. The lever will be retained later by a spring-loaded detent. The lever must be installed now because on some (but not all) AR receivers, there isn't enough clearance to install the safety after the hammer is installed.

Hammer

Install the hammer spring onto the hammer. With the hammer oriented upright and the spring legs facing rearward, slide the hammer down into the receiver. Push down hard to overcome the tension of the hammer and trigger springs. Once the holes in the receiver and hammer align, install the hammer pin.

Be sure the legs of the hammer spring extend back over the trigger pin as that is what retains that pin. The hammer pin is retained by an internal spring in the hammer.

Rear Takedown Pin and Pistol Grip

The safety lever and rear takedown pin are retained by springs and detents that are held in place by the pistol grip. Install the rear takedown pin into its hole with the head on the right side of the receiver. Push the safety lever back fully into place if it has moved out of position.

Place the larger safety lever detent into its hole under the safety lever. Place the smaller takedown detent into its hole. Place the takedown detent spring into its hole in the bottom of the receiver. Place the safety lever detent spring into its hole in the pistol grip.

Slide the grip onto the receiver so that it tensions the springs. Once the grip is all the way on, install the grip screw to retain the grip. Be careful when sliding the grip into final location, as it is very easy to kink the springs, as they are being tensioned.

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Buffer Tube and Buttstock

Place the buffer detent and its spring into its hole in the rear of the receiver. Screw the buffer tube onto the receiver and push down the buffer detent before the tube is screwed on all the way. Once the tube is fully forward, the buffer detent can be released and it will be retained by the front of the buffer tube.

Use a wrench on the rear of the tube to tighten down the buffer tube. Be careful not to exert too much force when tightening the tube. It is made from aluminum and can be easily damaged if over-tightened.

I usually put a drop of blue Loctite thread locker on the tube threads to keep it from ever loosening. Now you can slide the buttstock over the buffer tube and secure it with a single screw through the buttplate.

Be sure to remember to drop the buffer tube spacer down into the stock (oriented correctly) before you install it. This spacer is required since the buffer tube is made for the old A1 type stocks. The newer A2 stocks are longer and the spacer is used to fill, in the extra space. Finally, lightly lubricate the buffer and its spring and install it in the buffer tube.

At this point the fire control group should be checked for proper operation. Cock the hammer to be sure the trigger engages it and holds it back, pull the trigger to verify that it releases the hammer (hold the hammer when doing this, allowing the hammer to fly forward without the upper installed could damage the receiver).

Check that the safety and disconnector work properly. Note that on AR-type firearms the safety can only be applied when the hammer is cocked.

If everything checks out, the upper can be assembled to the lower. Once it's installed; cycle the action and verify that everything is working right and there is no binding when the action cycles. On my project, everything worked right and there was no need to fine tune or hand fit anything.

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Sight Selection

Since this firearm features a 1913 rail on the upper receiver, the front gas block sight options are almost unlimited. There are literally hundreds of sight options for the AR family. Since I was doing this as a budget-priced project, I went with budget-priced optics. I, like a lot of other "financially challenged" SGN readers, don't have hundreds to spend on big-buck scopes.

I know there are folks out there who think you have to spend big bucks on high-dollar optics especially since that's all you ever see reviewed in magazine articles and that's fine for affluent readers.

I will be the first to say that budget-priced import optics don't perform like high-priced premiums optics like Leupold, Redfield, Nikon or others. On my budget its low cost optics or no optics at all!

The place I turn to for most of my budget-priced scope needs is SGN advertiser CDNN Sports. Their catalog and website is filled with budget-friendly optics. I ordered one of their products that I have used on two other projects with good results, the Target Sports 10x42 Tactical scope (#TAR31).

This fixed 10X scope features a 30mm tube and is priced at $60, which includes a set of high-rise rings that are just the right height for an AR project. In my experience, this budget friendly scope has performed well beyond its low price. I know there are "scope snobs" that will ridicule my selection, but I have this scope on a target AR-15 and that combination will shoot 1/4-3/8" groups. This kind of performance is way beyond what I can shoot with open sights, so if this scope allows me to shoot this well, then it's good enough for me!

Test Firing

Keeping with the budget theme, I rounded up some budget-priced .308 Win./7.62 NATO ammo. I used Winchester's white box USA FMJ ammo and some Venezuelan NATO-spec military surplus 147-grain ammo for which I paid $3 a box back about 10 years ago, so it is certainly budget priced considering today's .308 prices. I added some inexpensive handloads that I loaded with match bullets but no other match components.

Accuracy of all of them seemed to be about the same, about 1 1/2-2 inches at 100 yards, which is pretty much the norm for any non-tuned AR. I'm sure that with specially selected loads, a better trigger pull, better optics and most importantly a better shooter, groups could be cut in half. I always hate to report accuracy in my articles since. I can't hit the broad side of a barn. It's unfair to report the accuracy of a firearm with a shooter who couldn't shoot much better than 2-inch groups even with the world's most accurate gun.

The gun was pretty tight at the beginning of the test and I' had a few short strokes, but as the test continued, the action loosened up and functioning gradually made it to 100%. Rounds that wouldn't cycle the action reliably (the Venezuelan NATO) at the beginning of the test functioned fine once the gun was fired some and worn in.

Final Thoughts

For an AR-10 this project was a real bargain. It shot well, was reliable, and was easy to build. While you can spend a lot more for an AR-10, I don't think you'll get much more value for your money. If this sounds like your kind of project why not give it a try!

Epilogue

That pretty much sums up the build process on this project but sometimes there is "more to the story." On my next shooting session with this project a few issues came to light. First, I noticed that some brands of ammo chambered extremely tightly.

I also noticed that the gas block/sight base had rotated slightly out of position. I assumed that the lock screws had come loose and allowed the base to move so I grabbed the base and tried to move it. Sure enough it turned.

Unfortunately the block hadn't really turned, the whole barrel had turned! This meant a return to the shop, because a turning barrel on an AR project means major problems. After I removed the gas block and handguards I could see that the barrel was unscrewing from the barrel extension.

In fact it was so loose I could screw it out by hand and completely removed it from the receiver while the extension remained secured to the receiver. Apparently Blackthorn's barrel supplier hadn't torqued the barrels and extensions tight enough. This was not good!

I contacted Blackthorne and they immediately sent me a complete new upper with barrel and bolt assembly. They said they were very sorry and would do their best to correct the situation since their products were warranted.

The new upper assembly arrived a couple days later. Unfortunately it also has some issues. First, the sight base/gas block was noticeably out of position. It was about 10[degrees] off vertical. Fortunately, this was easily corrected by loosening the lock screws and repositioning the block.

While inspecting the bolt I couldn't help but notice that the front edge of the extractor had been very crudely ground flat with a hand grinder rather than being contoured like the bolt face.

I replaced the crudely ground extractor with the good one from the original bolt. The ejector was also very crudely formed. It had very sharp edges on its sides and a sharp bump protruding from the center.

My original ejector was also poorly shaped this way, and all fired cases had a big gouge scraped on the base of the cartridge. This also created a fair amount of brass shavings. To correct this problem, I removed the ejector and radiused the edges and removed the sharp spot in the center. Once these little issues were corrected, I headed for the range.

At the range the gun would chamber and fire Winchester USA and Venezuelan NATO spec ammo but it did so rather sluggishly. Unfortunately, when I went to use Remington UMC, Federal, and Spanish Santa Barbara NATO spec ammo the rounds were hammered partially and tightly into the chamber, which bound everything up.

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The rounds were so tightly wedged in the chamber I had to strike the butt against the shooting bench while pulling as hard as I could on the charging handle to eject the jammed rounds. This meant a return trip to the shop to see what was wrong.

Examination revealed no problems with the bolt or carrier, and the chamber was free of any obstructions. At this point I suspected that the barrel was not headspaced correctly and got out my headspace gauges (available from Brownells at very reasonable prices) to do a headspace check.

Sure enough, when I tried to close the stripped bolt on my chambered .308 Clymer 1.630" Go gage it would not close. This indicated insufficient-headspace. This is a major problem for the average person since the tools and knowledge needed to correct this problem are usually beyond their means.

Most people would have to return the upper receiver assembly to Blackthorn for yet another replacement. I have the skills and tools to correct this problem, so it was easier to fix it myself rather than send it back.

Since this article isn't a headspace tutorial I will just say that I had to make a .007" headspace adjustment by deepening the chamber with a .308 Win./7.62 chambering reamer that was obtained from Brownells.

Once this adjustment was made, the 1.630" Go gauge was used to again check for minimum headspace. This time the bolt would close correctly. A 1.634" No gage was used to check for excessive headspace. The bolt would not close on the 1.634" gauge. This indicated the head space was now within specifications.

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These barrels were supposed to be checked for correct headspace at manufacture. I use industry specification tools and my measurements indicated the headspace was about .007" too tight. I do not know how a barrel maker could pass a barrel this far out of spec considering that they are being checked with the same SAAMI specification tools as I use to measure headspace.

Somewhere along the way something was not right when the barrel was made and mated with a bolt assembly. Either the bolt, barrel, barrel extension or headspace measuring tools had to be out of spec to allow this barrel to pass inspection.

Once this problem was corrected I returned to the range and now the gun operated correctly and reliably.

These problems raise the question of whether the Blackthorne kit was a good buy or not. As I said at the beginning, I was unfamiliar with Blackthorne when I started this article. I did some internet research on Blackthorne and did find that there have been many Blackthorn quality issues reported on many of the AR forums.

I also saw reports from Blackthorne customers who were completely happy with what they had bought. General opinion on the forums seems to be that Blackthorn's quality control is pretty erratic.

Based on price alone, the kit is a real bargain. Overall material quality was very good. The problems I encountered were correctable but you don't want to have to repair new products. The whole issue boils down to quality control.

Every manufactured product has substandard parts and procedures that have to be weeded out during the manufacturing process. The Blackthorne kit is a decent kit but their quality control leaves something to be desired.

While the kit is a bargain at its low price Blackthorne would be better served by putting $50-$100 more quality control in each kit and raising the price to pay for it.

Both barrel problems should have never made it out of the factory. If Blackthorne can get their barrel supplier to correct the problems, then this kit is going to be the "bargain of the day" in the AR-10 kit world. So do I recommend it? Yes, but be aware that you may have to do some gunsmithing to get it up and running. I hope by the time this article goes to press that Blackthorne has their issues resolved.

Once the problems were worked out I was very pleased with the project, especially at its low project cost. Blackthorne has the opportunity to put a great product on the AR market if they can resolve these problems.

RELATED ARTICLE: BUDGET BUILT BIG BORE AR-10 ARTICLE RESOURCES

Blackthorne Products LLC, Box 2441, Dept. SGN, Inver Grove, MN, 55076, 952-232-5832, www.BlackthorneProducts.com

CDNN Sports, Box 6514, Dept. SGN, Abilene, TX, 79608, 800-588-9500, www.cdnnsports.com

Brownells, 200 S. Front St, Dept. SGN, Montezuma, IA, 50171, 641-623-5401, www.brownells.com

RELATED ARTICLE: SGN GUNSMITHING PROJECTS

Want to read even more about home gun building? Get Shotgun News Gunsmithing Projects, a 448-page compendium of a decade's worth of gunsmithing stories from Reid Coffield, Steven Matthews and other SGN writers. Whether the project is restoring a double-barrel or building a semi-auto Bren gun, you can read about the skills, tools and materials you'll need to make it a gun you'll be proud of!

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Author:Matthews, Steven
Publication:Shotgun News
Date:Aug 20, 2012
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