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AR-15 Gunsmithing for the novice: installing a barrel: part 3.

Think putting on a flash suppressor just needs a good heave with a wrench? It's a bit more complicated.

At this point all barrels have been installed. Now is a good place to insert some information concerning installing flash suppressors or other muzzle attachments.

Believe it or not, but there is a right and a wrong way to install muzzle attachments. Just as with other AR-15 parts, the market is flooded with options for flash suppressors and muzzle brakes.

Since they all attach similarly, I will just use the standard A-2 flash suppressor as an example in this article. The A-2 unit needs to be indexed so that the closed portion is on the bottom.

Simply screwing it onto the barrel will not likely allow it to index in the right position. There are two common methods to align the flash suppressor. The first is to use an item called a peel washer. This is nothing more than a stack of very thin washers that are lightly glued together.

They are installed between the flash suppressor and the shoulder on the barrel. Just peel off however many washers it takes to allow the unit to index correctly when tightened.

The other method is to use a crush washer. Crush washers are cone-shaped spacers that install behind the flash suppressor. When you tighten down the suppressor, the crush washer flattens out and allows you to turn the suppressor into alignment. The shape of the washer allows it to deform, yet still remain tight.

Crush washers are rather expensive compared to regular washers, at about a dollar each, but they work great. They should only be used one time, since once flattened, they will not return to their original shape.

One of the biggest mistakes novice AR gunsmiths make is to overtighten the flash suppressor or not use the correct washers. If the unit comes up a half turn short of alignment, they think that forcing it the rest of the way will solve their problem.

This is a good way to ruin your accuracy. Let me give you a good example of how this taken to extremes can ruin your accuracy potential. A few years ago, I built an AR-10 (a 7.62 NATO/308 Win. version of the AR rifle format) from a bargain-priced parts kit offered by a FAN advertiser.

The parts kit was priced incredibly low and I wondered how they could offer a decent product at this low price. To keep cost as low as possible, the kit seller apparently cut every corner it could on the parts kit.

The standard flash suppressor for an AR-10 is larger and much more expensive than the smaller AR-15 version. The AR-15 version is threaded l/2"-28 tpi and the AR-10 version is threaded 5/8"-24tpi.

On a barrel with a 30 cal. bore, there is very little barrel wall left if you thread the end l/2"-28 tpi. In fact, the wall thickness under 1/2" flash suppressor threads would only be about .070", which isn't very strong.

It appeared that to save a few bucks on flash suppressors, the kit seller decided to use the less expensive and smaller AR-15 flash suppressor. If that wasn't bad enough, the flash suppressor that was used was poorly machined and wobbled slightly as it was screwed on, indicating unsquared threading.

Since it wasn't square when it contacted the barrel shoulder barrel and was tightened very tight by the factory, it caused the very end of the barrel to bend off slightly to one side.

While this may not seem like an issue to the inexperienced gunsmith, it caused the gun to shoot very poorly. Groups with all types of ammo were in the 6- to 8-inch range at 100 yards. It took me a while to figure out why this gun shot so poorly, but eventually I found the flash suppressor problem.

I cut off the 1/2" threads and rethreaded the muzzle to the correct size of 5/8"-24tpi. I threw away the poorly-made AR-15 flash suppressor and made a new muzzle brake of my own design on my lathe. When I did my barrel work I made sure everything was aligned and square.

When I took my reworked gun to the range for testing I found that now the gun shot groups in the 1- to 2-inch range. This single corrective action solved the accuracy problems that came from cutting corners to save a few dollars.

Overly tight and crooked muzzle attachments can ruin accuracy. While this is an extreme example, it shows how your muzzle attachments are installed can make a big difference on how your gun shoots.

Only use quality flash suppressors (not the $5 kind found in a parts bin at a gun show) and use the correct washers and torque when installing them. They only have to be tight enough that they won't come loose under use.

If you are concerned about them coming loose, use some thread locker like Loctite #242 or #271 rather than tightening them down excessively.

Now that the barrels have all been installed on the same receivers, you may wonder how they shot. I have to admit I was surprised at the results.

All upper receivers and barrels were mated to the same Stag Arms lower receiver assembly. The trigger was lightly tuned to give a pull weight of about 4 pounds.

The stock on the lower was a Luth-AR Modular Buttstock Assembly. This is a stock that features an adjustable cheekpiece and is also adjustable for length of pull. This is a nice stock for a target gun, since it can be adjusted to suit the individual shooter.

It has a futuristic appearance and is very comfortable in use. Suggested retail price is $140, but typically street prices are much lower. For those wanting more info on this stock go to the Luth-AR website (

For maximum accuracy I used a CTK AR-15 rifle rest to shoot all 100-yard groups. Since my eyes aren't what they were when I was young I used a scope on all the uppers for testing.

I prefer budget priced optics for my projects because I live on a disability income and do not have big bucks for high dollar scopes like the more affluent gun writers.

For budget-priced optics, I turn to FAN advertiser CDNN Sports. For this project I chose the Target Sports 4-16x40 tactical scope (#TAR202). This budget-friendly scope is priced at only $70. Granted, it doesn't perform like a $500 Leupold, but for poor folks like me it is fine.

It was inexpensive, worked very well, and allowed me to shoot some pretty decent groups: what more could I ask for?

Let's start with the lightweight 20-inch GI format used barrel that I paid a whopping $15 for. I believe this barrel must have been on a parade rifle because the exterior was worn so bad you couldn't even read the barrel makings anymore. I had very low expectations for this barrel.

To my utter amazement, this barrel shot great with some brands of ammo. The best groups shot with this barreled upper were unbelievably shot with a $5 box of Wolf Russian 55-grain FMJ ammo. My five-round groups measured a very tight 1.12 inches, with four rounds even tighter at .625".

The next best group was shot with Black Hills Ammunition 60-grain V-Max load at 1.1 inches. Black Hills 69-grain Match King loads were only slightly larger at 1.2 inches. The worst groups were shot with Remington's 50-Grain Accu-Tip at 2.32 inches.

If I hadn't shot it myself and seen it with my own eyes I would not have believed it. I was expecting 6-inch groups with this old worn finish barrel and what I got was new barrel performance.

I removed the Target Sports scope from the GI upper and installed it on my Stag Arms heavy barrel upper. The best 100 yard five shot group was obtained with the Black Hills 69-grain Match King load. This load printed a center to center group of just .82". This was closely followed by the budget priced Wolf 55-grain FMJ load at .950". A lot of people look down on this budget priced Russian ammo but it has always shot well in my AR-15s.

The Black Hills 75-grain HP load (not tried in the GI upper) turned in a respectable group of 1.13 inches. The Stag barrel shot the Remington 50-grain Accu-Tip load reasonably well at 1.1 inches. The worst groups were fired with Remington's 55-grain FMJ economy loads at 2.7 inches.

Last to be tested was the upper that featured the $440 Shilen match grade barrel. Due to its high cost I had high expectations for this barrel. While it did shoot well, it was only about 25% better than the Stag Arms barrel.

At two to three times the cost of the Stag barrel, I wanted some pretty impressive groups. When it comes to precision barrels, the last 10% of performance takes 90% of the cost. This old saying proved itself here.

The best group fired out of the Shilen match barrel was with Black Hills 75-grain Match Hollow point loads at .71". Next up was the Black Hills 69-grain Match King load at .82". The Black Hills 60-grain V-Max load turned in a .97" group. This barrel really likes the Black Hills match ammo.

The budget-priced Wolf 55-grain FMJ loadings again surprised me with a 1.35-inch group. The worst group was fired with the Remington 50-grain Accu-Tip loads at 2.5 inches.

I have been building and shooting AR-15 rifles for over 40 years and am still surprised on occasion. My experience told me that the $15 barrel would be a poor performer, but when tested, it proved me wrong. That is part of the fun of gunsmithing AR-15 rifles. Many times you are pleasantly surprised at how well an AR-15 can perform. I hope this article prompts novice AR owners to take up hobby gunsmithing. If having an enjoyable hobby that can save you money sounds interesting to you, then why not give gunsmithing a try?



Brownells--200 S. Front St., Dept. FAN, Montezuma, IA 50171, 800-741-0015,

CDNN Sports--P.O. Box 6514, Dept. FAN, Abilene, TX 79608, 800-588-9500,

Stag Arms--515 John Downey Dr., Dept. FAN, New Britain, CT 06051, 860-229-9994,

Luth-AR--3322 12th St. SE, Dept. FAN, St. Cloud, MN 56304,

Caption: Knowing how to change an AR barrel makes it easy to build a variety of uppers for different purposes. You can build uppers for other calibers, as well.

Caption: Flash suppressors, or other muzzle attachments, are typically installed with stacks of flat washers. Some, like the A-2 style, must be indexed in a certain position.

Caption: A crush washer behind the flash suppressor will allow it to index correctly and allow for proper torque when indexed correctly. It's a one-use item.

Caption: All barrels are installed on identical upper receivers and identical bolt carrier assemblies utilized. All that needs to be done now is to see how well they shoot.

Caption: The Stag Arms lower assembly was fitted with a LuthAR Modular Buttstock Assembly. It features an adjustable cheek rest and also adjustable for pull length.

Caption: Matthews installed a Target Sports 4-14x40 Tactical scope on each upper receiver assembly. This budget-priced scope worked very well despite its low $70 price.

Caption: The well-worn $15, 20-inch GI barrel performed beyond all expectations. The best group was fired with economy priced Russian Wolf brand 55-grain FMJ ammo.

Caption: The Stag Arms heavy barrel was very accurate despite the author's poor marksmanship. Black Hills 69-grain Match King loads produced a nice .82" group.

Caption: Not unexpectedly the Shilen Match Barrel fired the tightest groups, though Matthews says the high cost yielded only the last few percent of performance.
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Author:Matthews, Steven
Publication:Firearms News
Date:Jul 1, 2017
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