AR-15 Upper Quick Fixes: Match Bolt Carriers

If you want an accurate rifle, don’t leave a lot of front/back bolt play (keep it .003″ but no more than .005″). Factory rifles run .012″ to .015″ play, which is OK if you need to leave room for dirt and grime in a military or field application. However, that amount of play is not ideal for a high-accuracy AR build. A lot of front/back bolt play allows rounds to be hammered into the chamber and actually re-formed in a non-consistent way, as they are loaded into the chamber.

The bolt affects accuracy in an AR-15 more than the carrier group. To get the most accuracy, the bolt and barrel have to be machined so that the headspacing is optimal when the round is chambered and the bolt locked. That is why if one orders a match-grade barrel for an AR-15 either the barrel comes with a bolt, the barrel manufacturer requires you to send in your bolt (prior to machining the barrel you’ve ordered), or the manufacturer requires you to send dimensions from your bolt.

The best accuracy usually comes from the bearing surface of the bullet nearly touching the rifling. Having the bullet jump any significant distance to the rifling tends to negatively affect accuracy. This is true in any rifle, not just the AR-15.

In addition to the above, you will want to keep the chamber, barrel extension, and carrier assembly clean to help insure consistent bolt lock ups critical to accuracy. You will also want to occasionally apply lube directly to bolt rings during shooting sessions.

Carrier key staking is also mentioned in the article. Young Manufacturing does not stake their carrier keys. “There has been a lot of talk about the pros and cons of staking the gas key on the carrier. Here is our opinion and why Young Manufacturing will not stake keys. We have been making carriers since 1991. The US Mil Spec. assembly drawing requires the carrier key to be staked. Contrary to some popular opinions staking does not SEAL the gas key. Staking keeps the screws from backing out Period. If you do not properly torque the screws to 56 inch pounds you will be staking a screw that is loose or one that is over torqued and prone to breakage.” Not sure how I fell about that, for me, a staked key is the only way to go. Something just does not feel right about it not being staked.

REFS:
http://bulletin.accurateshooter.com/2015/05/what-makes-an-ar-accurate-whitley-offers-answers/

Staking the gas key on the AR-15 and M-16 carrier.

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AR-15 Buy vs. Build

There are three options for acquiring and AR-15, it will be up to you to decide which method best suites you. Buy, build, and join the 80% club. In a nutshell buying from a reputable manufacture is the easiest, there are great manufactures that make great weapons. Building will let you get more involved in your rifle, and 80%er will give you the highest level of building most of us can get. If you are only going to own one AR style weapon, buying might be your best option. If you are hands on and will be owning more than one you will want to look at building.

Here are a few larger manufactures if you are looking to buy, this is in no way a complete list.

Colt: From their web site, “Colt’s rifles are the only rifles available to sportsmen, hunters and other shooters that are manufactured in the Colt factory and based on the same military standards and specifications as the United States issue Colt M16 rifle and M4 carbine. Colt customers want the best, and none of Colt’s competitors can match the quality, reliability, accuracy and performance built into every Colt rifle.” To me that statement means if you want what has been battle proven choose Colt. Just remember, battle proven might not be what you are looking for.

DPMS: Provides a very wide range of calibers for the AR’s to include .22, .223, 5.56 NATO, 308, 7.62, 204 Ruger, 243 WIN, 260 REM, 300 AAC Blackout, 338 Federal, 6.5 Creedmore, and 6.8 SPC II. That is a very wide range for one manufacture.

Bushmaster, SIG, Rock River Arms, Bravo Company Manufacturing, and the relatively new to the AR world Springfield Armory are all great choices for manufactured AR’s.

Here are a few pros and cons of both buying and building, we will start with buying:

Pros:

  • Easy: Buying a manufactures rifle that meets your needs is the easiest, quickest way to get into modern sporting rifles. You will be able to find a rifle you want and get it on the range without having to take the time to piece their firearm together.
  • Less Worry: Buying an AR rather than building gives you peace of mind that as long as you follow instructions when using your new firearm, it’s going to work as advertised.
  • Fit and Finish: When building, you have the option of picking components from different manufacturers. However, that assumed flexibility may not always come through, as some components have varying tolerances and dimensions, and may not fit or work properly with all parts. While AR systems generally share interchangeable pieces, you may wind up with parts that just don’t work together. Buying a complete rifle ensures the components fit together properly and work as advertised, taking out the guesswork and potential of making costly mistakes for prospective buyers.

 

Cons:

  • Plain: Buying off the shelf will give you a functioning, ready-to-shoot rifle, but depending on what you choose, you may feel underwhelmed at the features it offers. You can always upgrade parts as you go to give you the custom gun you want, but that costs more money and time, and could potentially wind up being more expensive than if you had built from scratch in the first place. Some manufactures may have proprietary parts that might not be upgradeable.

 

  • Cost: Manufacturers offer endless options in the AR market offering what seems to be an overwhelming amount of options. Building allows users to construct similarly capable weapons where they have complete control over which components and brands they opt for, allowing them to also choose where and what to spend extra on to get the desired result in a time frame that works for you and your wallet.

And now building:

Pros:

  • Make it yours: Building your rifle gives you the features you’re looking for, and you’ll likely be stuck with fewer unnecessary extra parts when you’re done.
  • Experience: One of the best ways to familiarize yourself with your AR is to disassemble and reassemble, learning the intricacies and minutiae of the system. Building an AR gives owners an education in how the rifles are constructed and how they operate, which can come in handy when it comes time to replace parts or help a fellow AR owner in need with quick fixes.
  • Ease of Supplies: The parts, from the barrel to the buffer tube, fire control group to the upper receiver itself, can be shipped directly to you. The only part that requires a FFL is the lower receiver.

Cons:

  • Wallet Creep: It can happen if you’re not clear on what you want, keep opting for add-ons, premium components, or changing your mind mid-build.
  • Tools: As assembling ARs requires some specialized tools to properly get your rifle together, something you’ll need to factor in when pricing your setup. Depending on what you have already you might still need an armorer’s wrench, a set of roll pin punches, a level, a vise and receiver vise blocks, a torque wrench, screwdrivers and more.

For the most adventurous builder there is the 80% lower. An 80% receiver comes partially completed with the trigger/hammer (fire control) recess unmilled, and the selector, trigger pin, and hammer pin holes often need to be drilled out. An 80% lower receiver can be purchased online, shipped, and received by the purchaser without a firearms dealer or FFL. In addition to the above tools you will need access to a drill, preferably a drill press, a router, and a good jig. Once you are done milling it out, it is just like a regular build.

REF:

Vendor Web Sites

https://www.nrablog.com/articles/2016/5/america-s-rifle-to-build-or-buy/

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The Relationship of Barrel Extension Diameter To Accuracy In The AR-15, Part 1

Slop in fitting the barrel extension to the upper receiver can rob your rifle of its potential accuracy. AR-15 barrels don’t screw directly into the receiver. They screw into a barrel extension that slips into the receiver. Since it is a slip fit there is a lot of play. Anyone who has ever re-barreled or watched videos of folks assembling an AR-15 upper will note that up until screwing the barrel nut in place the barrel will wiggle around. Trying to correct the issue by over torqueing can damage the receiver and affect the barrel harmonics. You should apply the recommended torque and try the corrective actions we will discuss below.

This can be fixed a couple ways. You can use green Loctite, the #620 is designed to withstand high temperatures like one would expect near the chamber. The 620 was designed for slip fits where gaps are large. It is thicker than the red Loctite and seems to fill gaps between the barrel extension and the corresponding inside surface of the receiver quite well.

You can purchase some shim stock, start with very thin 0.001″ stainless shim stock. Then with shop scissors cut a shim about ¾” wide and 2 ¼” long. The barrel extension has about one inch of bearing length, not including the flange and cutting the shim stock a little on the narrow side gives you leeway to keep it centered and not extending out from either the front or back. Wrap the shim around the extension and attempt a trial fitting, first without Loctite, to see if the barrel will go into the receiver with the shim stock in place. If I still have a lot of slop I cut another replacement piece of stock a little longer. If the fit is too tight to go in place you can gradually trim the length until everything goes tightly in place. Then as above apply green Loctite #620 after making sure everything is clean and degreased.

The downside to both these methods is removal, Loctite is a semi-permanent method. You can try to remove the barrel with heat, a block of wood and a hammer but risk severely damaging your receiver, barrel or both.

The article that this paper is based on is from American Gunsmith Magazine, dated March 2013. Almost exactly 5 years ago and there is much controversy on this subject. As with all things AR, it breaks down to personal preference. Do you want a rifle to go out and plink with, or be super accurate at over 500 yards? If the later, you might want to consider shimming it up, if not, standard build methods will be just fine for you.

REFS:

Various firearms forums

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Iron Sights and Optics

Now a days there are many different types of iron sights for your AR 15 rifle but for this paper we will focus on two, the A1 and A2 sights. The A1 type’s rear sight only supports windage (right-left) adjustments, and the A2’s rear sight has both windage and elevation adjustments. Because it is less complex, the A1 sight system is more rugged and less likely to be knocked out of zero but in theory has less granularity in adjustments.

To set mechanical zero run the rear sight in one direction, left or right, until it stops. Count the number of clicks in one direction, then again going the other direction until it stops. Divide by two. Then count that number of clicks in toward center. Record this. For the A2 turn the elevation knob to the 8/3 position and then 1 more click clockwise. Adjust the front sight until it is level with the sight post. You are now at mechanical zero.

Fire groups of three shots at the zero target from a distance of 25 yards. Find the center of your groupings and measure from there to the central vertical and horizontal lines in order to determine how far you need to adjust the sights. Lines on zero targets are in 1” increments from the center of the bullseye. To move your groupings to the left, turn the windage knob on the rear sight to the left and to the right to move your grouping to the right on the target. Looking from the top of the sight, the front sight post will need to be turned clockwise to raise groupings and counter-clockwise to lower them as they appear on the target. Repeat until you can consistently hit center mass.

Now that your Iron sights are at setup, let’s briefly discuss how to choose a scopes. First you need to decide what you want the scope for, Home defense, plinking, competition, or long range? With those questions in mind, consider the below:

 

1. A more expensive scope is usually made better.

2. A larger objective lens, the glass facing your target, can gather more light.

3. A larger scope allows more light transmission and usually enables more adjustments.

4. There’s really no reason to buy a scope that can outrange the ammo you’re shooting.

5. Lower magnification means wider field of view, which means it’s easier to acquire your target and keep on top of the situation around it.

Red dots can enhance you scope or be used alone. When used alone they allow you to remain focused on the target with both eyes opened. These sights allow you to point and shoot by placing the “dot” on the target and pulling the trigger. Red dot sights offer maximum available light transmission and wide fields of view. They are considered the fastest sights for target acquisition and also offer unlimited eye relief.

Let’s talk about the most common mount for your red dot and / or scope, Picatinny rails. The Picatinny rails are military standard MIL-STD-1913 (AR), which was adopted on February 3, 1995. They are the most common rails on modern AR-15 rifles. The recoil grooves are consistently spaced allowing manufactures to provide consistent and secure mounting hardware.

REFS:

https://info.stagarms.com/blog/bid/378263/Zeroing-the-Iron-Sights-on-Your-AR-15-Rifle

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AR-15 Barrel Extensions Retention

Correct barrel installation is very important. An incorrectly installed barrel can cause serious injury or death. We are going to discuss the correct way to get your barrel installed. First thing we need to do is gather up some tools and supplies:

Armorers wrench, torque wrench, punch, gas tube alignment rod, receiver clamp and / or padded vise, and grease. A grease like AeroShell 33MS or MCARBO designed for aircraft and graphite free is what you will need. Without the proper grease, your upper and barrel could eventually suffer from galvanic corrosion, galling, crack and come loose.

1. Grease the barrel extension prior to installing into the receiver.

2. Align the index pin with the recess in the upper receiver.

3. Push the barrel and upper together so the index pin fits in the slot. It is OK to use a rubber mallet to install the barrel to the upper if things are too tight.

4. Apply grease to the threads of the upper receiver and hand tighten the barrel nut assembly on to the upper.

5. With your torque wrench and armorers tool tighten and loosen the nut 3 times to seat the threads. Use the torque wrench to tighten only! Use your armors wrench to loosen. The goal is to align the space between the teeth at 12 o’clock.

6. Torque from a minimum of 30 ft lbs to a maximum of 80 ft lbs. Your goal is to align a gap between the teeth to 12 o clock of the upper to permit the gas tube to slide through. Once torqued, the gap in the delta ring, weld spring, and C clamp will need to be positioned to 12 o’clock as well.

a.) If it won’t line up, the easiest, and safest method is to order a barrel nut shim. If you are going to be doing several of these, might be worth having a few on hand. These are thin shims that will be installed in the barrel nut to help align the next gap / tooth. Follow the instructions included with the kit and it should fix any alignment issues.

7. Slide the gas tube into the upper receiver.

8. Push the front of the gas tube into the front sight / gas block base. There will be two holes on the end that goes to the sight post / gas block, one hole for the gas, another for the roll pin. Align the holes and use a punch to install the roll pin.

9. Drop on your hand guards and you are done.

REFS:

https://youtu.be/ey3cIB5u7q4

https://youtu.be/h_tELLisZMw

http://www.thenewrifleman.com/ar15-barrel-installation-guide/

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AR-15 Direct Impingement and Piston-Driven

The original, Eugene Stoner AR 15 firearms are what is called direct impingement. When the bullet is fired it goes screaming down the barrel, as it passed the gas block it directs some of the gas down the gas tube into the gas key on the bolt carrier pushing it back and cycling the weapon. Excess gas is vented to the upper and lower receivers. For the sake of this paper that is the simple description

Now piston operation works pretty much the same up to the gas block. When it gets to the gas block most of the gas is vented into a piston and pushes a rod back that pushes the bolt carrier back cycling the weapon. The excess gas escapes at the piston by the gas block. Again, very simple terms.

1. Piston-driven guns run much cleaner. The gas is vented at the gas block versus venting into the upper and lower receivers.
2. On average, piston-driven guns cost more. There are some very expensive gas impingement ARs and some inexpensive piston-driven AR rifles. However, if you want to purchase the least expensive AR possible, it will be a gas impingement gun.
3. Gas impingement guns are more suppressor-friendly, especially those with an adjustable gas block that allows you to control the amount of gas directed back through the gas tube. It should be noted that with both systems, your rifle will fire dirtier with a suppressor.
4. Piston-driven guns run cooler. The gas that enters the upper and lower receivers is hot, making what is touches hot. On a piston-driven rifle the hot gas evacuates at the gas block, further away from your hands.
The one item that has a lot of controversy is the accuracy, many say that the direct impingement is more accurate. I am going to leave that one alone until I can check myself. Both piston-driven and gas impingement guns are very reliable. If I had to pick between a gas impingement and a piston-driven AR, I think I would try the piston driven, simply because I have not tried it yet and the research sounds like it might be a great option except for three things: parts for gas impingement ARs are easier to find, much more plentiful and less expensive. Still think I’ll do it.
If you own a gas impingement AR and want to try a piston-driven AR, just purchase a piston-driven upper receiver. Since the gas impingement and piston systems work independently of the lower receiver, you can alternate between both on the same lower receiver.

REF:

6 Facts About AR-15 Gas Impingement Vs. Piston

Build an AR-15: Direct Impingement or Piston Operation?

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A Word About Ammo

Choosing the right round for your AR build is one of the first things you should consider in your build process. With so many options ranging from .22 long to .50 BMG it is not an easy task. Several factors need to be taken into consideration, what will the rifle be used for? Plinking, home defense, large game? Does the cost per round and availability meet my needs? $3.78 a round for .50 BMG is a little expense compared to $0.48 for 22LR for frequent range trips and general plinking. Other considerations are barrel length and twist. Heavier bullets require more twists, 1:12 and longer barrels while lighter bullets can use shorter barrels with less twists, 1:7.

There are four major bullet types:

Full metal jacket (FMJ): a harder metal like copper, steel alloy, or gilding metal wrapped around a soft core usually lead. Sometime referred to as ball ammo. Inexpensive and good penetration are characteristics of this type.

Jacketed soft point (JSP): a harder metal like copper, steel alloy, or gilding metal wrapped around a soft core usually lead but with the lead tip exposed. This allows the round to expand on impact creating a larger wound.

Jacketed Hollow point (JHP): a hard metal like copper, steel alloy, or gilding metal bullet with a hollowed tip. It is designed to create a mushroom shape on impact decreasing penetration allowing for less collateral damage.

Boattail (BT): a hard metal like copper, steel alloy, or gilding metal bullet with a shape of a boat. This allows for a more stable and accurate round. Usually used in competitions.

A way to save money on the ammo mentioned above is to purchase surplus. Surplus ammo comes with other, non-monetary cost. It usually uses corrosive primers and/or has been sitting in storage for a bit collecting dust and dirt. One way to mitigate the corrosion is with ammonia, the amount in window cleaner is enough to get the job done. Just flush your upper with some cheap window cleaner when you are done shooting. Then when you are home clean and lube everything up, just like you do after every range trip. Not so much with 5.56 surplus ammo anymore but something to keep in mind with surplus ammo is that it is not marked well. You might not know what is in the projectile. It might be steel or other material that is not indoor range friendly.

The caliber and twist of your AR 15 is normally stamped on the barrel, if not, check the literature that came with your barrel or rifle. The 5.56 and .223 rounds are close, but not identical. The .223 is a civilian round and has Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) specs while the 5.56 is a military round that has their own specifications that might require higher pressure for higher velocity. As a rule of thumb, 5.56 chamber is OK to fire both 5.56 and .223 but .223 chamber is not OK to fire only .223.

Surplus ammo plays a role in the cost effectiveness of reloading. With the cheap price of surplus ammo it is not cost effective to reload those calibers. I think you start seeing a return on your investment when you start reloading “off” or custom calibers. Your presses and other equipment’s can cost a couple hundred dollars to your total cost of investment. If you are not reloading to save money but rather to get better accuracy with a better round or as a great way t relax and get more involved with your complete shooting experience, then reloading is for you.

REF:
https://en.wikipedia.org/wiki/Full_metal_jacket_bullet
https://en.wikipedia.org/wiki/Soft-point_bullet
https://en.wikipedia.org/wiki/Hollow-point_bullet
https://ammo.com/bullet-type/full-metal-jacket-boat-tail-fmj-bt

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Starter on AR-15 Problems

There are a few areas of consideration when assessing issues with the AR-15 style firearms.

1.) Is the firearm new from a factory? If yes, is it a reputable manufacture, or fly by night?

2.) Is it a new home built? Is this the builders 1st or 50th?

3.) Finally, is this a used rifle that has been fired many times and just started to malfunction?

Ammo and routine maintenance are other items that should be looked at for all 3 considerations. Is it good quality ammo? Hand-loads? Cheap Ammo? When was the last time the rifle was cleaned?

First things first, clear the weapon, make sure it is safe and preform a function check. If the function check fails and it is a new rifle, you might want to send it back. If it is a new home built check that the springs are installed and installed correctly, in the right direction and place. If it is used and just started happening, check for spring wear and replace as needed. The hammer spring is a common culprit of many issues to include intermittent firing, misfires and light fires.

Bad gas can cause a lot of problems like short stroking which can be caused by an improperly staked bolt carrier key coming loose. Another spot to look is if the gas rings are missing or damaged, this is usually on the used rifles. On home built rifles especially, make sure the inlet and the gas port are properly aligned, tightened, and the correct tube is being used. An incorrect or misaligned gas block is a common culprit.

A failure to eject scenario can be cause by extractor and ejector springs. Would not hurt to have a few of those around the shop. Weak springs can cause the spent casing to get caught in the ejection port causing a stove pipe situation. Tell tail signs of ejector/extractor issues are dented cases, round rim markings like scratches or damage to the stamping at the bottom of the round. Inconsistent round ejection is another sign, if you test fire the weapon 3 times and the brass ejects to 3 very different angles, you have an issue. All 3 rounds should end up in a pile close to each other.

Talk to the person bringing you the rifle with the 3 questions above in mind. This will help you narrow down the issue and get the weapon back to your customer quickly. The AR-15 is a reliable weapon and with some initial questioning and test fires as required, you can quickly diagnose the issues and fix it.

REF:

YouTube – Various Michael Bell videos

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