AR-15 Build Problems

As a military armorer for over a decade I conducted many studies on the AR-15. Meticulous record keeping helped. I have passed along the results of my research in these pages over the past couple of years. The techniques described helped me to cut the average group size of the Army Reserve Shooting Team National Match AR-15s fully in half. Because I have written solely about the ideas that worked it occurred to me that perhaps I have been misrepresenting the truth a little, though not on purpose.

I have tried things that flat didn’t work. There are folks out there that swear by some of these 22 Magnum, also use fixed ejectors. Bottom ideas. This will likely ruffle some feathers but I have been a tax assessor, state game warden, and drill sergeant in the past so I am used to making people angry. Ejector Tension Weapons designers have incorporated various methods of ejecting spent cartridge casings. For example, 1911 pistols have an extractor on the right side of the slide’s breech face but nothing else.

The spent casing is pulled from the chamber by the extractor as the slide is propelled to the rear upon firing. A fixed ejector is mounted on the left side of the frame. When the fired cases left rim hits the forward face of the ejector it is diverted to the right and out. Fixed ejectors are not exclusive to just pistols. Both of my Anschutz squirrel rifles have fixed ejectors. Spring-loaded ejectors have a plunger in the bolt face. When such a firearm chambers around that plunger is depressed flush.

The coil spring is compressed and applies forward pressure to the ejector. With the bolt moving rearward, pressure to the right by the ejector wants to push the casing but the casing can’t move until it clears the chamber and is flung out of the rifle. Many folks are under the impression that the hard pressure on the left side of the cartridge rim by the ejector causes the whole cartridge to cock at an angle away (to the right) from the centerline of the bore, negatively impacting accuracy.

The fact that gas guns generally tend to have fatter chambers certainly lends credence to this theory. Folks subscribing to this theory often make modifications to the bolt that result in less ejector pressure. Doing so can run the risk of malfunctions, but is there any measurable accuracy gain? I tested a number of 20" sub-minute Service Rifle uppers in a machine rest using known lots of ammo. Then I removed the upper and took the ejectors out, testing with the same ammo.

There wasn’t a lick of difference between the groups. As a second attempt, I repeated the test using 26" Match Rifle uppers. Both the 20" and the 26" barrels were chambered with my normal gas gun Wylde reamer. I followed the same basic procedure as with the first attempt and the second

Above center: Bolt carrier weights influence barrel harmonics. test largely confirmed the result as the groups fired with no ejectors were a measly 3% smaller. Even High Masters can’t benefit from a mere 3% accuracy gain when shooting from the shoulder. If one test showed zero accuracy gain and a second showed only a 3% gain when ejectors are completely removed from the firearm, it’s logical to conclude that leaving the ejector in the bolt and using reduced ejector spring tension is a poor idea.

There is likely to be a zero accuracy gain at a potential sacrifice to reliability. Don’t mess with the ejector and just leave it as Stoner designed it. Buffer Springs Manufacturers of chrome silicon flat wire buffer springs claim that they ensure "consistent forward thrust" on every shot.

Just as consistency in the application of shooting fundamentals results in top scores, I have determined that consistent bolt carrier velocity helps ensure uniform positioning of the case rim on the bolt face with equal pressures by the extractor and ejector for every shot and uniform positioning of the cartridges in the chamber for all shots. The result is improved accuracy and the use of match bolt carriers and bolt carrier anti-tilt pads enhances grouping capability by 8.8 and 14%, respectively.

I wondered if the advertised consistency in forward thrust of the more expensive springs might also buy some added accuracy so I tested my theory with 12 AR-15s. Each gun was first machine rest tested using known lots of ammo, magazine fed. Then the flat wire spring was substituted for the stock spring and the test was repeated. Seven guns responded favorably and their average group sizes tightened up by 13.8%. The other five guns failed to improve.

While I had no malfunctions during testing the various manufacturers of these springs nearly all use words like "extra power" in their advertising. I have known shooters who tried these springs to find their function compromised and they had to go back to stock springs. Any time you make any changes to the bolt carrier, the buffer, or buffer spring you can expect point of impact changes. Confirming zero is a good chance to confirm reliability.

Given that only a little over half of the tested dozen guns showed any improvement with the springs, I would advise using these springs only if your gun is similarly benefited. For you grown ups, Glen Zediker noted in The New Competitive AR15: The Ultimate Technical Guide that accuracy enhancement in the AR-10 with the chrome silicon flat wire springs showed much more favorable improvement. I have not personally tested these springs in the bigger rifle and will take Glen at his word.

It is very seldom that his research differs in conclusions from mine. Recoil Reducers Recoil reducers or cyclic rate reducers resemble automotive shock absorbers. They soften the secondary recoil pulse felt recoil, which occurs when the back of the buffer slams into the rear of the buffer tube. That abrupt stop has a jarring effect to the shooter that combines with the recoil caused by the forward acceleration of the bullet.

One of the claims these reducers is to "Improve Accuracy." Although I have shoulder fired a few of these devices I have never tested them in the machine rest for accuracy, though I’d expect to see much the same as with the flat wire buffer springs. I would think that accuracy would be very gun specific.

What I have experienced with guns having reducers when shoulder firing them was that felt recoil was noticeably less, zeros changed quite a bit from the same gun without the devices, in tens of thousands of shots I never had any function issues (though testing is always necessary), and my scores went up on courses of fire where time limits were fast. That doesn’t necessarily indicate accu-

The idea for the tungsten unit came from M9 KKM barrels with tungsten bushings. racy improvement, just that faster recovery between shots was spent getting better sight alignment for the next round. Bolt Carrier Weights Bolt carrier weights are supposed to increase the dwell time, keeping the bolt locked up a little longer, aiding in primer retention, possibly allowing increased powder charges.

When the Army Reserve was experimenting with 90 grain .223 bullets we were trying to keep bullet velocity above 1,100 fps at 1,000 yards. I did my load development work with these weights and felt they were worth about 0.3 grains of extra propellant, gaining about 30 fps in velocity. Some folks are of the impression that a secondary value of the weights it to increase accuracy. In some firearms this will be true but in about as many others they don’t help or can degrade accuracy.

These devices can add up to four ounces to the carrier assembly. The carrier is apart of the barrel during firing because the bolt is locked up with the barrel extension so a radical change in the weight of the carrier assembly is going to influence barrel harmonics and that can hurt or help accuracy. If you are going to use these, have them in place during load work ups. Expect to have zero changes and a performance drop off if you forget to reinstall them.

I don’t recommend leaving these weights in during magazine-fed rapid fire strings as they can induce malfunctions. If you wish to use them during rapid fire, there is a simple modification to the end cap of the buffer which the manufacturer thoroughly describes in the instructions. Tungsten Various non-sensical laws have restricted flash suppressors and shooters affected have contacted me for something to cover up the threads at the muzzle. I made up simple thread protectors.

While making these I remembered that accuracy work with the M9/Beretta 92 pistol found that a prime reason it shoots fat groups is lack of forward support to the barrel. There is no bushing in the slide such as in the 1911 and the muzzle is unsupported. Early gunsmiths cured this by threading the front of the barrel and screwing on a bushing locking up with the slide. Early designs used regular steel until some smart hombre decided to try tungsten. Tungsten is much heavier and stiffer than regular steel.

It is also very hard to machine. It is available in several grades and only the "softest" grade works in the pistol applications. Pistolsmiths using the tungsten bushings claim enhanced accuracy by improved harmonics. There is no doubt that stiffening the front inch of the barrel in addition to hanging that much more weight out there does influence barrel harmonics. When I was the Armorer for the Army Reserve Shooting Team I outsourced some of the work to various

specialty shops. Most of my earlier work was in gunsmithing revolvers for police. As they migrated away from wheel guns, I worked on 1911s and Berettas. When I had so much AR- 15 work for the Team, I outsourced M9 accurizing to Mountain Competition (MountainCompetitionPistols.com, Tungsten M9 barrel bushings were an offered option. When I decided to try tungsten thread protectors I contacted them for advice.

Pistols use a different thread than the AR-15 but it was close enough to allow a judicious "re-tap" to get it to fit. Mike Harpster, a local gunsmith I outsource some of my work to (DeadCenterSports.com, performed the machine shop modification. They feel noticeably heavier. I pretest all the AR barrels I sell on a machine rest for accuracy and make the groups available to my customers so they can select a barrel that is the best compromise of price and accuracy to meet their needs.

I had just received a shipment of Bartlein gain twist barrels and was finishing up their break in when the thread protector project was coming to fruition. Using the pre-ban configuration barrels I ran three tests with known lots of ammo using a normal A2 flash suppressor, a regular steel thread protector, and the tungsten unit. 1/3 of the barrels tested liked the normal A2 flash suppressor, 1/3 shot best with regular steel thread protectors, and the final 1/3 favored the heavy tungsten unit.

As with other tests, my study of the tungsten thread protectors found firearms to be individuals with particular preferences and I chose not to sell tungsten protectors. Without machine rest testing a customer would have no idea if his barrel would be one favoring them. Why didn’t the tungsten thread protectors have the desired outcome of improved accuracy? An M9 barrel is five inches and the tungsten bushing occupies the front inch, or 20% of the total length.

Contrast that to a 20" barrel and a thread protector between 1/2-5/8" long. The tungsten part is about 2.5% of the total length. So perhaps part of the answer is we are just not using along enough section of tungsten to have a positive dampening effect on barrel harmonics. Long Chambers Long chambers are those in which the combination of free bore and throat causes magazine-length rounds to jump enormous distances before encountering any rifling.

There are a few folks out there that try to convince us that magazine-length ammo is jump proof and that these long jumps don’t hurt performance. I’m not aware of any studies that support the veracity of such claims and believe these assertions are examples of "encyclopedic error" where claims have been repeated so often that they have become accepted in spite of any empirical evidence.

I have set up and conducted studies into this bullet jump theory with details covered in my July-September 2014 articles "AR-15 Chamber Selection." Summarizing that, my studies revealed that some bullets are jump resistant but none I tested are jump proof. All bullets degrade in accuracy the further they are jumped, all other things being equal.

If you are building a gun shooting some or all of the time with 2 1/4" magazine-length ammo and you want both accuracy and longevity, I would back away very smartly from any barrel with a chamber longer than a Wylde. Recoil Compensators While I haven’t tested all the recoil compensators on the market, most true compensators are closed in at the front with the hole in the front just large enough to allow the bullet to pass through without rubbing the sides.

This design causes the gas following the bullet to be directed upward, dampening muzzle jump. The GI A2 units are open in the front, similar to the A1 flash suppressor but closed at the bottom to reduce dust signature when firing in dry conditions from prone. Recoil compensation, if any, is minimal. True compensators do make a noticeable difference in felt recoil. If I were burst or full auto firing at modest distances I would sure want one of these devices.

That said, there are a few downsides from the ones I tested. Point of impact changes when installing these. I have had a gun firmly clamped in the ma-

chine rest with bullets going nearly through the center of a 4’ x 4’ target backer at 100 yards and switching to a compensator would put rounds clear off the backer! I have also tested a few of these for accuracy and wasn’t impressed. Some groups nearly doubled with the compensators in place. Perhaps I just haven’t tested the right compensators. Certain match rules disallow their use, including NRA events. I have mentioned some of the things to look for regarding compensators.

I suggest that if you are interested in the potential use of them you conduct your own tests to see if they provide an advantage in the style of shooting you are involved in. Gas Ports And Velocity Another encyclopedic error I’ll debunk is the notion that gas ports in our AR-15s drain off gas that could be used to raise bullet velocity. It seems to make sense. Gas ports in 20" barrels are nearly 1/10" in diameter and about 7" to the rear of the muzzle. The bullet is still accelerating in that last 7" of barrel.

One would suspect that a gas port of that size could drain off gas that would be valuable in speeding up the bullet before it exits at the muzzle. What happens in real life? I use adjustable gas blocks from JP Enterprises in my rifles which have set screws that can be adjusted to meter gas or shut it off entirely. For this test I fired a ten-round group with the port in the full open mode through my Oehler chronograph, then set the screw to completely shut off the gas for a second group.

There was zero loss of velocity. In Derrick Martin’s The Complete Guide To AR-15 Accuracy, he recounts the same results performing a similar test. There is a handy estimate used even by big ammo makers and applied across many cartridges, not just the .223, stating that for every inch of barrel increase or decrease one can expect about a 25 fps change in velocity. I have only sometimes found this to be an accurate estimate.

Comparing the velocity of an M4 barrel to a full-length 20" AR-15 barrel the formula holds pretty well with a predicted 150 fps velocity difference. When one attempts to apply the formula to longer barreled guns the formula seems to overstate expectations. Chronograph readings on the difference between 20" Service Rifle tubes and 26" Match Rifle ones yields about 100 fps difference, quite a bit below what the formula predicts.

Derrick Martin mentions similar testing in his book and he came up with a difference of just a little less than the 100 fps I found. I took it one step further and compared 24" barrels to 26" ones and the difference was only 27 fps. Not 27 fps per inch but 27 fps total. The conclusion that I draw is that the 25 fps per inch is fairly accurate when comparing barrels in the carbine to "normal" 20" length but overstates things with regard to longer barrels.

It also appears that one is getting most velocity out of 24" or 26" barrels and going longer in barrel length probably can’t be expected to give more. AG American Gunsmith Reader Services 1.