Do You Have Gas? Part One

The two most common questions I’m asked about match AR-15s have to do with trying to predict barrel life and how far to jump heavy bullets used in long range competition. Fortunately, "What’s wrong with my AR?" is way down in the frequency of questions I field. That’s a good thing because no AR-15 armorer really wants to hear that question. While there are a whole bunch of things that can go wrong with the rifle, these seldom happen. Eugene Stoner designed a great rifle. My degree is in Wildlife.

When attending Penn State the professors told us to always first study any existing body of research before going to all the work of setting up a study on some critter or new management notion; a good "work smarter, not harder" philosophy. When the editor asked me to write on this topic he mentioned a very well written article, "A Primer On AR-15 Problems" by RK Campbell in the March 2011 issue. I dug it out and read it, and strongly suggest that you do as well.

Another great source on the topic is The Complete Guide To AR-15 Accuracy by Derrick Martin. He devotes a whole chapter to the subject and offers a lot of good information on trouble shooting and repair on the various carbine versions. When that book was first published in 2000, gunsmiths were just getting the nuisances of the carbine figured out. In general, I think carbine design and manufacture has improved since and I don’t hear complaints about function and repair nearly as often.

One tome that certainly helped was Glen Zediker’s The Competitive AR-15: The Mouse That Roared. This was first printed in 1998 and mine is from the 14th printing, indicating many shooters found it to be of worth. I suggest spending some quality reading time on the chapter on cleaning, especially the parts on lube. Zediker’s The Ultimate Technical Guide was printed in 2008 and has a chapter ("Maintenance, Cleaning and Malfunction Cures") covering this specifically.

Another great Zediker reference is The Competitive AR-15 Builders Guide. If you use the correct parts as identified in The Mouse That Roared and put them together as per the instructions in Builders Guide your chances of having a relatively break proof gun are really enhanced.

All these references, even the sections that aren’t specifically geared to diagnostics, assembly and maintenance, will help you understand how Stoner platform guns work and your greater understanding will lead to developing a routine to better troubleshoot problems. Some of the military manuals can be quite helpful and have great sections on assembly and disassembly. I also like them for tables on torque limits and similar specifications.

Living with the gun will teach you its few weaknesses and vulnerabilities like no other experience in the world. I have slept with Stoner platform rifles in nearly every English speaking nation in the world as well as in a few fox holes in some non-English speaking "garden spots" where, thanks to our politicians, our military seems to find itself all too frequently. Sleeping in fox holes while mortar rounds whistle overhead isn’t nearly as "attractive" to me at my current age as it was when I was between 20 and 40.

If you feel the same way then I suggest you might want to consider a little compromise and just try competitive shooting. My friend, the late Jeff Cooper, once said, "A man will push himself harder in training to win a little gold medal than he will train to save his own life in combat." As in most things, I think that Chairman Cooper was right on.

I never trained nearly as hard before going into combat, even with a Drill Sergeant’s boot up my butt, as I did to earn three Distinguished Medals, the President’s Hundred tab, and the German Armed Forces Badge for Weapons Proficiency (Schützenschnur.) Training to win will stress both yourself and the gun, and you will learn much more about both in the process.

Standard Required Caveats "The Gun Writer’s Union" requires all of us who write on the topic of semiauto malfunctions to say somewhere, "most malfunctions are caused by bad ammo, bad magazines, or failure to properly clean and lube". There, I have done said it and my obligation is fulfilled so I am not sanctioned or charged extra dues for failure to include it. Seriously, whenever I am asked to diagnose function problems for a customer I always ask for magazines and a sample of his ammo.

When it all arrives I give a good visual inspection to determine the condition and cleanliness of all three. The gun, obviously, also needs some lube. I do get a lot of questions about what lube to use. I usually answer, "I am a former military armorer and, therefore, a whore by definition. I have never seen a gun lubricant that I don’t like."

Most any lube is better than no lube. And I have never found a lube good enough that it is a substitute for cleaning for any length of time. I know that some people have strong opinions about which lube is best, usually with a list of good reasons to support their opinions. The next guy I talk to likes some other lube and gives pretty much the same reasons. I’ve just never gotten all that emotional about which lube to use as long as you are applying something.

I maintain that if you thoroughly clean the bolt carrier assembly, and wipe out the area where it lives in the upper receiver, and wipe off the charging handle and then apply some lube of your choice every time you shoot the weapon it should be reliable enough on its next outing. And it will be more accurate because the bolt carrier velocity will be constant resulting in consistent positioning of the cartridge in the chamber and equal pressures on the cartridge head from shot to shot.

If you abuse your firearm or insist on neglecting it, don’t blame malfunctions on the brand of lube. After performing a visual inspection, if I don’t discover anything obvious I like to actually fire the gun using the customer-supplied ammo and magazines. Depending on what type of malfunction I am seeing may point me in the direction of a quick diagnosis and repair. If it doesn’t, I like to substitute known good ammo. If the firearm continues to malfunction, I substitute a known good magazine.

Continued malfunctions is a pretty good guess that Union mandated caution statement doesn’t apply and you really do have a gun problem. Conversations with the customer also helps. Ask if the firearm has a past history of the same function problem, or if he has changed anything recently like magazines or ammo and if the function problem began about the same time as something new was introduced.

Has he replaced any parts in the rifle at about the time the problem surfaced? "'What’s wrong with my AR?' is way down in the frequency of questions I field. That’s a good thing because no AR-15 armorer really wants to hear that question. There are a bunch of things that can go wrong with the rifle but these seldom happen. Eugene Stoner designed a great rifle." Is there only one problem with the firearm or are there multiple, seemingly unrelated, issues?

Gas Problems In a social setting this is easy, because everyone in the room moves away from you. With firearms, not so much because problems not related to gas can give similar symptoms, just as smoke coming out of the exhaust pipe of your car can be caused by several culprits. Most gas related function problems in firearms are caused by not getting enough gas where it needs to go.

There are some neat problems that can occur if you have too much gas in a gun but we will save those for another time because they are way less common. A common symptom of not getting enough gas is failure to eject. Simply put, the bolt isn’t propelled back far enough to allow the spent casing to exit the ejection port. But failure to eject can also be caused by a problem with the ejector itself. I always look at the most obvious connection first. If there’s an ejection problem, look at the ejector first.

If the ejector checks out, go back to looking for gas issues. A handy diagnostic at this point is to charge the magazine with only one round and fire it. If the casing fails to eject and the bolt carrier doesn’t lock back, lack of gas is looking more like the guilty party. I had an interesting experience with these same symptoms and diagnostic trail recently.

All the same bread crumbs, however, she was also complaining about losing the second stage from her fancy National Match trigger at about the same time, saying her hammer was failing to recock part or most of the time. Her gun had a fairly short chamber, so perhaps she had blown a primer and that it had lodged in the trigger group, making the hammer offer more resistance to the rear travel of the bolt carrier.

A primer down in there often just stops the trigger from operating, not usually causing just one stage of a trigger to go out. Cocking the hammer confirmed it was gritty and difficult to pull back. Examination with a flash light revealed parts swimming around in the well where the trigger group lives. After pouring the two parts out, one was a very mangled coil spring and the other a fine hex head screw.

There was a hole in the top of her trigger, which was the female threaded area where the coil spring and adjustment screw for her second stage trigger let off used to live. Somehow the screw had backed out, and it and what had been a captive spring had fallen out. The spring had gotten up under the hammer was making the hammer jam up. The added resistance to hammer cocking caused by the spring being down under the hammer was slowing the bolt carrier and causing the ejection issues.

What at first blush appeared to be a gas problem turned out not to be as I failed to quiz her about "other problems with the rifle occurring around the same time" as the ejection problem. The trigger assembly was from around twenty years ago when the two stage National Match triggers were just getting popular and hadn’t been made in years. Even in

its boogered form the spring looked familiar to me, so I got out some personal two stage triggers made by Charlie Milazzo, the man of two stage AR triggers. He also used the 2 stage adjustment idea with a hex head screw and captive spring. The springs in the Milazzo triggers looked like the one from my customer’s gun and both still looked familiar. Concentrating on match ARs I seldom work on regular rack grade ones these days and I guess that is what took me so long.

I dug out a conventional GI trigger and, staring me in the face, was a disconnector spring which looked just like those in the match triggers. I tried fitting it but the second stage failed to make the CMP and NRA-mandated weight of 4.5 pounds. I dug out another spring that looked about a coil longer, being new and simply hadn’t taken a "set" and was easily able to adjust it to make legal weight.

Given that the set screw had backed out once I put a distinctive witness mark on the head of the screw and told my customer to check the rifle every time cleaned it and that excess grease, oil and crud would necessitate repainting it from time to time using a common paint or nail polish to keep that mark easily visible. She’s back in business and has more money in postage invested than the cost of the actual repairs. Function is now back to being 100 percent and what looked like a gas issue wasn’t.

I ended up learning a valuable lesson about those second stage coil springs that may help you as well. While you will probably never take in a gun whose trigger has fallen apart like this one you may have one that just won’t adjust up to make legal weight. Substituting anew GI disconnector spring for one that has taken a set may get you back in business. An easy win!

Army Reserve Experience Competition experience with the Army Reserve Marksmanship Program and elsewhere has furthered my knowledge of Stoner platform rifles. I learned a valuable lesson about the gas system while competing at Bisley Range in Surrey, England. This was probably 20 years ago and our team American Gunsmithing Association

was competing in an international combat match with other NATO countries. Although the British issue ammo met 5.56mm NATO specification, our M16s were running funky and dirty with the stuff. My rifle didn’t like it at all. We began diagnosing why I was having so much trouble and discovered that my fairly new bolt carrier never had the screws holding the bolt carrier key in place staked.

This allowed both screws to back out a little and there was a gap between the top of the carrier and the bottom surface of the key which was allowing gas that should have been impinging on the bolt to escape. The rifle was robbed of gas and I was in big trouble. I borrowed some high pressure aerosol gun scrubber, red Loctite and an Allen wrench from team members. We hosed off the gunk, let it dry and slopped it together with liberal amounts of Loctite and a strong hand on the wrench.

We didn’t have a torque wrench to hit the 35 to 40 inch-pounds called for in the military manuals and would likely have erred way on the heavy side even if we did. Not only did the bolt carrier survive the next two weeks of shooting but I managed to win some events in the process. Nearly 20 years later that carrier is still 100% functional. While I don’t stake the screws in all that time, I would never go to another country with a carrier that didn’t have them staked again.

One would think that hot gas passing though the key would overheat red Loctite but I have never had a lick of trouble. I did relegate the carrier just for practice after I got back, just in case. You will probably seldom run into a carrier with key screws that haven’t been staked. I guess mine was just overlooked at the factory. Companies are more careful now and I haven’t seen but one other carrier (it came from the same company) since that was missed.

You may have to stake a key in the event of performing a repair job, however. If a bolt carrier is dropped from much distance on a hard surface the key may be bent. Obviously, this can cause function problems. Of equal concern is accuracy. The alignment of the gas tube to the key is critical to accuracy. The smallest bit of misalignment will slightly cock the carrier and with it the bolt face.

Orientation of the cartridge in the chamber will vary from shot to shot as will pressures of the bolt face, ejector and extractor on the cartridge rim. I have found that fatter group size and frequency of fliers often result. The military manuals explain how you can supposedly "iron out" key wrinkles using a 0.175" and 0.180" diameter punch and inserting it through the front, lightly tapping or applying pressure to straighten as needed.

The closest I can find is a 3/16" (0.1875") which is oversized by the manuals and seems just a bit too fat on keys I’ve tried it in. If you elect to repair using this route you will need to turn down the business end of the punch by about 0.008". Using this approach will prevent having to remove the original, already-staked key. Be sure to thoroughly check alignment of the gas tube with the key following your repair or accuracy will suffer.

If the severity of damage is too great or you don’t want to mess around making up a custom tool, replace the key with anew one. They are not that expensive. Obviously, if you take this route the new replacement key will need staked. Less obvious is the fact that you will need to recheck the alignment with the gas tube when finished. When replacing the key note there are manufacturing tolerances involved so there is no

guarantee of proper alignment. It’s useless bothering with premium barrels only to fail to get all the accuracy out of the rifle because you rushed assembly and let a misaligned gas tube slip through. A the references cited in Part One will show, there are differing ways to do this, however, everybody agrees you should not recycle the old screws. Buy new ones! Brownells carries them and they are cheap. You can also get them at hardware stores, sized 8-32 X ¼.

The screws designed specifically for use on the AR have knurled heads, extra insurance to enhance the staking and making back out less likely. Reference sources differ regarding the use of adhesives. The military manual I have does not address them. Glen Zediker recommends red Loctite. I would be inclined to use the red #271 on the screw threads because it’s designed for threads with green #638 better on flat bearing surfaces.

Young Manufacturing recommends Permatex High Strength Thread Locker available from Ace Hardware, part number 27010. The military manual says to torque the screws to 35 to 40 inch-pounds. Note this isn’t the more common (heavier) foot-pounds those of us working on ARs are used to. You can Google up conversions from inch pounds to foot pounds but many of us may not have a torque wrench calibrated in the lighter inch pounds.

Brownells has inch-pound torque wrenches but most ain’t cheap, however, Borka International offers a more affordable unit. Glen Zediker recommends exceeding the military torque limit but doesn’t say by how much. Young Manufacturing lists 56 inch-pounds and I am inclined to go with that number. The screws made for this will likely take a 1/8" wrench size and whatever adaptors you may need to fit that to your wrench.

Glen Zediker points out that it is not a good idea to just jump on one screw and take it all the way to final torque in one application. I would snug it up but not to the point where the torque wrench disengages. Then I would go to the second screw, take it all the way down and return to finish the first. The actual staking is a hotbed of contention with almost no agreement. The military manuals say to stake three times equally spaced around the head of each of the two screws.

I use a lot of Les Baer match bolt carriers in my custom rifles and they stake each screw twice, once at the front and back. Use the Starrett 5/32" Center Punch from the Brownells Tool Kit For AR-15 (#827-512-820). Brownells also sells the Carrier Key Staking Tool (#080- 000-638) which supports the carrier while sharpened hex screws press in at the top and form the stakes on each side of the screws. The tool does not use a punch and hammer method like the ones mentioned earlier. J. P.

Enterprises puts two stakes in each screw oriented on the sides and the work appears to be done in some sort of fixture. I use a lot of match carriers from Young Manufacturing and they adamantly oppose any staking at all, voiding any warranty if the customer or armorer stakes their screws. They do, reluctantly, advise that if one absolutely insists on staking to use the Brownells unit. Glen Zediker recommends the Moacks Tool by Michiguns Ltd.

Like the Brownells unit it eliminates the more common punch and hammer method and relies on turning four sharpened hex head screws into the sides of the key screw heads. Which method to use? I said earlier that I have no attachment to any particular method. The Brownells and Michiguns units aren’t cheap but if you are going to be doing a fair amount of staking then either one might be attractive.

Customers expect certain things and staked key screws are one of them so pick the method that is affordable and best suits your shop practices. I would have absolute faith in any key put on with any of the recommended glues and staked in any of the methods described will not come off. Young claims they have and that it was a by product of not enough torque, so I would use the 56 in. lb. that they recommend. Fort Devens Our next story comes from a team training session in Massachusetts.

I was called to the line to look at a flat top exhibiting what appeared to be intermittent low gas. The problem was that it was a hot line and they weren’t about to shut down just because one person was having function problems with his rifle. They were running back to back courses of fire and the shooters were only given just enough time to charge magazines and they were right into the next match. So I would only get about 5 or 10 minutes on the gun before the shooter had to use it for the next string of fire.

That was just about enough time to shotgun it, check one thing, dump in a half bottle of oil, close it back up and hand it to him. My first check was the tightness of the carrier key and it was just fine. The next time I checked the bolt rings and they were also OK. The third time I got the gun my eye drifted to the front sight housing. There was the problem. The gas tube roll pin had just fallen plumb out!

As you know, there is a hole in the bottom of the gas tube that lines up with the hole in the front sight that brings the gas up from the gas port in the barrel. With that roll pin missing the gas tube was free to rotate right, left, or sometimes stop in the center where it should be, the reason why the problem was intermittent. The fix was easy and the firearm functioning flawlessly with the shooter still winning matches with it.

As I passed through the Ready Line I was looking down at shooter’s guns as armorers are prone to do. There was a black AR-15 lying on top of a black soft gun case and about an inch from the front sight there was the black gas tube roll pin

for the gun in question! Fortunately the shooter had not been called to the line yet and I was able to substitute anew pin so he didn’t have to experience the same frustrations as the first soldier. Checking Rings One of my early checks is afield expedient "ring assessment." While not new, it is used by many folks in the AR business. Remove the bolt carrier assembly from the upper.

Hold the carrier at the back with one hand and grab the bolt lugs with the other hand and pull in opposite directions so the bolt will move forward until its movement is halted when the cam pin stops it. The bolt will be in the same position in the carrier as when ejection occurs during the cycle of function. Still holding the carrier at the rear with one hand, set the assembly on a flat surface. The carrier needs to be vertical, resting its weight on the front of the bolt.

If nothing collapses it is a good sign that the rings are in good shape. It doesn’t mean that the rings are "right", however. If I had a gun that was exhibiting apparent low gas problems I would still remove the bolt and check the gaps in the rings. Make absolutely sure that the gaps are staggered or gas can still escape causing malfunctions with perfectly good rings. If the bolt "collapses" into the carrier as when it is in battery with a chambered round, it is an indication the rings are worn.

By no means will every carrier failing this test cause malfunctions as the test errs on the conservative side. I have seen guns fail the test and continue to function flawlessly for thousands of rounds, however, if you have a gun with apparent low gas problems and it fails the carrier test, replacing the rings is sure a good step to take. If the gun continues to malfunction then you have eliminated the obvious and can continue looking elsewhere.

As a professional gun builder I don’t have a lot of spare time for gun cleaning but I obviously recognize the value of keeping the gun clean to longevity, accuracy, and function. It is not unusual for me to clean a customer’s carrier assembly a couple of times during its time here in my shop with an ultrasonic gun cleaner which frees me to perform other work. These units get crud out of little crannies better than any cleaning method I know of with very little effort.

The downside is that they align the gaps in the bolt rings with equal alacrity and predictability. If you clean with ultrasonics you probably already know that you are going to spend an extra minute staggering the ring gaps before you assemble the bolt into the carrier. How often should the bolt rings be replaced? As with barrel life, no one knows exactly because of the variables. Does the shooter dry fire often?

The bolt is moving back and forth (manually to cock the hammer) in the carrier in dry fire, rubbing the bolt rings against the "bore" (the hole in the carrier where the bolt lives) in dry fire too. How often does the shooter clean the bolt carrier assembly and does he do a thorough job? The carrier accumulates crud which wears on the rings (friction.) Crud in the key will also cause premature wear out of the back of the gas tube.

Use of pipe cleaners and ultrasonic cleaners are helpful in doing a proper cleaning of the bolt carrier and key. How often does the shooter apply a drop or two of oil to the rings? In an NRA High Power Rifle 800 Aggregate course, I like to see oil going in around every 20-40 rounds. This is not necessarily directly to make the rings last longer but for function and accuracy.

Consistent bolt carrier velocity relates to uniformity of bolt positioning, orientation of the cartridge in the chamber, and equalizing how the case head sits on the bolt face, pressures of the extractor, and ejector. All this contributes to accuracy. I can tell you that when I machine rest test rifles I put oil on the rings every 20 rounds to control some of these variables. How well polished is the "bore" of the carrier (the hole in the carrier where the bolt lives)? This is subjective.

The bore can be polished using the same tools and techniques as the chamber and I will cover that in another article. What environment is the rifle shot in? I live in Pennsylvania and most of our ranges have nice com) bolt carrier on the left has four stakes located on the sides. Carrier in the center has key held in place with screws and Loctite. Les Baer Custom carrier has four stakes located front to back.

The one on the right has collapsed, indicating rings may need replaced. green grass growing on the firing mounds during the summer. Contrast that to the sand in a state like New Mexico. I suspect that the type of propellant used in the cartridges being fired may influence ring and gas tube longevity with regard to the abrasiveness of the residue. I’ve read pistolsmiths recommending against shotgun powder in pistol cartridges because the shotgun powders left a more abrasive residue.

His comments were in regard to barrel wear but they certainly got me to thinking of the Stoner Platform and gas ring wear. I recommend that you close the ejection port cover (also called "dust cover" for obvious reasons) if range rules permit when not actively shooting. This keeps crud out of the action parts. Use of a soft case is another good idea as long as the inside of the case has less crud than the outside environment. I have seen some that were pretty filthy inside and a good vacuum will help that.

I am sure I am missing other important variables in bolt ring wear. I recycle my bolts because a bolt should outlast two or three barrels but put new rings in. I know guys who put new rings in at the start of every shooting season. Unless a gun is malfunctioning I would recommend not just gratuitously replacing rings right before an important match unless you have at least one range session prior to the match. Most anything you do with regard to the bolt carrier assembly can change your zero slightly.

Rings are cheap. Replace them any time you are having function problems and more often if you wish or if your customers expect it. As with bolt rings, some writers, gun owners and gunsmiths make much to do about gas tubes and how often to replace them. If you look at most gas tubes the back 1/8" or so is the full size of the tube body. I am measuring something on the order of 0.178-0.179" on ones I have in the shop. The tube diameter then steps down a little, 0.166" in those I’ve measured.

The length of that skinnier section can vary but 2.25" is about standard. Then the diameter of the remainder of the tube will go back up to that at the very back, somewhere around 0.178-0.179". Folks will tell you that when that swelled out short section at the back of the tube has worn down about 0.013" to where it is about even with the skinny section in front that this is proof positive the tube should be replaced.

If you have a stripped receiver in front of you, look at the hole which the gas tube passes when it is coming into the gun. You will see that hole is not round. It has four lobes that make it appear like a cloverleaf.

The theory is if the back of the gas tube is too skinny there will be a poor "seal" with the bolt carrier key and gas needed to function the gun will take the path of least resistance and exit the system by back-flowing though the cloverleaf because when the gun is in battery the front (mouth) of the key is right there at the cloverleaf. If I were diagnosing a gun with low gas issues and I observed such a gas tube I would replace it and test fire to see if the gun begins to function correctly again.

One of the problems in correctly diagnosing gas tube wear when the gun is fully assembled is that you can only see about the bottom 90 degrees of the circumference of the gas tube as you observe it looking up through the bottom of the upper when the bolt is pulled back. This visible fraction of the gas tube may look just fine but the ¾ of the tube which you can’t see may be worn more. Properly aligned gas tubes should wear evenly over their whole 360 degree circumference.

I find that far too many builders don’t pay enough attention to getting the gas tube properly aligned with the key, however. Proper alignment has major effects on both group size and frequency and severity of fliers. I don’t put numbers or schedules or round counts on when to replace gas tubes any more than I recommend doing so with bolt rings or barrels. There are many variables involved in all three which complicate things.

With the exception of oiling rings or the internal polish of the carrier, most of the variables relating to ring wear out also apply to the gas tube. Since gas tubes are about nine times the cost of a set of rings I don’t want to replace one unless it is really necessary. Whenever replacing a gas tube be sure to ensure that the new one is properly aligned with the carrier key. Just because it is new is no insurance that it will automatically align right! AG