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Posted: 11/17/2004 8:52:14 PM EDT
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A couple of months ago, I had an experience which taught me a lot about AR15's. It was one of those things which I wouldn't wish on anyone I liked. You know the saying: "experience is what you get when you don't get what you want." No one wants a bum AR15. And that's what I got. Like many of you, I have been hanging around AR15.com long enough to read a lot of stories about bum AR15's. Some swear at the lousy factory, the crummy dealer, or worse, blame every AR15 in existence as unreliable. As the manufacturers, dealers and builders have matured in the last few years, AR15's have become more reliable, but there are still horror stories about frustrating days at the range with a new AR. Newbies write about their new rifles jamming, and we offer advice. If you can relate to this experience, then this article is for you. The point is not to try to describe a fix for every AR15 problem. I believe the AR15 is a system which can be understood and fixed by the layman (like me.) A little understanding and perseverance can get you over the hump and lead you into AR15 bliss. Firstly, I am not a gunsmith, I'm just a gun tinkerer. I have owned two factory AR15's: one a Colt Sporter HBAR, and one a used Bushmaster carbine. Both rifles ran fine. Along the way, I got the build-it-yourself virus and went down that road. Eventually I had built five AR15's on a number of different receivers, including home-built uppers. I had relatively few problems. I had replaced a few springs here and there when I felt I needed to, but in general all my rifles were quite reliable. There's a downside to this: arrogance and complacency. Having a solid knowledge of how the AR15 works is a fine thing, but that may not prepare you for the bum rufle when it comes along. I assumed that bum rifle stories were everyone else's problem. Maybe, I thought, bum AR15's are just a legend, receding into firearm history.  Boy, was I wrong. I am not going to mention the brand name of any of the components in this bum AR15. I don't want the story to be sidetracked into vendor/dealer bashing or praising. The problems I had could happen with most any rifle. I bought a lower, parts, furniture, barrel, upper receiver and giblets. It took a while for all the parts to come together and fit my vision of what this AR should look like. When it was done, I was very happy. It just seemed like such a great combination. I took it to the range, and after the first two mags, the jamming started. Once per magazine, then twice or more per magazine, I'm having to clear jams. It was an ugly scene. I kept saying to myself "I built this rifle, and I don't build rifles that jam! What's going on?!?!?!?" And so, my harrowing journey began. Examining the failures: After the first round of messing with the rifle, chasing the typical causes of jams, and getting nowhere, I had to think more carefully about my methodology. We are used to using two terms: FTF (failure to feed) and FTE (failure to extract or eject). But you can't diagnose a problem by just saying "it jammed" or "I had a FTE!" The first thing I had to do was STOP clearing the jams! Instead of gruntin', gritting my teeth and going through the unjam-the-rifle routine, I started putting the rifle down on the bench pointing down range and just looking at the exact way the jam was happening. Here are the jams I had with my rifle:
What happens in a self-loading rifle in a few hundredths of a second is complicated, and very dependent on the force of gas, the weight of bolts and carriers, and the tension of the springs. All these affect timing. And I have begun to understand that timing is everything. I am beginning to think that one of the reasons AK's are so reliable is that they are purpose-built loose and the gas piston, rod and bolt carrier are heavy, which makes them cycle slower. The slower the action, the easier it is for everything to be in the right place when each step in the fire-unload-reload sequence occurs. I'm not a gunsmith, and I've never fired a full-auto weapon, but I would bet dollars to doughnuts that the faster a gun cycles, the more stringent the designers must be on the tolerances of the components to insure that timing is consistent. Magazines: Everyone knows that AR's need good magazines to work right. In my case, I had six known good magazines that never failed in my other rifles. One or two seemed to be okay in the bum rifle, then later they would jam as badly as the others. This bothered the crap out of me. I almost dumped a wad on new-in-wrap USGI mags just to see if they would work better. But that would leave me with a rifle which would only work with certain mags, and I didn't like that idea at all. I needed to fix the rifle, not throw away mags or use only certain mags. Swapping uppers and lowers: If you or a buddy have a known good rifle, swap the uppers and lowers and figure out which one's busted. Makes perfect sense, right? In fact, though it might narrow down the list of possible causes, sometimes it doesn't tell you much. In my case it didn't help at all. When I swapped uppers and lowers with "ol' reliable" I ended up with two rifles jamming! I had to believe that the first rifle had something like rifle influenza, and it was spreading! Maybe I needed to wipe my gun cabinet down with Lysol or something and quarantine these sickos. Actually, the jams were slightly different and it seemed like the lower had a bigger share of them. But still, I was left scratching my head. Carbines vs. rifles: Remember my little rant about timing? AR15 rifles and carbines are two different animals in some important ways. The gas pressure on a carbine (16" barrel) is much higher because the gas port is closer to the chamber. This means that they are less likely to short-stroke (meaning, the bolt doesn't come all the way back,) but they cycle sooner, faster and harder. AR15 rifles (20" barrels) work at lower pressure, have a heavier buffer, and a longer spring. The distance that the bolt and carrier must travel is the same for a rifle and a carbine, but the amount of gas pressure, the weight of the buffer and the strength of the action (recoil) spring are very different. The designers of the first carbine-length M16 didn't just chop here and squeeze there. They had to keep the cycle time about the same as a rifle by adjusting the strength of the spring as well as it's length, to work correctly with a shorter and lighter buffer, and higher gas pressure that hits sooner. All of my rifles to this point had rifle-length buffers and springs, and carbine-length barrels. I think that the slower/heavier buffer combined with the higher pressure makes this combination more reliable than others (JMHO, YMMV). But this new bum carbine had a carbine-length spring and buffer, with a 16" barrel. So I spent a lot of time thinking about how the timing was faster and how this could be causing the jams. ...And repeat: My diagnosis of the problems didn't take one or two trips to the range. I believe I ended up making five trips, and using about 800 rounds of ammo, to work the bugs out. I went through the swap-uppers-and-lowers trick twice along the way. And I sorted through my magazines and kept working with the jammers. Every step of the way things got a little bit better. One type of jam would go away, then another, as I tried different fixes. Unfortunately, one change I made seemed to make things worse, which only goes to show you that the AR15 is a system, and changing one thing can have unforeseen effects in other areas. Sending it back to the factory: Some of you are asking "why don't you just send it back to the manufacturer?" Good question. In fact, I did send the lower back, and the factory replaced it. I had convinced myself that the jams were happening because the magazine catch was slightly off and the mags were wiggling too much. When I got the lower back and reassembled it, the jams were just as bad as ever. If you have a factory gun and it's jamming or otherwise behaving badly, then go right ahead and send it back. In my case, I built the gun, so somehow, something I did or some part I used was causing the problem. It was my bum rifle, therefore I must be the bum that screwed it up, and I had to be the bum that would fix it. Extractor spring: When you looked down the list of jams above you probably spotted the one where the extractor failed to extract the case. That's easy to fix! Just put in a new extractor spring. Well, I have a little bag of Wolff extra power extractor springs for just such occasions. But it made little difference. A few less failures to extract, but they were still happening. Any improvement is better than the status quo, so it's worth it, and wasn't hard to do. Feed ramp: When I disassembled the bum rifle after the first range jam session, I noticed that there were small copper-colored marks just below the feed ramps. I always polish the ramps with 400 grit emery before assembly, but now I needed to go further. If it works for Colt, it can work for me. I carefully dremelled the feedramps about 3/32" lower, so that the lower edge is below the barrel extension, into the receiver itself. I was careful to keep the angle and shape as close to original as possible. Again I polished the newly lowered ramps smooth as a baby's bottom, and all sharp angles were softly rounded. This resulted in more improvement. Still enough jams to make me pull my hair (what's left of it) out, but we're making progress. Buffer: One of the things that bothered me was that sometimes the bolt was catching the side of the case and jamming. I began to cogitate on this. It seemed to me that the only way this could happen is if the bolt was coming forward before that magazine spring had pushed the cartridge completely up to the feed lips of the magazine. But it only happened with some magazines, and I had replaced the springs on some of my magazines a while back. I'm reluctant to blame the magazines, especially when I know they work in my other AR's. Then I remembered about these strange things called "H buffers" for carbines. I remember reading that the extra weight of an H buffer makes it cycle more slowly. So I dutifully went to the Web page of a dealer that had real Colt H buffers, and had one in my grubby hands a few days later. You can guess the effect, right? Improvement! But not completely fixed  . I still had those same side-jams, but fewer of them. I'm getting to one jam per mag... not good, but not as bad as it was.Action (recoil) spring: I went back to thinking about the timing of the bolt coming forward. A stronger action spring might help slow the cycle time by slowing the bolt and carrier as they move to the rear. It bugged me that in some cases the bolt just didn't have the oomph to push the cartridge out of the magazine. Also, it seemed to me that if the action spring wasn't driving the bolt forward hard enough, the extractor might not be able to grab the rim of the case. Obviously the action spring needed attention. I had got the action spring of the bum gun when I had previously purchased a M4 stock for cheap. I had sold the stock but kept the cheap spring and buffer. Go to Wolff springs Web site: extra power carbine action spring, on the way. Big improvement. No more extraction problems. One nasty side effect: those jams which had the cartridge cockeyed between the mag and the chamber mouth were fewer but worse. When one of those jams happened, the cartridges were getting mangled, so mangled they wouldn't chamber. Happily, this didn't happen often, but often enough to keep me on the hunt. Magazines revisited: With a stiffer action spring and an H buffer, the cycle time is as slow as I can get it without installing a non-standard gas tube to soften the gas pressure. If the bolt is still catching the side of the cartridge, then a stiffer magazine spring might be needed to push the cartridge up faster. I broke down and bought a 10-pack of extra power mag springs from Wolff (by now the Wolff order lady recognizes my voice; shouldn't I get a volume discount?) I cleaned the inside of each magazine as I examined the springs, replacing the ones which looked weak. I didn't want anything to keep those cartridges from snapping to the top. That did it. Next trip to the range, I am consistently getting through every mag with no jams. Life is good. I am now thinking of the subject AR15 carbine as not so much a bum, but a problem child. The future looks bright, and I am willing to let bygones be bygones. Breaking it in: I have in the past advised newbies to just keep clearing jams for 300 rounds during break-in, and the new AR15 will get more reliable as the parts wear-in. Maybe while I was swapping out all these parts, the bum rifle was just breaking in? Maybe. I still think the kind of jams I was getting were extreme, and not the kind of thing you get with a new AR (like short-stroking.) I do expect that this rifle will get to the place where I can be absolutely confident it will go bang and cycle every time with no jams. I just need to keep shooting it. This was a painful and ugly process. My rifle is a bum no more, and that ain't too shabby. The biggest lesson to me was don't give up. Since I had no where else to turn, I was forced to keep going through a mental movie of my AR15 cycling. It came back to timing: springs, weights and gas pressure. Everything being in the right place at the right time. Keep these things in mind if you buy or build a bum AR15. You can fix it, but you have to think, be methodical, and keep at it. C_M |
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Nice write up. I am in the mist of putting my first AR together. Hope it turns out slightly better. Like you said AK's are reliable. I have not had one single jam in my MAK90 no matter what mag or what ammo I use. That is one reason I will always have it around. |
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