I’ve got an AR-15 (my own) that has had maybe 5-600 rounds fired through it. Had a problem since day one. I started out with cheap ammo (epoxy-coated steel case). I know a lot of guys don’t like to shoot that, but I like to shoot, and the good stuff is expensive. I could shoot maybe 15-20 rounds, and I would start having feeding problems. Disassemble, clean, same thing. It extracts, but doesn’t feed the next round. It cycles enough to cock the trigger, but not enough to pick up the next round. Blamed the ammo. Figured the barrel was heating up and the epoxy on the cases was sticking. Tried better ammo. Ran an experiment that covered it all. 5.56, .223, 55 grain, 62 grain, different brands, different types and brands of magazines. Threw in a dozen different variables. The better ammo helped. Now I can fire 40-50 rounds before the problem re-occurs.
I can only assume it is a gas problem, because everything works fine initially. What I don’t understand is what’s changing. I can clean the chamber/bore and BCA, but have not cleaned or removed the gas tube. Why then does it operate fine at first and then go downhill? If it was a problem with the gas tube, I would expect it to still be that way after cleaning the rest of the gun. And like I said, the problem has been there since day one, so I can’t see it being any kind of build-up in the tube. What would cause it to operate fine, and then start losing pressure?
I am new to this, and am still on the Pistolsmithing section of my AGI course, so I don’t claim to be proficient at all. I did however, get the armorers course for the AR-15 before I even enrolled with AGI, and have watched many on-line videos pertaining to it as well. I have not come across a similar situation anywhere. Any advice would be appreciated. Sam
Question Follow Up
More info. I’ll also point out that I wouldn’t waste your guys’ time without doing my due diligence. I searched the forum and read every thread I could find pertaining to AR-15’s. While I found several similar problems, they all had one thing in common-they were consistent. The problem I am having is progressive. Starts off fine and gets worse and worse. I have also experimented with lubrication. Everything from Rem-Oil to Hoppe’s High Viscosity Lubricating Oil. Applications from light to heavy. Checked the gas key screws-tight and staked. Checked the rings and did all the common “tests”. Considered buffer and spring, but again, the problem is progressive. It has nothing to with extraction-I’ve only had one failure to extract since I’ve owned the gun and that I DO write off to the epoxy coated ammo sticking. Pulled the rim off the case and I had to get the case out when I got home from the range. Lesson learned. Steel cased ammo will never darken my chamber again.
Point is while I’m a novice to gunsmithing, I’m not a novice to guns. I’ve been around them all my life and own… many. I’m just not that familiar with the AR-15. Checked everything I can think of. The ONLY reason I haven’t pulled the gas tube is because I’m afraid I’ll bend it or bitch it up and have to wait a week and a half for a new one to come in the mail. Patience is not one of my many virtues. Funny part is, I bought the gun because it is the one type I am the LEAST familiar with and it’s the only one I’ve ever had problems with. I’ll damn sure be familiar with it when I get through, but that’s the whole reason I signed up for the AGI Level I course. (Plan to take II and III later, just pacing myself financially) I refuse to take it to a gunsmith when I’m studying to be one. I’m not going to let it stump me and I’d appreciate your advice. Sam
As you can clean the chamber and get a temporary fix of the problem, I would polish the chamber with 600 grit paper after a good cleaning. I would also check the extractor. DC
Question Follow Up
Appreciate the input. Polishing the chamber sounds like a no-lose proposition, but what exactly should I be checking the extractor FOR. I’ve got a good positive angle, it’s not chipped or damaged, and it is extracting (and ejecting) just fine. The case that had the rim pulled off was a while back, (probably 200 rounds ago) and I’ve checked the extractor for damage every time I’ve had it apart since. Is there something else I need to look for? Sam
Answer
Hey Sam,
I would clean the bolt and chamber with simple Green as shown in the Armor courses. Place some oil / lube after. Are there any marks or scratches on the fired case? Polish the chamber with 360 grit or 400 grit 600 grit up to 800 grit after this maybe use some polishing compound too. Make it look like a mirror. (Extractor) Make sure that the hook is Positive. Take the bolt out the gun remove the firing pin and ejector from the bolt. Place a round on the bolt face under the extractor. This is the Extractor Bolt test. Wave the bolt around check to see if it falls off. If it does the Extractor needs to be fitted. The extractor should hold the round on the face of the bolt. Have you check to see if the extractor is broke, clacked or broken? Check the spring out on the Extractor.
Let us know what you find….Tony
Answer
Is this a carbine, mid or rifle length gas system? First step would be to polish the chamber as others have said. -pj
Question Follow Up
It’s a carbine. Polishing the chamber seems to be the consensus all around. Gonna tear it back down in the morning. Follow the other tips too. Thanks guys. I had convinced myself it was a gas problem, just couldn’t figure out HOW it was a gas problem. From what I’m gathering you guys are saying it’s working TOO HARD to extract, causing it to short cycle? Sam
Answer
It still can be a gas problem, carbines are noted to be fussy .You may need to increase gas port. Let us know if polishing the chamber helped. -pj
Question Follow Up
Will do. Put it on hold for a few days. I decided “in for a penny, in for a pound”. I was going to half-ass the polishing with some coat hanger wire and sandpaper in a cordless drill. I’ve had a Foredom tool on my wish-list since I signed up for the course, but didn’t want to spring for it until I really needed it. My wife decided to buy me one for my birthday. Love that woman. (By the way – I had to buy it in pieces, but I found everything through Amazon for $200. Would’ve cost $350 from Brownell’s for the exact same outfit.) Decided to wait and tear the rascal all the way down (gas tube too) and make a serious project out of it, soon as the UPS man comes. So far all I have done is watch videos and take things apart and put them back together for familiarity, but if I’m going to make a go of this, it’s time to get serious. Ordered a torque wrench, AR multipurpose wrench, gonna tear it all to pieces. At least if the tips you guys have given me don’t work, I won’t be hesitant to tear back into it to try something else.
Watched the Tech-tip on chamber polishing from Guntech DVD #77. I’ve got to say, GCA is a hell of a resource. Member for life. I’ve found Disassembly/Reassembly videos for every gun I own on here. I appreciate all the tips, and I will let you know how it goes. Gonna focus on the Pistolsmithing course until my stuff gets here. I’m more familiar with those. If we get invaded before I get the AR right, I’ll just have to wait for ’em to get closer to me. Sam
Answer
So she short cycles…..fires extracts and ejects, recocks but doesn’t move back far enough to load a round from the magazine. By all means tear it completely down to learn. Not sure you need to for curing this issue. Polish the chamber like others said. I would start with 320 grit then 400 then 500 last. If you want to go to a finer/higher grit you can it wouldn’t be a problem.
Check to make sure the ejector is fitted correctly….extends as far as it can and not interfere with feeding live rounds from the magazine. Then onto the extractor, make the extractor hook positive in the working position. Make sure the extractor hook holds the case as close to the bolt face as it can and still snap over the rim of the shells…..this is something that is a common problem on AR’s. The extractor and ejector fitting shouldn’t have anything to do with short cycling but will help the gun function better/correctly and cure any other potential issues that may arise. You may have to adjust the gas system but would do that as a last resort if the chamber and other work doesn’t cure your issues. Ken
Comment from Mark Foster
Here’s my trouble-shooting list for short cycling. It’s generally NOT a rough chamber or extractor issue.
Yes, the choice of ammo was initially bad and may still be causing him problems. Don’t be afraid to take off the gas tube – a new one costs under $12 from Brownells and the .081 diameter x ¼” long roll pins are available at many good hardware stores for 5 cents ($1.00 from Brownells!). I buy them in bulk from McMaster-Carr.
He has checked most of the following list. Because items 1 and 2 were definite, I think there is a possibility that the gas tube is clogged. He should NOT attempt to use pipe cleaners to clean it – that usually makes it worse. Before replacing the gas tube, he should try items 3-6 first, then if those aren’t the problem, go on to replace the gas tube. Less than 5 minutes to change it for a novice – 2-3 minutes for someone experienced.
Some chance it is magazine related. Don’t be cheap and use GI magazines that are defective. It is a slim chance but a possibility. Also a slim chance that it is gas port related, since he is getting 15-20 good rounds and then a problem. That said, things can get worse after heating up, such as the carrier key, carrier key screws, etc.
| Problem | Potential Cause | Solution |
| Short Cycle / Short Stroke | 1. Defective Ammunition | 1. Use new U.S. factory made commercial or Mil-spec brass cased ammunition. Check for damaged cases |
| 2. Dirty Chamber | 2. Clean chamber with chamber brush and cleaning solution, wipe dry and inspect for debris or damage | |
| 3. Loose Carrier Key | 3. Remove bolt carrier group, clean all parts, remove any oil under the carrier key. Reinstall screws and torque to 35-40 inch-pounds. Double stake the screws | |
| 4. Broken Carrier Key Screws | 4. Replace screws as above | |
| 5. Worn Carrier Key | 5. Replace carrier key | |
| 6. Bent or Worn Gas Rings | 6. Replace gas rings | |
| 7. Bent, Worn or clogged Gas Tube | 7. Realign gas tube or replace gas tube | |
| 8. Gas Port in Barrel and Port in Gas Block or Front Sight misaligned. | 8. Carefully expand the gas block / front sight hole (not the barrel!) with a Dremel tool. Drift port hole in the direction of the barrel hole to create a “channel” for the gas | |
| 9. Improper Gas Port Size | 9. Check gas port size, carefully drill larger if undersize | |
| 10. Bent Lips on Magazine (causing bolt drag) | 10. Replace magazine. (destroy old magazine) | |
| 11. N/A | ||
| 12. Improper Buffer or Spring | 12. Replace with proper buffer or spring (rifle spring has 42 coils – CAR has 37 coils) | |
Mark
