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Posted: 4/25/2007 5:52:07 PM EDT
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Hey guys, I took my AR to the range with a new (to me) upper recently and had a pretty consistent FTF prob with it. The round is impacting below the feed ramps and not entering the chamber. The bullet actually hits hard enough to drive it half way back into the case. When this occurs the bolt is behind the bullet which leads me to believe that it's cycling right, but something's preventing the bullet from coming up in the front high enough to enter the chamber. So far I've tried 4 different magazines and 2 different kinds of ammo all with the same problem. TIA, Dave |
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Thanks for the reply. Even though I've used the m-16/ar-15 platform for years, keep in mind I'm a complete newb when it comes to the mechanics of the rifle. (Something I hope to remedy) With that in mind I ask how does one tighten the mag catch? Edited to add: If I remember correctly the rounds were impacting on the black part of the upper just below the grooves. Here's a pic of my chamber: http://dotsun.homeip.net/KIF_0614.jpg |
| Try jaming a piece of cardboard in back of the mag at the bottom of the mag well. This will tilt the mag slightly and the difference in the mag feed angle may be all you need. If this corrects the problem then i would pry out the back spot welded seam on the mags toward the bottom of the mag well so as to copie what you did by jaming the cardboard in it. Simpler then trying to realign the mag lips. |
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I'll give the cardboard test a shot the next time I get to the range. I just tried to turn the mag catch, but it doesn't seem to be able to clear the bolt release no matter what I do. hinking.gif Thanks again for the replies, if you think of anything else I'm game. Someone suggested I take a dremel and polish the feed ramps, but I'm not sure I trust myself doing that just yet. :) |
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Drive the pin out with a roll pin punch, replace it the same way afterwards. The bolt catch does not have to be removed in order to adjust or remove the mag catch. With the mag button fully pushed into the receiver (beyond flush), the mag catch will clear the bolt catch lever. Dano523 |
I never have a problem with that...sometimes the mag catch is the last part I put in when I'm building lowers. oh well. |
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Short stroking can cause some low feedings out of the mags. The cause and effect is the weak cycle does not cause the strong buffer to back of the receiver extension, leading to lack/lessened dead blow effect of the buffer, and the mag does not get the extra B/C stall time, nor the assisting jarring to get the top round in the mag back into position for a clean strip. Here in regards to a short stroking test, confirm that the bolt is locking back on the last fire round out of the mag. Also, on this note, proper cleaning, and CLP lubing is a must, and if needed, a quick search of the Maintenance & Cleaning forum will direct you on how to achieve both. Next confirm that the mag catch threaded section is flush with the release button. As noted, push the release button all the way in with something like a pencil releaser, and turn the catch the needed turns to flush out the thread catch section with the face of the button. If you find that you can only get the threaded section 1/2 in or out when correctly indexed with the receiver slot, the spin the button 90* and reinstall the catch. Mag conditions can have a hand in low feeding as well. On new mags, you may have to break the in by hand to allow them to clean feed. Here, you use a wooden ruler to push all the way down on the follower, then it to snap back under spring tension alone. Do this about 20 times per mag to allow the follower to mate into the inside of the body, then pull the mags down and give them a good cleaning. If just an older mag with a good working spring, then cleaning the mag with CLP alone may solve the problem as well. Lastly, some rifles may have a problem with some bullet designs. In regards to known bullet type, HP can be a problem, and in regards to Win 45G HP ammo, not only will the tip cause a problem, but the round is loaded outside of the normal pressure spike duration of the AR type ammo's, with jamming almost a constant problem on some rigs. M-4 ramping was design to allow the rifle to digest more off- standard military ammo type offerings, so in regards to allowing the rifle up to accept more special purpose ammo types, that is an option, but again as stated, there will be some types of factory ammos offered that were just never designed to work in the rifles (power spike/dwell rate). P.S. Welcome to the site!!! |
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How big is the gap between your upper and lower. There should be enough of a gap to see daylight through, but only barely. Don't have anything to go off right now, but the gap should probably not be more than 0.02 inches. If it is more than this, it may be an out of spec upper or lower. Very small chance of this being the case, but it happens with some of the cheaper part vendors out there. Otherwise, as usual, Dano covered everything else. You said you used differnet mags, make sure a couple of those are fairly new usgi mags, just to verify that you are not dealing with old worn out springs coupled with weak ammo. |
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I just checked, and their is no gap at all between the U/L. Yeah I'm hoping it's the mags although it seems unlikely that I have 4 bad. I'll know more when I can try out my buds mags and vice versa. :) Edited to add: I still can't get the mag catch to turn past the bolt catch. I pushed it in as far as it would physically go, but it won't clear no matter how hard I try. |
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UPDATE: I took my ar and a friend's to the range today. Results: 1. We first tried his mags in my rifle, ftf. 2. Swapped my complete upper onto his lower, ftf. 3. Put his bolt/bolt carrier in my upper that was still on his lower, ftf. Conclusion: It's the upper! (I'm quick like that) At this point, I plan on checking the gas tube and if all looks ok there, the only other thing that I can think of is to polish those feed ramps. having edited for spelling |
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I don't think that is necessary, two of my rifles with which I have never had a problem do not have M4 feed ramps. Its too bad you're not in AZ, I'd like to take a look at it. Have you posted in the TN hometown forum? someone might be able to help you. edit: what is the brand of the upper? |
1. 4 different types of ammo, 2 were mil surplus, 1 was WWB, 1 was Rem. All 55gr FMJ. 2. Oly Arms lower, I haven't been able to identify any markings on the upper. Any idea where to look for that? 3. 5 different mags, I'd have to look at my 4 to see the brand. The 5th was my friend's mag and was working perfectly in his rifle. Hard to believe that could be the cause at this point. |
I only found this on the whole upper: http://dotsun.homeip.net/ar1.jpg And while I was taking pics, I just couldn't stop: :) http://dotsun.homeip.net/ar2.jpg http://dotsun.homeip.net/ar3.jpg |
dude your barrel extention is crooked as hell, its twisted in the receiver. thats your problem. 
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Try the upper on another Lower receiver, If the upper runs on another receiver, pull the mag catch out of the working lower, and try it in your lower. Also as pointed out, the barrel is not indexed correctly on your upper receiver, and as stated a while back, could be causing lug binding on ejection, leading to semi short stroking (remember the whole buffer jolting effect). |
I tried the upper on another lower as posted above in my recent range report. :) It didn't run at all. So the barrel is twisted? How can you tell and how do I fix it? |
| look at the right feedramp, its almost inline with the receiver lug. now look at the left feedramp its higher up and not inline with the receiver lug. check to see if the barrel is tight, check to see if the notch in the upper receiver that excepts the receiver extention pin is centered and not sloppy, also check and make sure there is a pin in the receiver extention. with it being crooked like that the bullets dont have a straight patch to travel in, the bolt may have a hard time aligning, also the gas tube may not align either. which may also mean your front sight is canted as well. |
Ok, being a complete newb at gunsmithing :) you're saying that the feed ramps in A are rotated too far clockwise in the pic in relation to B? I thought it might be the pic angle, but after looking at it, it does indeed appear to be a bit off. BTW, I really appreciate all the comments and suggestions that everyone has posted for me. http://dotsun.homeip.net/ar8.jpg |
| if you really look close, on the edge of the receiver you can see where the tips of the bullets have been hitting, thats where your feedramps should be lining up. it also does appear that your bullets are entering the feedramps a bit low, they shouldnt be hitting the receiver like that. |
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Update: Against all that's holy, I took a dremel to my rifle and lowered the feed ramps a bit. That has solved my feeding issues! hanks Now that the rifle feeds reliably, my second problem is much more of an issue. I occasionally get a dimpled primer but no bang. It does this with several different brands of ammo and with 2 different firing pins. Any ideas on what could be causing this? Oh, and yes it was doing this before I started my dremel work. |
first thing to do is to get a firing pin protrusion gauge and check to see how far it comes out. try that first. sometimes primmers are hard, and sometimes a triggers pull weight is so light it doesnt strike the primmer hard enough. that a few things to check out. |
Thanks for all the suggestions, guys.
 I would love to know what company built this upper.Instead of dremeling random grooves in your barrel extension, you should have had the upper fixed. It wouldn't have cost more than $40. But you knew that. There are more experienced folks here who may be able to describe this better, but your bolt is not going to lock up right with those wack-ass lugs. The difference between an open bolt and a bolt correctly rotated and locked in battery is only around 23 degrees, and you're off by at least 5. Is your front sight base canted to the right? Did you have to crank the rear sight all the way to the left to get on target? I'm surprised the gas tube isn't causing problems as well. The feeding issues are only 1 symptom of a problem that would not have been expensive to fix. |
I haven't had a chance to zero it yet, but the FSB doesn't look to me like it's canted in the least. I'll know more when I get it on some paper, but at the moment it just seems to be shooting a bit high. It seems to lock up pretty smoothly, despite my wack-ass lugs and no I didn't know it'd only cost $40 to fix 'correctly'. The last gun I took to a gunsmith didn't work any better then when I took it to him and was around $125. My 'random' dremel job was free and has certainly corrected the problem. And yes, I'd love to know who built this POS upper as well, but unless someone can identify it from my pics I'm afraid that's just a pipe dream. If anyone needs any random dremel work done, just send me a pm. |
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If you are experiencing no more problems and the gun performs to your satisfaction then just shoot it and enjoy it. Ar15barrels.com will tear down and re-assemble an upper for $40 here, though this fee is usually charged in the course of other work. He has a good reputation on the board and his own forum in the Industry section. http://tinyurl.com/yracnp If the front sight is NOT canted as the upper is now built, it sure would be if the barrel were correctly positioned. In that case it would require more work than $40 to get the whole thing in order. I'd just keep an eye on the bolt that it was wearing evenly. If only half the locking surface of the bolt lugs is shiny and the other half still retains its finish, the system will require more work. Have you checked under the handguards for any markings? |
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