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Posted: 12/23/2007 12:29:28 AM EDT
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Sounds more like low feeds from either the ammo not loaded right (can be too hot causing over function/too weak causing short stroking, which is acts the same as over functioning) or something just not right with the mag alignment in the lower receiver to the upper receiver. To start off, scrub/clean the hell out of the chamber with a chamber brush by hand. Armalite chambers their barrels a little on the tight side, so the problem could be just a bit of chamber fouling that you are missing while cleaning. While you have the CLP out to lube the upper bearing surfaces of the rifle after cleaning, pull the mags apart and give than a good cleaning as well (just use CLP to do this). From there, perform a live cycle test with your reloads, which is to load a single round into the mag, charge and fire, with the correct end result being that the bolt is locked back on the catch. If the rifle passes this test, the check the mag catch button threaded section to confirm that it’s flush with the face of the button. From there, with a empty mag, push in on the mag release button and see how much father up the mag well you can get the mag to rise before it’s lips bottom out on the bottom of the closed carrier (best down when cleaning the mags/have them apart since you don’t have to fight the follower). You should be able to push up the mag about ¼”, but if you find that it’s going much more than this, then either the mag catch retaining shelf was milled a bit low/mag catch location in the receiver milled too low, or the upper to lower has too much of a gap between them and the mag is not being help up high enough for a clean feed. Note: since this is a new problem and not something that happened from the start (unless the mags are now just loose as hell in the mag well, I think that you are going to find the problem with either the reloads, or a cleaning issue. Regarding the two lines on the bullets, are they being caused by end burs on the ramps, or are the ramps just chatter city from when they were milled. Bullet setback will not come from the bullet (tip) scrapping up the feed ramps or end bur catching them, but will come from the bullet first striking the upper receiver below the feed ramps, then being driven forward into the ramps/chamber after the bullet has been set back. Hell to be blunt, I don’t even crimp with it comes to target loads for rapids, and haven’t had a problem with bullet set back. Granted that I have tweaked my dies to make dam sure that the ID sizing button keeps the case neck .003 under sized for a tight bullet tension, but if you are under OAL trimming the case, this could be the problem as well (not enough next tension to hold the bullet, FCD crimp or not. |
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Thanks for reply Dano253 The one round test had no problems. Bolt locked back every time. The mags appear to be seated to the right height. Here's picture showing the hang up at the locking lugs. You can see, the corner of the lug digging into the bullet. In this case the hang up usually happens with the round on the right side of the mag. http://i256.photobucket.com/albums/hh198/uncle_walty/PC300178.jpg Here's picture showing nicks on the bullet. There is same nick on the other side of the bullet. http://i256.photobucket.com/albums/hh198/uncle_walty/PC300176.jpg Any more suggestions appreciated. Are the lug corners sharper than usual? |
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Here's a picture that shows the breech and feed ramps and relative position of the mag. The right side round sometimes pops up like this when I pull the charging handle back slowly to not eject the chambered round too far away. Of course it doesn't jam against the locking lug like this. When I pull the CH back quickly the round stays under the mag lip. The left side always stays under the mag lip no matter how fast or slow I manual charge. The copper on the feed ramp is just from the manual charging. http://i256.photobucket.com/albums/hh198/uncle_walty/PC300174.jpg |
I need a few more photos of the upper feed ramp areas from the back of the receiver (read shotgun it open and take the photo) So I can compare them to a Colt M-4 barrel extension with extended ramps and the upper receiver area since your appears to be ramps as well. Also I want to see the alignment of the upper and barrel extension ramps against the center of the front take down lug as well.
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Here's a shot from under the upper http://i256.photobucket.com/albums/hh198/uncle_walty/P1010214.jpg Here's a shot from back of upper http://i256.photobucket.com/albums/hh198/uncle_walty/P1010216.jpg Here's the results of bullet set back. On the round with the bullet nick, the top of the round relative to the mag is at the top of the picture so you can orient the angle of the nick. http://i256.photobucket.com/albums/hh198/uncle_walty/P1010219.jpg Here's a shot of a jam from the left side of mag. http://i256.photobucket.com/albums/hh198/uncle_walty/P1010211.jpg I'm getting this jam from both sides of the mag now. Seems like some mags tend to jam more one side than the other. I've gotten these same jams with a new 20" Armalite upper that I haven't shot yet using the same lower. Although the 20' upper haven't set back the bullet when I charge a second time. I'm going to build my second lower and see if there is a difference. I get more jams with the Yugo bullets than Winchester and Hornady but that maybe the Ygo rounds are pretty nicked up now. Even rounds that do not jam get nicks on the bullet most of the time. With those locking lugs there just pass the feed ramp, I can't see how the bullet can avoid being nicked unless the bullet comes in at more of an angle and rides over the lugs. Are these nicks on the bullets common since the feed ramps and lugs on these two Armalite uppers looks normal to my untrained eyes comparing to photos I've found. You know I never had feed problems with my mini-14.have Thanks for your help Dano. |
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1. The barrel extension (barrel) is not indexed correctly (installed center of the upper). The center of the feed ramps should be dead center of the front lug. This will align the barrel extension feed ramps center of the upper extended feed ramps as well. 2. The upper receiver extended ramps end edges should be slightly proud/higher of the barrel extension feed ramps start points (where they come together. On your upper, this in not the case (backwards) and the markings on the entry point of the barrel extension ramps tell the tail. Simply instead of the bullet tip riding the upper ramps and slipping over a slight drop between the barrel extension ramps, your upper/barrel ramps has an rise/upward step between the two and the reason for the setback and failures to feed (bullet gets slow down before even making it to the end of the ramps. Not sure who put the upper together, but at this point, the barrel needs to be pulled and the barrel extension feed ramps need to be remilled (or just the beginings of the barrel ramps be addres to lower then slightly below the end of the upper's extended ramps where they meet). Also with the barrel off, take a stone to the end of the ramps and de-bur them a bit (at the tips/tops of the U-cut sections in the feed ramps that have sharp end burs). |
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Thanks Dano. I never would have noticed those problems with the upper. The upper is a complete Armalite upper (U15A4CB) I bought from Armalite in April 2007. I'll have to give Armalite a call about this upper. Would it be okay with you if I reference your evaluation of the upper in my correspondence with Armalite? Is it possible the barrel extension could have loosen and moved during shooting? With everything lined up (typical AR), will the bullet ride up above the locking lugs pass the ramps or does the bullet still hit the lugs but not at an angle that would pinch and jam? If the latter, will the bullets still be nicked but not as bad as my examples? |
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