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Posted: 4/6/2010 11:56:46 PM EDT
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I recently put together a dedicated 3-gun rifle and had some major double feed issues at the first big match I used it in. I had probably put around 500 rounds through it beforehand without any problems and took it to a two-day 3-gun match a couple weekends back. Halfway through the first day, the rifle tried to feed two rounds into the chamber at once at the end of a stage. I thought maybe it was too dirty, so I cleaned it and continued on. On the second day, it started doing it the same thing again at the beginning of a stage (45 round stage), and it got progressively more frequent throughout the stage until it was double feeding almost every round. Thinking it was a mag issue, I had switched to a fresh mag halfway through that stage, but the problem continued with the new mag. Each time, it was trying to feed two live rounds into the chamber at once. The first round would be correctly positioned but get stuck when the bolt caught the middle of the second round and tried to force it into the chamber as well. This happened with three different PMAGs that have all worked flawlessly in other rifles, and in this rifle previously. Afterward, I noticed that the double feeds only happened when I was prone using the magazine as a monopod. I've never had a problem monopoding off the mag, especially with PMAGS, and I find it very useful in 3-gun since bipods aren't allowed. I don't know if using the mag as a monopod is the source of the problem or just a coincidence (plan on testing it further at the range later this week). Either way, a rifle should be able function reliably while resting in the mag IMO. I'm usually pretty good at diagnosing AR malfunctions, but feeding two live rounds is a new one on me. The rifle uses an 18" barrel, rifle gas system, rifle stock, and standard BCG. I was shooting Hornady 75 grain ammo. Here's a pic of the rifle:  |
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I would check how much play is in the mag in the up/down direction. It could be that the mag catch is undersize, or the mag locking cut is oversize, allowing the mag to go too high in the receiver when it is pushed upward while resting it on the ground. I wouldn't think the BCG could reach that far into the mag, but I guess it is possible
Try putting the mag into the gun, with the bolt locked to the rear, and try to move the mag up and down. If there is excessive movement, see if there is any obvious cause (mag catch moving in its recess in the lower, etc. Are you using lacquer coated rounds? I guess they could start to stick together, causing 2 to strip out at a time. Sorry, just throwing things against the wall to see if one sticks. |
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Quoted:
In the Army were always told not to let the magazine rest on the ground because it may cause malfunctions. I think that may be your problem. Yep, mag is forced upwards/canted in the well, and creates the wrong angle of attack for both the bolt stripping the round, and the round coming out of the mag. Best advice is you are not going to use a bipod, then get a sling and sling up tight in the prone position with your elbow being the tripod. |
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Quoted: In the Army were always told not to let the magazine rest on the ground because it may cause malfunctions. I think that may be your problem. And arfcom told me they were wrong.  Actually, I've had instructors with both Tiger Valley and Magpul Dynamics say that the rifle should be capable of shooting off the mag in classes I've taken with them. However, it does seem to be causing the issue here. I'm going to the range tomorrow for more testing. The mag does not seem to go further up into the receiver than any of my other ARs. I've using a rifle buffer and spring, so I don't really have any choice on buffers. Slinging up works great for Highpower, but I don't have time in 3-gun. |
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Went to the range today, but couldn't get the rifle to malfunction again. Using the mag as a monopod (same mags I had trouble with), I tried pushing down, down and forward, down and back, everything including pulling back on the mag with my off hand. Shouldn't come as a surprise though––my guns only malfunction during matches. |
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