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Posted: 9/19/2010 11:15:25 AM EDT
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I have a pair of mid-length lightweight uppers that I purchased from a reputable manufacturer during the height of the 2008-2009 buying frenzy. Neither has worked reliably.
I get horrendous double feeds in both. The empties are being extracted but not ejected. They will sometimes lodge themselves with the case head stuck over and in front of the bolt. This isn't an easy one to clear  There isn't a clear pattern as to when this happens. Sometimes it will happen right away when the rifle is clean, and other times it will wait for a mag or two or three... Sometimes it gets warmed up and will spit out 3 or 4 mags rapid fire without a hitch. I thought this was a break in issue, but I've got about 500-700 rounds through each with no sign of a fix.
The last time I was at the range I switched my dept. issued bushy carrier group (lighter AR15 carrier) and managed to fire about 200 rounds with no problems. This was promising but not completely convincing as these rifles have done that before. I tried combinations of the bushy carrier with the rifle's bolt and vise versa, but neither worked without malfs. Some particulars: Pencil barrel mid length KISS carbines. I love this configuration. Nothing fancy. Standard FSB (seems very securely attached to bbl), standard handguards, etc... M16 carriers Gas keys are staked and secure. The fit of the bolt inside the carrier seems a little sloppy to me, but I can set the carrier on the bolt without it collapsing. The ejectors are just a bit shorter than my bushy. They aren't quite flush with the bolt lugs. Normal weight carbine buffers. Mil spec carbine receiver extension. Staked castle nut. The gas tubes are tight at the FSB, but wiggle at the barrel nut/upper receiver. My bushy doesn't do this. Federal XM193 and Winchester Q3131A ammo. My concerns: 1. Loose gas tubes. Is this normal? If not, what is the likely cause? Out of spec gas tube, barrel nut, upper? 2. Is an M16 carrier too heavy for a middy? I wouldn't think so, since they use them in rifle length systems, but since the bushy BCG worked it has me wondering. 3. Ejectors shorter than normal. I'm hoping this is something I can figure out without having to send them back to the manufacturer. Thanks |
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Well every double feed problem that I have ever had was mag related and nothing to do with the weapon. The failure to eject could be several things .... weak extractor spring dropping the case before ejection .... or ejector binding up in it's channel .... or even an over gassed rifle and the "jarring hit" of the extra gas on the BCG is pulling the extractor off the case (but that usually leaves the case in the chamber .. but not always).
Test the ejector with a spent case ... as long as the ejector is moving freely in it's channel then it working. Not sure why your gas tube is loose unless it wasn't aligned properly with the gas key and it's taken a hit or two from the BCG? ... take the bolt out of the carrier and slide the carrier into the upper ... does the key on the carrier align with the gas tube in the upper? if there is any binding there it needs to be corrected (new one probably would be prudent). I probably would also do the BCM SOPMOD upgrade kit on the extractor. |
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Quoted:
Ejector moves freely. As far as mags I've only used 20 and 30 round Pmags in it. They seem to work fine in my bushy. Gas tube and gas key seem to align fine. I'm wondering if the slop is causing random misalignment. Could be causing drag on the BCG if it's not lining up sometimes and definitely could be a contributor to the problems .. it shouldn't be loose .. could be the tube itself .. the roll pin holding it in the GB .. or even an out of spec GB. I would try a new tube and roll pin .. if that doesn't work then the GB hole for the tube is over sized. |
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