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Posted: 10/2/2011 9:38:24 AM EDT
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I own a Sendra M-16A2 with a 20" bbl on it, went to shoot it yesterday and had shot 6-30 round loaded magazines with three year old Wolf ammo. Run 100%. Than, just like on and off, I went to shot, a round went off, ejected the case but did not have enough energy to cause the bolt to go back enough to push another round up and in. This happen a few times as wall as a few (seperate) rounds cases remained in the chamber. Had to use a cleaning rod to remove. This happened like 8 times in a row. I kept thinking, thinking, thinking. There was a guy at the range who had his AR and so I asked if we could trade ammo. No problem, went to shoot his brass .223, 100% action. What gives? Went bact to shoot my woof ammo, same problem. He also had his SBR upper and asked if I could try the new combo... worked 100% his 12" upper, my lower and my ammo. Maybe more pressure on the short bbl, if so why did I get the 6-30 rnd mags to run???
I did get to empty my Beta mag with steel ammo and his short bbl My Sendra under my Colt 
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Place to start would be to just examine the gas path in detail for any obstructions or leaks.
What comes to mind to inspect... Gas block loose, or show evidence of leakage? Gas tube look ok, no damage or evidence of leakage where the tube exits the gas block? Gas tube retaining pin still in place, no sign of the tube being loose? Inspect end of gas tube in the upper receiver for excess wear or damage. Inspect gas key and BCG for leakage or damage. Make sure gas key is not loose. Inspect bolt and gas rings for damage. If all that looks good, depending on the barrel/upper configuration I might give thought to pulling the gas block off the barrel and removing the gas tube from the block, to inspect for something like a fragment of a bullet jacket, or lead buildup from a .22 conversion, something like that that might be obstructing the gas port in the barrel or in the gas tube (as unlikely as that might seem). |
| I used to run into this now and again with steel cases ammo, since steel cases don't expand the same as brass you can have carbon buildup on the walls of the chamber which for whatever reason seems to stick really well to steel cases. inspect your chamber closely for carbon buildup. For me this problem arises usually when both brass and steel cased ammo is used in the same outing or if I didn't clean the chamber good enough. Another thing to consider is that the chamber is a little sticky (from the carbon) and you have a worn in extractor spring, after installing extra power extractor springs in my bolts this problem completely disappeared. I shoot a lot of steel cased ammo in different calibers and the extra power extractor springs in conjunction with clean chambers has worked for me. |
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Quoted:
Place to start would be to just examine the gas path in detail for any obstructions or leaks. What comes to mind to inspect... Gas block loose, or show evidence of leakage? Gas tube look ok, no damage or evidence of leakage where the tube exits the gas block? Gas tube retaining pin still in place, so sign of the tube being loose? Inspect end of gas tube in the upper receiver for excess wear or damage. Inspect gas key and BCG for leakage or damage. Make sure gas key is not loose. Inspect bolt and gas rings for damage. If all that looks good, depending on the barrel/upper configuration I might give thought to pulling the gas block off the barrel and removing the gas tube from the block, to inspect for something like a fragment of a bullet jacket, or lead buildup from a .22 conversion, something like that that might be obstructing the gas port in the barrel or in the gas tube (as unlikely as that might seem). If he needs to tap out the spent casing with a cleaning rod none of the above is the issue, carbon in the chamber is the culprit here, one way to tell for sure if after you used the brass ammo inspect it, the brass will take a lot of that carbon in the chamber with it because it expands completely into the chamber walls, so the spent brass will have carbon from the chamber stuck to it. |
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If he needs to tap out the spent casing with a cleaning rod none of the above is the issue, carbon in the chamber is the culprit here Carbon in the chamber is certainly a possibility with steel case and especially when mixing steel and brass, but his description of a sudden change to a short stroking condition led me to suspect a potential gas system problem. Gotta start somewhere and that just seemed the most likely culprit. Anyone shooting steel case should be aware of the gas blow-by issue and cleaning their chambers anyway. Other possibilities too like a lower-powered lot of ammo or the like. |
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worked 100% his 12" upper, my lower and my ammo. Maybe more pressure on the short bbl, if so why did I get the 6-30 rnd mags to run???
find out what kind of extractor setup he is using, I'm betting its either upgraded or the spring is in newer condition than yours is. Also if he was only running brass ammo through before it wouldn't have carbon buildup in the chamber, if you use brass you don't have to go crazy on the chamber cleaning but steel requires it. I use a section of cleaning rod with chamber brush in my drill and just go to town on it for a minute or so, not sure if this is advisable or not but this is how I do it and my chamber is squeaky clean in a couple of minutes. |
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Quoted:
Quoted:
If he needs to tap out the spent casing with a cleaning rod none of the above is the issue, carbon in the chamber is the culprit here Carbon in the chamber is certainly a possibility with steel case and especially when mixing steel and brass, but his description of a sudden change to a short stroking condition led me to suspect a potential gas system problem. Gotta start somewhere and that just seemed the most likely culprit. Anyone shooting steel case should be aware of the gas blow-by issue and cleaning their chambers anyway. Other possibilities too like a lower-powered lot of ammo or the like. you definitely raise valid points with the list you posted on things to check, its a good list and I didn't mean to sound like I was trying to discredit it or anything but I'm leaning to a fouled chamber because he couldnt repeat the issue with brass cases ammo. if its JUST steel cases doing this then I would say that the issue is pretty clear. But just ask my wife as she likes to point out I have been wrong a couple of times in the past 
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on clean up.
| if nothing else just clean the chamber, a good way to avoid the problem is to not shoot any brass in the same outing as the brass expands and crushes carbon deposits in the chamber making them harder to remove. if I'm shooting both in one outing I'd shoot the brass first then the steel. |
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