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Posted: 4/5/2005 10:29:35 PM EDT
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I have recently aquired an upper. Ok here is my dilema. The only ammo I have is 5.56. I load it up and charge it and the bolt sticks on the 1st round in the mag making a huge scratch in the bullet casing. If I pull back the charging handle just a bit and release it....it will chamber the round and will completely fire just fine untill the mag is empty. It does this every time. Ok, I start thinking about it. The barrel is marked "BM 5.56 HBAR" hmmm, this has to be a Bushmaster barrel chambered in 5.56. Ok, no problem there. Don't have to be a brain surgeon to figure that out. Now I know, usually, if you buy a barrel seperately the barrel extension is not included. If you buy a complete upper..... I THINK the extension is in there. Hmmm. So now I suspect I have a frankenupper. Is it possible that I have an upper intended for .223 mated to a 5.56 barrel ? Or am I barking up the wrong tree ? This is what I am thinking..... I think my upper is for the .223 and when I try and chamber a 5.56 its causing it to hang up and the reason the rounds fire correctly is because the barrel was made for that round. I don't have any .223's to try so I will have to get some. I suspect they will chamber fine. The upper receiver has a "keyhole" rollmark beside the rear sight. What company produces these. I suspect this is Olyarms and if I recall correctly, they are chambered for .223. Am I right ? Thanks for any help. 
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uppers aren't caliber specific. are you riding the charging handle on the first round? barrels come WITH the barrel extension installed in all but extreme cases. the extension forms part of the headspace. the keyhole mark is Cerro Forge, it's anyone's guess who did the machining. BFI used Cerro Forge blanks. |
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Ok, so what you are saying is that the upper receiver may be Bushmaster as well ? Cool. I don't think I am riding the charging handle. I pull it back and then hit the bolt release and thats when it gets stuck. Like I said earlier, I then just pull it back and release it again and it chambers. I put the bolt in my Armalite and nothing happens so I know its not the bolt or carrier doing this. Its not the lower either as I put this upper on my Armalite lower and it catches on that one too. Something might be wrong with the receiver ? its not my mags as it does it with all of them. I'm just trying to go by the steps, one by one till I find what the problem is. 
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Download your mag by 2 rounds (18 in a 20 or 28 in a 30) and try again. Sometimes with a brand new mag, the mag's spring tension is so high that the bolt has trouble stripping the top round off of the mag. By underloading the mag by a few rounds, this should go away. If that's the problem, then you're fine, because with a little bit of use, the mag springs will loosen up on their own. -Troy |
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I tried the mag thing and it still did the same stuff. I knew it wasnt the mags anyway cos they work fine in my other AR. Upon closer inspection, I notice that the bolt is not catching on the bolt catch, it catches on the back of the cartridge. This only happens with this specific upper. I can get it to work right if I lock the bolt back before I insert the magazine and then release it. Sometimes it doesnt even hold open after last round has been discharged. Strange. Is there any way to fix this problem ? |
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Does the upper have M4 cuts and the barrel extension ramps not lining up? I ask this because a while ago I acquired a barrel and upper with this same problem. It took a little dremel job on the barrel extension ramps it everything fit perfect. This could be holding the first round long enough for the bolt to start gouging the shell case. Once you start cycling it the spring pressure from the magazine lightens and the rounds feed fine. This is just an idea for what could be happening. |
That's a shortstroke, there are a dozen threads in Troubleshooting right now dealing with it. That doesn't explain why it won't load the first (hand cycled) round, but based on what I can decipher of your post it sounds like you're riding the charging handle. I think you need to read the -10. |
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