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Posted: 4/15/2009 3:47:03 PM EDT
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Greetings,
I am having a problem that I have never seen before and I was hoping for some insight from someone that is smarter than I. I have an AR that was configured for DCM. Never had any problems. I recently installed a new M4 type upper onto the the old lower. I am using the same BCG in the M4 upper that was used in the DCM configuration. When I went shooting yesterday I had a problem that occurred frequently. After a shot the shell casing always ejected fine. But at times the bolt would come forward only about half way. It would strip a round from the mag and the bullet would be half into the chamber, but loose, not stuck. I would have to remove the mag, pull the charging handle back to pull the bolt back enough to let the shell come out. I could not use the forward assist to move the bolt forward. But pulling the bolt back and letting it go forward would chamber a round fine. It seemed to be either short stroking or that the bolt was binding on something, but I can't tell what. Since I installed the M4 type upper onto a lower with an A2 syle buttstock, I wondered if the normal A2 style buffer tube spring assy is not right for the shorter gas tube on the M4 upper? Or does it matter at all? I wondered if you have to use a new M4 buffer tube / spring assembly to coordinate with the new M4 upper ? Any ideas from anyone on what could be wrong? Config: M4 upper Lower in A2 config The BCG and all lower parts are from the working AR 15 config with just a new M4 upper added on. I was using Prvi Partizan 55 gr at the time (first time for this ammo also) and had no other ammo to try. Thanks in advance for any help. |
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Bolt binding on the mag ?
Carrier key binding on the gas tube ? Incorrect barrel extension/receiver combo (i.e. rifle extension/M4 receiver) snagging the bullet ? Cam pin rubbing on receiver ? Will the bolt lock open when fired on an empty mag ? Could even just need to break in... how many rounds through this upper ? The buffer configuration should not be a problem. |
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Quoted:
Bolt binding on the mag ? Carrier key binding on the gas tube ? Incorrect barrel extension/receiver combo (i.e. rifle extension/M4 receiver) snagging the bullet ? Cam pin rubbing on receiver ? Will the bolt lock open when fired on an empty mag ? Could even just need to break in... how many rounds through this upper ? The buffer configuration should not be a problem. This pretty much covers the possibilities. |
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Bolt binding on the mag ? No, When the problem occurs I can remove the mag and the bolt stays in place. I tried multiple mags
Carrier key binding on the gas tube ? I don't know. I 'll check, but I would think if it was something like this is would bind everytime instead of intermittently? Incorrect barrel extension/receiver combo (i.e. rifle extension/M4 receiver) snagging the bullet ? You're obviously smarter than I, since I have no idea what this means. Cam pin rubbing on receiver ? Hmm, I didn't see any wear mark on the receiver but I'll look closer Will the bolt lock open when fired on an empty mag ? Yes, everytime. Could even just need to break in... how many rounds through this upper? Possibly, I have about 140 rds through it yesterday. Even though I had cleaned and lubed the gun before shooting, I noticed when I broke it down today that it seemed mighty dry. I gave it a thourogh cleaning and more lube than I would usually use and will reshoot this beast and see what happens. Thanks for the suggestions Brad |
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Quoted:
Carrier key binding on the gas tube ? I don't know. I 'll check, but I would think if it was something like this is would bind everytime instead of intermittently? Maybe, maybe not. Often the gas tube will move to accomodate the misalignment, so the problem could be intermittent. Quoted:
Incorrect barrel extension/receiver combo (i.e. rifle extension/M4 receiver) snagging the bullet ? You're obviously smarter than I, since I have no idea what this means. Make sure your barrel/receiver don't look like the "bad" example below (unlikely, but easy to check): 
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