Originally Posted by
LimeSpoon
Quick question, have you checked extractor spring tension?
I admittedly don't know myself exactly how this sort of malfunction would happen. But if I were to try to play detective, I'd say:
1. The rifle previously ran fine with no issues, so this is probably because of some change to the status quo.
2. It appears this malfunction has only happened when it's cold.
3. Numerous high quality magazines have been tried so clearly that is not the problem.
4. Two different, quality buffer springs and 3 different buffer weights have been tried so that is likely not the problem.
5. The buffer tube is high quality and has not given you issues before. Possible, yes, probable, I don't really think so, or at least it wouldn't be the primary contributor.
This suggests to me that the malfunction might be the result of wear, temperature-induced sluggishness, or both.
Now, if I were to try to think of a plausible series of events...
Enhanced bolts sometimes seem to have weak extractor springs from the factory, for whatever reason. If this were the case then they might have largely worn out after 3000 rounds.
In normal temperatures this might not have been evident, but perhaps the cold environment is causing an increase in the amount of extraction force required. A weak extractor grip might hang on to the spent casing only loosely, resulting in a delayed ejection. (For that matter, you could also check the ejector spring.)
If the ejector doesn't manage to kick the spent casing out in time, then the bolt might stumble on the rim of the new cartridge (or possibly even ride over it completely and hit the base of the body) and push the rear end of the cartridge down, and in doing so cause the nose of the bullet to angle up. The same could happen to the next round in line. The bolt speed is reduced because of the cold and the clumsy feeding, which gives the magazine spring additional time to push up on the next round in the magazine as the bolt is closing. Having been tipped nose up, the bottom round blocks the bolt from going into battery, and the top round slides partway into the chamber through inertia.
If I were to suggest possible courses of action:
1. Check extractor springs & check under extractor to make sure nothing is impairing function there.
2. Check ejector spring tension. If possible, remove ejector and confirm that there's nothing in the channel that's binding it up.
3. Give the chamber a quick clean. A dirty chamber, especially one with any hard bits inside, will increase the extraction force needed. This shouldn't be the sole cause of the malfunction but it might exacerbate any other problems. Chamber mops are nice for a quick clean, even if they wear out quickly.
4. You can also give the buffer tube a quick scrub just for insurance's sake. The chamber mop might be handy here again.
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