The Lancer AWM spring and the PMAG Gen III spring on the mags I gutted look literally interchangeable, right down to their "finish".
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-The action spring is within spec, and will strip a round and chamber it when released nearly touching the rim of the round.
-I cannot possibly believe that a 10.5" gun running a can and an H2 buffer which will also cycle without the can, could possibly be short-stroking.
I just did a quick experiment. The Lancer AWM's magazine follower required 3.70lbs of pressure to depress the follower .5". The PMAG gen3 I used to compare required 3.25lbs of pressure to compress the follower the same amount. If you subtract the weight of the PMAG gen3 (.32lbs on my digital scale) and the weight of the Lancer AWM (.27lbs), the difference grows slightly....I measured vertically so the weight of the magazine bodies must be accounted for.
Lancer= 3.43lbs of pressure to depress the follower .5". PMAG = 2.93lbs to depress follower .5".
Both magazines have exactly 30 rounds through them and were then put away for storage. The difference is not very big, but it could make a difference I suppose. The Gen3 PMAG has a stronger spring than the MOE/RevM.
EDIT: The springs may very well BE identical...but differences in body geometry and internal space could also be a factor...potentially adding some pre-load to the follower via the spring if the same spring is compressed to a higher static percentage.
I agree the difference is not that big and it might have zero effect on this issue. But the difference in pressure is still almost exactly one half-pound.
EDIT: Also possibly playing into the freak-incident......the matte finish on the metal feed lips of the AWM could add to the friction on the case as its being fed as opposed to the smooth face of the PMAG's polymer feed lips.
It varies by many many pounds over the course of shooting the entire mag, and malfunctions don't happen all in the first 25% of the mag, IMO/IME. I just don't think it's the issue, here. I think nose-diving is, caused by the lower being funky, and the mag being a bit more sensitive.
Possibly an out of spec case?
Keith
I have had issues on another rifle with this type lower (Gen 2 FFL) and Lancers that could result in this malfunction if the round BARELY made it into the chamber.
The case ejected and seated in the chamber fine once I cycled it again. I doubt it was out of sped.