Just to be clear, Is it failure to feed from the carrier into the chamber or is the carrier unable to travel up (I think that's what you meant by jamming out of the magazine, but wanted to make sure)?
Just to check this isn't defective ammo, what is the COL you measure?
The only other thing that occurs to me, if the COL is right, is the tips catching or dragging. Look at the one that wouldn't feed and see if you see marks left on the tip. You could color one with a dry erase marker and look for scraping. If it's a sliding issue, try rubbing the tips against some paraffin wax.
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