I hate to ask and completely reveal my ignorance. I've learned a lot about ARs since I've been here, but I know I still have a lot ot learn.
My understanding is that with a shorter barrel, the gas port needed to be opened for proper function.
My guess (from what I've learned) is that the carbine length systems have been plagued with too much gas, too fast and that has decreased dwell time an drocketed that BCG faster than it was intended by Papa Stoner.
Now, I'm getting on my thinking hat and grabbing the calculator and cold glass AR Kool-Aid. Therefore, if the LMT 10.5" upper is using a small gas port there will be less gas blasting away at the BCG, and there would be no need for a heavier buffer to decrease dwell time. Am I hitting anywhere close?
Also, I'm sure a properly maintained Mil-Spec will last beyond 5K rounds. BUt I like the CS because it lasts for a min. of 500K compressions. That means I'll (most likely) never need to replace it. I like that
. Plus it adds a little more resistance slowing the dwell time.