Originally Posted by
interfan
Look at total cost of ownership, not just the individual weapon costs. If the USMC changes to a shorter barrel, then they have to get new racks, new vehicle mounts, new shipping containers, make more changes, obsolete a bunch of ancillary components that they would have to repurchase, etc.
For a small service branch, it is a costly proposition and disproportionately more expensive than say for the Army or Navy to make changes since they have a much smaller budget/man to begin with. If they were going to make all of the changes, they could just switch to a MK16/17 or IAR or something as the costs would be equally unaffordable.
Not to threadjack or move off-topic to a political rant, but the Marine Corps should have more money as it has been proven that they can do things much more efficiently and with much less waste than Big Army. If sequestration goes through, they're scheduled to be taking a huge hit; but the politics of that with the current admin is another topic entirely. /rant