I have no idea whether the Marine Corp uses the M-4 carbine with any regularity or not, but the M-16 jamming easily isnot uncommonby my experience in the Army in Kuwait, Saudi and Iraq, even with a weapon cleaned one or more times a day.
I knew the piece about the 45 was suspect, as I had a Remington Rand .45 as my sidearm in Desert Storm and it was a piece of crapolie with the barrel shot out.
M-14's were being brought over to theater when I deployed with 101st in 2003, and it has alwayshad a very good rep. The .50 cal Barret is a very good rifle for taking out personal and light-skined vehicles but obviously is not going to knock out a vehicle with one shot unless you got the engine block.
Interestingcorrections by "whoever" corrected the original email.