[Future Snake Eater]

“Yet, out of a batch of 24 rifles, nine of them jammed at some point.”

This could also be a batch of crappy magazines. Usually that turns out to be the problem with my unit's M-16s and M-4s.

[winodog]

Does the ammo sometimes play a large part in malfuctions as well?

[Monty22]

I'd bet on bad magazines too. I have 2 AR-15s, one a CAR-15 shorty. They 100% picky on magazines. Either they work for 1000's of rounds without fail, or they will jam every 5-10 shots with particular mags.