That looks like more than a squint.
There are flash guns which don't use shells but ignite gas for the flash and prop guns like Once Upon A Time In Mexico that are completely non-functional where they add everything later digitally. Also some times they lighten the powder load in the shells for the blanks. But from everything I've read about T2, they were just your standard blanks being utilized by real firearms (except in the case of stunts where they were rubber). The irony here is, with the spring tube being the way it is, there's very little kick to an Armalite compared to other assault rifles so why she's squinting is anyone's guess, and I'm guessing novice.