In an AR-15, they had a printed lower receiver stand up more than 600 rounds before it failed. Not good from a long-term standpoint, but more than good enough to work your way up to a metal version in a pinch.
The receiver in the Ruger Charger doesn't come under the same extremes of pressure that the one in the AR does, either. I'd bet you could easily get two bricks of .22lr through one before you experienced any issues.
Used properly you only need a few shots out of one. Then you can take the metal guns from the blue helmets.