The other material, acrylonitrile butadiene styrene (ABS), could produce a gun that fired 8 times without incident.
The agents stopped shooting after 8 bullets, an ATF spokesperson said.
These aren't intended to be highly engineered precision weapons. If you expect that, you're missing the point. However, a downloadable gun that will fire at least 8 rounds without failing... that's quite useful to some people.