If you can, or in the future, check out Online Metals for a metal tube maybe, they're pretty cheap in that size and will work better.
Carbon fiber is another option from eBay, about the same price but a little lighter.
Plastic and carbon fiber have poor sound dampening qualities, and the ABS pipe is likely heavier than a thinner wall metal pipe or a piece of carbon fiber, so it's likely not the best option.
One thing you should do with any suppressor or outer barrel on this is paint it with some sort of rubber paint, as my best suppressor had a rubber paint over a thin walled aluminum tube.
Otherwise, good work so far.