But as long as it's been bumped, anyone know if they make HDPE in a high enough pressure rating? That would be great for LAWs because it doesn't fragment and shatter like PVC, it deforms and tears. It's what we use for aerial mortars so if a lift charge fails or a shell is loaded upside down there won't be shrapnel thrown like a grenade when the burst charge goes. It simply balloons out and literally tears a rip down the side of the pipe.
But again, I don't know if it comes in a high enough pressure rating. And in smaller diameters especially any lenght over a couple feet is fairly non-rigid making it bad for barrels. But for an expansion chamber it could be a safe way to go...
Yes this a bit old but....
The only problem with HDPE that I know of is the means by which you join it. I don't think that you can glue it as you would PVC. As far as I know it is typically joined with heat and or sonic methods.
Another option is SCH 80 PVC pipe and fittings to add some safety factor. Pretty much all hardware stores stock SCH 40 pipe, but 80 can be had in some.
As others have said and I agree, these are safe if constructed correctly.