ABS pipe, PVC is too heavy. ABS is lighter and it seems to be just as durable.
The core material is some 40# urethane modeling foam. I got a bunch from my model making class 2 years ago, but now i have very little left and unsure where to get more
I tried the 20# first, which I have much more off but it didn't hold up very well. Urethane foam is alot like wood, but there's no grain and it's unaffected by water. I'd say it's softer, easier to work with. It also doesn't burn or char like wood, its very easy to shape with high speed rotary tools like the Dremel.
I just finished the suppressor, the problem turned out that it wasn't attaching to the KMP9 properly, it's just a tiny bit crooked. I fixed that with a round file an some super glue. It's still not perfectly straight, but it's good enough. I added the piece to the front. it's not perfectly round, there were still a few issues but now it looks alot more complete. it works a little. not as well as I'd like, but at least it looks nice. Much to my surprise, it also increases FPS by 30!
I think I will need a lathe at the minimum to build a better replacement for this one. there's really no way to make parts with the precision of machines by hand. If there was just some way to make two perfectly concentric circles one within the other, then I'd be all set!
Currently all the parts are completely shaped by hand. it's really not hard to get the cuts to be the right dimensions, but to get the tubes perfectly concentric, it's nearly impossible.
I previously avoided this problem with a longer attachment method. Such as the Mark 12 suppressor. http://i.imgur.com/q2CgR.jpg
Half of the space in that Mark 12 suppressor is used to attach it to the gun barrel. less precision is required to make circles concentric, more precision is used to create the baffles within. actually there's only one baffle, and it's actually a ballistic stabilizer, not a baffle. it stabilizes the bullet leaving the muzzle, decreasing groups about 30% and theoretically increases range about 30%, but that would push maximum range beyond what is practical...
It's just a piece of foam shaped very precisely with one hole of the exact size in the center.
the muzzle hole of the Mark 12 was originally 0.228" (bullet's 0.218), it's made with the utmost precision.
The Mark 12 is so effective that I can shoot and you wouldn't hear it 50 feet away. 10 feet if we're in a noisy urban setting.
I I get a gas airsoft sniper (bolt) I might build a suppressor like the Mark 12 for it... for airsoft it's highly possible it can do away with the shot noise entirely.