Dunno what y'alls gun laws are like... but anything made outt'a metal is prob'ly a no-no. I've made 'em for .58 cal paintball guns pumpin 577 fps ... 'n they work.
The larger the internal area the better the silencing. I used a paper tube... but I s'pose you can use PVC. The end plates and baffles were wood. Two end plates (one threaded) 'n 3 internal baffles. These of course allowed the round to pass cleanly, but the pieces were drilled evenly around their circumference between the edge and the center bore. You can use as many baffles as you can... but allow for space... In that space... you'll use closed cell foam... similar to that thin yellow stuff found in padded ironing board covers. You can use two or more layers of that (loose)... leave an air gap between. If using a cardboard tube... coat the thing with some kind'a glue 'n wrap with cloth. I used a camo bandanna for that. You could also use colored cloth duct tape. Now... you'll need somethin' to adapt the gunbarrel to the silencer with... so I'd use a section of PVC (slotted to allow for the sight) 'n secured with 3-4 set screws. Thread the front end of this (make thread) to match the silencers internal female threads. Make sure they're straight. I put a small brass screw in the top of the silencer to aid in aiming... but that's up to you. The longer and fatter the silencer... the better, but you'll still need to 'aim', so it can't be above the front sight post unless you have a scope on it.