You can watch videos on Utub to learn and get ideas for making silencers.
I'm making my own ones, as I can construct them exactly as I want them (length, diameter & sound absorbing material). Is much more cheap and working.
x2 homemade silencers for my bolt action and DMR rifles: 17.5x4.5cm / 26x3.5cm
x1 Nov's for SSX23
Don't you have inner wall bbs impacts with such long silencer?
I haven't had issues with that except my 6.8mm end insert for maximum suppression, but my R-hop and nub weren't centered at the point I tried it, so I would always clip or catch BBs.
That was more than a year ago and I've learned a lotta and gotten much better at my stuff, so I think I'll try an ultra tight hole once I finish my 5.97 carbon barrel and VSR-SS.
Still, one .30 in your magazine and you're gonna need to remove the suppressor with holes that small, but you can usually get away with 8mm suppressor holes as long as your inner barrel is centered and your suppressor doesn't bend.
That's relying on you having good hole cutting skills tho.