The Hidden Shot.
Are you tired of mods that don't leave you to but your own spin on them? Well, this will give you a little room for originality.
Materials needed:
- Hidden shot
- 17/32" or 9/16" brass
- crayola marker
- PETG
- 2.5-3" CPVC
- electrical tape
- saw/dremel
- needlenose pliers
- sander
Well, this mod is very simple, and that's all you need to know.
Here is the gun before you do anything.

Image used with permission from wldworld, who happened to sell me that exact HS.
Pre-barrel Prep
Cut your stock barrel down to 2". Don't worry about cutting the pole, you'll get that out anyway.

Now take your pliers and rip out the pole in the barrel. You want to rip out very close to all of it, but you want to see a little bit of orange left when you are done.
Here is a reference:

Brass barreled
This is what I use.
Cut 3" of brass in a size of your choice. Use the pliers to flare out both ends of the barrel, to prevent dart slicing. Wrap in elctrical tape until it is snug in the stock barrel. Just for shits and giggles, I wrapped the end in e-tape and mashed the end of the stock barrel on there. I think it looks good, and by god you better agree with me.
Finished pic:

Marker barreled
This isn't the greatest barrel material, but if you want to use a crayola or Rose-art marker, you can.
Cut your marker like so and hollow out the insides. Wrap it a few times (2 or 3) in e-tape and wiggle it into your stock barrel.

CPVC barreled
This is a little harder than the rest, but it's worth it.
Cut about 3" of 1/2" CPVC. Use your sander to sand down 1" of the end of the CPVC until it is snug in the stock barrel. This will be the end that you will stick in the stock barrel. BE CAREFUL! If you don't sand off enough, you will crack the stock barrel if you try to cram it in there.
Here is a pic for you to go by:

PETG barreled
No, I don't have any PETG, but you would follow the same procedure as the marker barrel. I would use 3.5" of PETG, but you may want it a little longer or shorter than that.
Congrats, you're done.
Here is a pic of my hidden shot with all 3 (hopefully 4 someday) of the barrels.

And just because somebody may be wondering how it "folds up", here is a pic if the HS with a brass barrel, in its "folded up" form.

Ranges:
CPVC: 30ft.
brass: 35ft.
Crayola: 20ish ft.
Closing thoughts:
It's a pocket weapon. Get over it. It's not meant to be "teh uber 120ft NF smg". It's meant to be a last resort. It's small (slightly larger than a SSPB, when folded), but not incredibly accurate. That's because the barrel rotates. It's a little hard to aim, but once you get used to it, it's not that bad.