Looks stock (all right, with a mouse-pad-bedded barrel), right? (The zip-tie loop off the scope is for me to hang it off my arms rack in my office.)
Nope. It's got a breech. It's made out of OMC PETG and some copper tubing someone left me. The seal is almost perfect - it can vacuum-load the dart if it's dropped in the muzzle. The barrel is copper over the PETG, under the CS-6 shooter barrel, and the copper + orange barrel extends about 4" past the end of the PETG.
And and, what's better, it takes CS-6 clips. The breech is just a 270-degree rectangle filed out of the the copper pipe, By hand. Yes, this is a one-off. The top of the breech is wide enough to keep the clip in place. You can only load the clip with the breech closed - the PETG spreads the lips wide enough to seat properly.
It tends to shave about 1 in 20 darts or so. No ranges - it's good enough for Office Wars. Oh, and a parting shot of it ready to rock:
If you look at the screw hole, you'll see the CS-6's 'clip notch' is a perfect height to the rear edge of the magazine well. I just lucked out.
Fugly is a feature.