[lurkingknight]

somewhere between .28 and .32s anything in that range is good, heavier is better imo as long as you can afford it.

The PDI barrel doesn't have a square cut window, if you use that barrel it's better to have it milled square. That's the reason everyone uses prometheus EG barrels, square cut, very straight bore.

The kit and the tool are great, but unless you plan on doing many barrels, I'd just pay someone to have it done, Spike can do it for you, he's out in your end of the country. IF you have the hop up unit in your vr16 that is black and has 1 single dial on it, there's no real reason to change it.. it's a good unit, it's better than the ones with the 3 gears on it like the lonex.

You might want a flathop nub or mnub as well. You can use the standard round nub but you'll get better results with a flat nub. Or if you want to do permanent modding to your hop up unit's nub arm, you can install the mnub.

Have you fixed and upgraded the air seal on the gun yet? it is more worth the money to upgrade compression components before doing r-hop. The target for best performance is a spread of less than 10 fps in a string of shots. If your compression is leaky, r-hop will be as good as a standard setup.

Contact spike though, he can hook you up properly.