All paintball guns, excluding high end guns, have a .685 bored barrel.
Any autococker threaded barrel.
It depends on your budget. For under 100, the Azodin Kaos or a used Automag are solid choices.
I would guess that you would have to buy it off of a website like kijiji or Ebay
Firstly, the Blitz is built on the koas model, plus an adjustable blade trigger, ramping (near fully automatic) board, eyes, regulator, macroline system and is the "middle grade" in the Azodin line. The kaos and GTI are entry level markers, and the Blitz was designed as a mid level gun, so there is really no fair comparison. In addition Piranha gti is a relatively old, and in general low quality gun compared to the entire Azodin line.
Tippmann 98's, spyder mr1/victor, and azodin ats/kaos are good to start.
Yes, the "D" if for "deluxe" meaning a better marker than the standard kaos. Since the kaos-d just came out, it will be a few months before anyone can make an educated statement on the differences. Personally for the price of the D, you could buy a Blitz which is electric (ramping/full auto) higher end version of the kaos.
The spyder victor is a more reliable gun than the JT. You should also look into the Azodin Kaos.
Definatley the Azodin Kaos. Its as simple as a spyder with quality parts put in. Out of these It has the best trigger and threadings (all standard) which make it easily upgradeable. It also won the Techpb award in 2009 for best sub 100 dollar gun.
dude a planet eclipse for an electronic gun if can spend alot, and an ion if u r on a cheap budget. for semi markers i would recommend an azodin kaos for a cheap budget and a tippmann brand for woodsball.
No, they're only good for backyard shooting or experimenting. Get a Tippmann or Spyder if you're starting out. I would recommend an Azodin Kaos (based on your price range). It's 90 dollars and it's semi auto
They are both so close in performance it could just be a matter of which one feels better in your hand. The only thing the G4 has over the mini is a better asa, but that is a fairly minor detail.