Greetings.
The reason you cant have a full auto capable paintball gun, is, as my frinds have highlighted (yo guys) because: Paintball guns in the UK are classed as airguns. any airgun that produces more than 12 foot pounds of muzzle energy (about 360 feet per second velocity with a ball) is then a section 1 firearm (requires a licence). Then, any firearm capable of loosing more than one round per pull of the trigger, is a section 5 Firearm (not for public ownership).
Your way around this is to purchase another board which you can leave in the states and then swap them when you get there.
If you had the board in this country, it would be tantamount to having, said illegal firearm.
the average "PIG" as you so eloquently put it, may not be able to tell the difference and may not be likely to raid your house. But, when you spunk full auto paint down the garden and your neighbour wonder what the f*ck is going on, they might turn up. Then,they can send your marker to the more than capable ballistics department who will then slap you with a court case.
Get another board, leave it in the states!
Cheers
gaz