you're thinking of the burst fire m93r. You can get a uh mac10 or an mp7
http://www.airsoftgi.com/product_info.php?products_id=5635 but i kinda doubt you've got the money to drop and honsetly, i'd use that as a primary instead of a secondary
you need a propane adaptor, put adaptor on propane can and push then push adaptor into the hole on the bottom of the mag to fill it, pull bolt/slide back and shoot
Umarex is just a rebrander, they don't actually make guns, the gun I linked you to is a KWA Mp7 licensed by Umarex because, they've got a deal with H&K. that gun you linked to is a rebrand of the Well R4. green gas is propane with silicone oil added, don't waste your money, just buy thishttp://www.airsoftgi.com/product_info.php?products_id=4534
These places have really expensive AEGs try airrattle.com or airsoftmegastore.com
got my airsoft gun on friday, its a spring colt(6 inch model i belive?) has 3 rails and a pressure senstive laser sight, i havnt shot it yet, but will tomarrow <3
i had that gun before, from your description.it sucked serious ass.