Only just got it, secondhand so not sure the person I got it from said he never changed it, all so having a problem with it firing, when I press the trigger it fires as in full auto and have to remove the air bottle to stop but if I change the bolt to one from my other SLG a 2010 model it fires ok so I think it's the bolt that is at fault there the only difference in the two bolts I can see is the UL one is plastic and the 2010 one is metal,