had a look found the problem it was where the connector went into the rifle one of the pins had came a bit offset now it fires but every time it does the spring seats to the rear of the gearbox and lock backs there is a button to push to release the tension but I don't know why it locks to the rear
there is a way to push it down and tighten it but not sure if its wise and the mag still doesn't feed properly I know where to buy a new mag its the cloth one slightly smaller but its 94 quid seems a tad steep any more help would be appreciated cheers