kjw G27 Metal slide won't fire after one shot.
 

I just picked this up froim a friend it has been a wallhanger for over a year. Cleaned and lubed it. When I gassed it up and fired the first shot fine but after that the gun fires gas seems to fully cycle but the bb just drops out the end...

I cleared it and reloaded and it does the same thing again.

Any suggestions?

You're hop up rubber may be damaged. Check to see if everything is in tact. Also check you're piston head/loading nozzle if they are still ok. Sounds like there is a loss of compression that prevents the gas from propelling the BB.