– The Gas cartridge may be empty (check “Inserting the Gas Cartridge into DDF5110500 & DDF5120550 Gas Nailer” FAQ) – If there are any stuck/jammed nails please view the “ How do I remove stuck nails from my DDF5110500/DDF5120550 Gas Nailer? FAQ.” – Check if there are nails in the magazine / Magazine slider not retracted – Please see How do I insert nails into my DDF5110500/DDF5120550 Gas Nailer? FAQ – We only recommend DEWALT nails otherwise you may void your warranty. DEWALT Nails Length 15 to 40 mm Diameter 2.6 mm, 3.0 mm, 3.7 mm Nail Head 6.4 mm Type Of Nail Flat head, Round Head DEWALT Gas Cartridges Art.No. DDF5140500 – If the magazine is "bent" or not inserted properly/Magazine slider spring defective please see - How do I replace the magazine on my DDF5110500/DDF5120550? FAQ. – If there is a foreign object in the nose piece or magazine - please view the “ How do I remove stuck nails from my DDF5110500/DDF5120550 Gas Nailer FAQ.” – If the Gas Nailer is defective - Have the Gas Nailer repaired by an authorized service agent.