I have a senco sfn30 and it only shoots every second nail in. I had a look and the firing pin only retracts bout half way down???

There are 4 main causes usually with this tool:
1) Check the seal in the bottom of the cylinder (under the bumper) #BF0070 (#12 on the breakdown) If this seal is missing or worn the piston will not always return fully.
2) The pusher spring #GD0253 in the magazine is not moving the nails forward
2) The driver is bent or the tip is worn / chipped
3) The check valve ring #LB0077 on the cylinder is not sealing properly
Let me know if this helps Senco SFN30 15 Ga Finish Nailer Parts

Your driver is not returning fully.
Most often this is caused by:
1) A bent driver blade - pull the driver out and inspect it, make sure it is straight.
2) A broken seal o-ring on the bottom end of the cylinder (#66)

Senco SFN30 15 Ga Finish Nailer Parts

Senco SFN30 Parts List and Diagram eReplacementParts com

I have a senco 3C0001N the nail doesn't come out.

You have damaged o-rings in the gun. Remove the head cap & valve assembly, remove the ring on top of the cylinder, remove the cylinder & piston. The cylinder is in tight so work it out carefully. Check the condition of the following: a split flat ring with a rubber o-ring under it on the top of the piston and two o-rings on the outside of the cylinder. If these are damaged air will leak around the piston instead of pushing it back up. The inside of the gun should be clean with a light coat of oil on everything if you are oiling it properly before use. Dirt in the gun means the gun is being laid on the ground without the air hose attached. Dry innards means no or not enough oil is being put in the gun before use. Oil pooled in the bottom of the gun means too much oil is being used. Senco doesn't make a rebuild kit for this gun, you'll have to go to the Senco website http://www.senco.com/ or other website like http://www.ereplacementparts.com to get a parts breakdown of your gun and order the o-rings (any part beginning with LB) individually. If you replace one, replace all of them and grease them up liberally when reassembling the gun.

Not sure about Senco but most have latch you can open to expose firing mechanism. Nail sometimes gets jammed and will not allow driver to fire or if not nail push driver ****** all the way back into gun then see if gun will fire.

you need a top end rebuild kit

the 601 had a design flaw, in the nose, where the nails hit as the are being pushed forward, the peice was made out of a peice of metal that was too soft, it wore down and that is where you get the double nail problem.

Senco offered a trade in, this was years ago, for a limited time and gave us credit towards new guns, which we gladly did

i would double check the plunger to make sure its resetting after each fire.

firing pin called the driver is probably broken or needs new seals max air pressure 125 psi senco sells repair kits