The gun will not hold air

https://www.ereplacementparts.com/porter-cable-fr350a-round-head-framing-nailer-parts-c-129_1719_2241.html

http://www.ereplacementparts.com/porter-cable-fr350a-round-head-framing-nailer-parts-c-129_1719_2241.html

Air leaking out of head and driver extended indicates that the cylinder seal is bad and or the head valve is sticking or stuck in the head. Easy to check by removing the head and looking at the large plastic seal on top of the cylinder. If seal looks good, pull out the head valve and lube with white grease. Parts are here :

Good luck

Are you depressing the nose of the nail gun against the material to be nailed first? Without doing this, the trigger will not "unlock". You can read a pretty in-depth review of this nail gun at OnlineToolReviews com Porter Cable FR350A Full Round Head Framing... which might also help.

Most likely orings will not blow out when over pressure. More likely the cylinder seal has cracked (vinyl seal sitting on top of the cylinder). Also check the upper bumper for cracks and replace as needed. Lube orings with plenty of silicone paste lube and retest. Good luck

getting that screw out isn't going to help. You have a broken seal or o ring in the cylinder area. You need to remove the 4 bolts that hold the cap in place. You might want to take pics of the disassembly or you can also go to "dewaltservicenet.com" for a breakdown.

By looking at the picture it seems you have a framing nail gun, you can't load staples in it!!

No... it will fire 21-degree nails and perhaps 23-degree nails (but sont think they exist) and it is a full-head framing nailer so it is designed for firing round head nails. Using clipped nails will likely jam the nailer as these nails are stripped closer together with overlapping heads in the nail strip and the FR350A has a full round driver so you will run into issues with clipped nails. If you are having problems finding full round head nails, you can find them on Amazon to fit this nailer. Otherwise any good tool or trade tool store that sells nailers will likely have a suitable nail supply available for the FR350A.

Here is a link to the manual for your nail gun. Refer to page 11 of the manual for removing a jammed nail. To get the manual, go to the link, click on the "Manual" tab and the in the gray box, click on the name "FR350A Manual". The link is:

http://www.tylertool.com/porfrrounhea.html

Hope this helps. If it does, please leave feedback.

check for a jammed nail in the magazine/nose area. also I would check to see if the driver is bent and not allowing it to move freely. Check the warranty and see if you can take it back and get it repaired or replaced also. Let me know if I can help further