Northern Tool vs. Harbor Freight vs. name brand....
I "made do" with a HF framing nailer for several years, and it had a really bad habit of double firing. It was the older model with the clipped nail design. Also, my air compressor would go down to 80psi before it kicked in, and the HF nailer would leave the nails sticking out slightly, so I'd have to go back and nail them the rest of the way in.
The last straw was the double firing. I was up on a ladder putting up a 16' long 2x6 (fascia board). Did the double nailing thing, but the second nail just went into the very edge of the board and then straight on through. My hand was 6" behind, well out of the way, so I thought. Broke through my glove, into the skin a little way. Not bad enough to require a doctor visit, but I did quit work for the day. Bought a new Porter Cable the same day. It has a single fire mode that I always use. Bonus is that nails are easier to find for it, and they always go in all of the way. I caught a sale and got the PC for $179. You can pick it up for $189 from Amazon.
Amazon.com: Porter-Cable FR350A Round Head 2-Inch to 3-1/2-Inch Framing Nailer: Home Improvement
After using the PC nailer for a while, I realized that the spring on the foot of the HF nailer had too much "spring" to it, meaning that you had to really push down on the HF nailer before you could pull the trigger. I took the spring out and cut it down a little so that it was closer to the amount of pressure required of the PC nailer. After I made this modification to the HF nailer, I no longer had problems with double nailing.
However, the PC nailer was just all around a better gun: depth adjustment, single fire mode, set the nails all the way, easier to find nails, and you could find truly galvanized nails for it. (HF has nails they call galvanized, but they aren't).
Now I keep the HF nailer around for people who want to borrow my framing nailer....
After using the Porter Cable