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Just to add some things about this nozzle.
I've been tinkering a bit with mine since I got mine from Garrison. In the beginning I was having a load of issues with velocity fluctuations. When I disassembled the nozzle from the bolt carrier, I realized that the tail of the NPAS was screwed so tightly on that when I attempted to increase/decrease velocity it would just unscrew the piston head instead of the NPAS. Referring to TPM001's pic on the third page it is the part with the larger o-ring located at the rear of the nozzle with the NPAS tail. I had to remedy this by locktiting the threads on the piston head to keep it in place while I adjusted the NPAS. Unfortunately the small grub screw didn't hold it in place as well as I thought it may, so this was my only solution.
If your nozzle does the same thing as what mine did, a tell-tale sign is that your bolt no longer fits properly in your receiver as it protrudes out the back of the upper receiver and catches on the buffer tube. This is caused by the piston head unscrewing and seating the entire nozzle further forward than usual. You can also check by pulling the nozzle until you can see that the piston head is seated properly in the nozzle body (ie. no gaps).
One last thing I had to do was sand/file done the edges on the lower half of the bolt carrier as it chewed an o-ring. Only took a bit of sanding to smooth out the lower edges so that wouldn't happen again. I only took fine grit sand paper and smoothed out the edges, I didn't sand any of the internal where the nozzle sits. This was on a stock bolt carrier.
Hope this helps somebody.
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