The NPAS system of nozzles for GBB rifles is an interesting design. Normally the nozzles that come stock in GBBRs are of a positive system meaning that the valve inside the nozzle is kept in an open state during the initial firing of the BB until the pressure in the barrel drops enough that the gas pressure overcomes the gas/spring pressure that is keeping it open. Once the valve moves forward and closes the system will begin to push the bolt carrier to the rear and begin the cycle. What the NPAS does is allow the distance and spring pressure that the valve has to move to be adjusted. When adjusted fully open the valve is further from the closed position and will allow more pressure to flow into the barrel and thus give a higher BB speed before the valve closes off. The reverse is true when the NPAS has been adjusted to an almost fully closed state. Less gas is directed into the barrel and before it begins the carrier cycle.

 

 

This nozzle is very clean and smooth. The molding seems to be of high quality and the machined components are good quality. The plastic seemed very sturdy and had very little in the way of molding marks or defects. The set came with the nozzle, keeper, c-clip, adjustment tool, and read o-ring for use in the WA replicas. As I was using an AGM I would not need this o-ring or be able to test it.

 

 

Testing was conducted at 70 degrees F. The NPAS was installed into two separate bolts. The first is a brand new AGM carrier that has less than 1,400 shots on it. The coating is still brand new in the cylinder area of the carrier. The second is an AGM carrier that has been turned .0001" over the original diameter of the cylinder then polished out with 1000 grit sandpaper and final polished to a mirror shine. This treatment generally increases consistency and overall smoothness to the firing cycle. It also replicates a bolt with much more wear on it. Testing was started with the looser bolt carrier in order to minimize the wear caused by the tighter carrier on the o-ring.

 

 I used .25g Stealth BB's (mainly because I have a ton of them and they are super slick). Since this test was less about FPS and more about adjustability they would work fine. All FPS can be adjusted for weight by calculating the FPS using the TeamDUCK FPS calculator. Shot strings were 9 rounds with 10 seconds between shots. The magazine was reloaded and topped off with gas in between strings and allowed to return to ambient temperature for 5 minutes. Before the 1st recorded shot was fired, the bolt was fired through 2 strings of 25 shots in order to check for any inconsistencies and to make sure that the magazine was at operating temperature.

 

 

The first shots were fired over the chronograph to get a baseline FPS spread so that I could get an idea if something failed. The numbers were consistent originally to around 20-30fps at the maximum. After around 40 shots were fired I noticed that the FPS dropped 150 FPS and the spread went to around 100-150fps. Upon removing the bolt I noticed that the adjustment flute valve was out of place similar to the 5KU issue noted in the first NPAS review article. I reset the valve in place and saw that the tip of the valve was missing. The NPAS was new and the valve was only turned one time to find the extremes while noting the number of turns. It had not been fired before so there was no way that this was a previously standing issue. Without the tip in place the valve would constantly come out of place. Also it defeats the purpose of having an adjustable bolt without a means to adjust it.

After doing a quick comparison of the flutes in the RA-Tech to the flute from the 5KU it appeared that both pieces were nearly identical and that the 5KU flute could easily stand in for the RA-Tech version for the duration of the testing. Another 50 shots were fired to make sure that the FPS did not appreciably change (it did not) and testing was finally resumed.

 

 

During the shot strings I noted a great many jams. The setup was identical (replica, mount, magazine, bb's)  to the 5KU NPAS in which no jams were noted at all so it was not a setup issue as far as I could tell. It appeared that the rounds were apt to double feed and cause damage to the nozzle tip. 17 jams total were counted during recorded testing. Jams during break in were not recorded so the number may be much higher.

 

 

After swapping to the newer bolt carrier (tighter tolerance) the shots strings continued with a slightly larger amount of jams per string. During the 4th string there were 6 jams out of 9 shots. Not a very stellar record for a new part. During the last string the rounds jammed only once. Upon closer inspection it was noted that the round had not in fact jammed, but the nozzle had completely broken. The carrier was stuck fully to the rear and held in place by the broken pieces of the nozzle. With small pliers I was able to get the small parts out sufficiently to get the upper receiver off to inspect the damage. What appeared to have happened is the keeper tore the back of the nozzle off during the cycle. The other interesting part was that the flute valve was NOWHERE to be found. The only parts recovered are shown in the photo to the right.

 

 

At this point in the testing the RA-Tech had majorly failed two times and had an approximate jam to shot ratio of 1/10 (17 jams in 171 shots). Even with the fact that the system is much more flexible FPS wise (60-450 FPS range) than the 5KU (250-460 FPS range) it was hard to put any stock in the system due to the failure rate and difficulties encountered. Having already worked with the 5KU system I was hoping that the RA-Tech system would impress me with the high quality of parts and durability. Unfortunately it was a complete failure and this after never having been used on the field or subjected to any dirt or sand.