Reply To: SPA PR900W review – a great super cheap PCP gun

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Pope_on_Dope
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Hey Dave, 

nive to meet you again, didn´t know you´re also on airgun nation 🙂 

Sure, here you are – please note that I made the drawing for another air transfer port as I wanted to see if I can get even more power out of it. The sub 12 fpe hole is of a 0.055″ (or 1,40 mm) diameter, not 1/7″ as in the drawing. The port shown on the photo is actually the sub 12 fpe version. It also has a champfering on both sides (see photo), I guess it will be sufficient to take a bit larger drill and just slightly widen the tops of the holes by a little bit. No need for polishing – air transfer ports hate mirror like surfaces. 

If you want it for an indoor range, you might want to try to make it as weak as possible. Germany, Italy and Hungary for example have a 5.5 fpe limit on airguns and they still sell them in .22 caliber so a 10 meter target rifle will still be perfectly accurate with ridiculously low speeds like 450 fps. You can try to make the hole even smaller like 1 mm or 0.040″, chrony it and work your way up from there to get your desired speed. Or possibly just make multiple ports, for example 0.040″, 0.050″ and 0.055″ and try out what suits best.

The 0.055″ will deliver right around 550 fps and due to its choking effect on the airflow kinda regulates the rifle so there is not much fluctuation. Its not like going between 700 – 850 fps like the classic unregulated high power rifle but more between about 530 – 560 fps, there will probably be no bigger total spread than about 30 fps and the rifle delivers between 10 – 11 fpe with a JSB Jumbo 15.89 gr. The effiency is catastrophic and will be just about the same as in high power as the rifle releases the same amount of air but you got yourself a cheap regulator. lol  

The British have been smoking rabbits out to 60 yards with sub 12 fpe rifles so they still pack a good punch even at range but the drop of a .22 is insane.  

Cheers, 
Falko