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FX Impact .25 with JSB MkII 33.95gr -- what FPS are you getting?

With 15cc Plenum tube screwed on where the reg gauge connect, I'm getting 910-915fps with 34g @140b as stated on the Waka gauge and verify by 2 other Waka gauge.

with external tube have 2 advantage beside getting more FPS without adjusting anything, at an average of 35-50fps more.

1. the refresh rate to 140b is so much quicker after the shot.
2. I can shoot to 10-15b below reg setting before the speed start to drop. 

the final tube will be 1 1/2" OD 3" long in black milled from a solid T7 aluminum tested to 300B 

 
Ernest I'm not sure how this plenum tube operates but it is interesting that you are getting such a large increase in velocity. Is it just a larger reservoir of air we are talking about?
Mine gets 860 fps maxed with 34gn Heavies. Other guys are getting much higher. like 880-895 I'm thinking that my probe is not lined up properly with the air transfer port.
 
"Drumsnguns"Ernest I'm not sure how this plenum tube operates but it is interesting that you are getting such a large increase in velocity. Is it just a larger reservoir of air we are talking about?
Mine gets 860 fps maxed with 34gn Heavies. Other guys are getting much higher. like 880-895 I'm thinking that my probe is not lined up properly with the air transfer port.


impact has a small air reservoir/plenum space so it's limited to around 860- 875fps.

when you shoot at reg setting at around 150b its doesnt have enough are volume to maintain a high bar setting through out the barrel length before the valve close and the reg takes a little longer to refill the chamber back to150b.

I bored out the TP to 4.5mm from external tube to reg chamber to have more air passage/less restriction.

The guy that has a larger lung will shoot a dart with greater velocity. !!!!



 
like I said with all adjustment max out with out adding any mods without going over 150b At an average of 5 impact tested got around 865fpd with 34g, some barrels are a little looser so you will see faster speed up to 880fps. 

With the mod external tube I'm thinking around 925fps with 34g at 150-155b reg pressure.

its more efficient at 140b with the added tube I have the option to shoot over 900fps.

 
Hi Ernest. That's impressive! Would it be impossible to make it square in shape with the bottom of the beach block and add the gauge back into that piece? 
I have no idea how you could machine that but you 
could potentially have a market for this in the 100's
Thanks for all your efforts developing these ideas. 
I'm another who has learnt a great deal from you. 
Michael
 
Agreed. Could also be a little less prone to knocks and maybe putting pressure on treads into the block. Also you could then still add a gauge facing forward. Could come back past the magazine if need be. Maybe you could put a small retaining clip around it that anchors into that bridge between the breach block and the butt pad. Something to stop it turning. 
 
Ernest in your effort to increase FPS by increase regulator volume, the question arises do you feel the impact (ST barrel) is more accurate at higher FPS 880 and higher than at 830 at longer distances (75 yards or greater?. At the end of the day more accurate is alway better than more powerful when shooting airguns right?
 
I am struggling to get reasonable velocities with the 34 mk1's. 
Eventually after watching one of are Ernest's video's I decided to have a look under the valve adjuster. Took it off and the stopper on the end had lost it's 1mm retaining screw and come undone about 10mm. 
(Just as Ernest had suggested they will)
I lock tight the tread and screwed it back in. 
I couldn't wait to get back over the chrony and sure
enough my velocity had come up to around 850fps from low 700's 
Then after a couple of magazines I went to adjust
the power wheel to find it had quite a bit of spring 
tension on it. 
I readjusted the screw on the power wheel and after that my velocity dropped right back. 
Anyway that made me think I have enough air pressure volume to push these pellets at 850fps so maybe my problem is either my 
hammer spring or possibly the valve spring not letting the hammer spring do its job. 
I've ordered a new hammer spring. But wonder about that valve spring. It takes quite a bit of pressure to pull that rod forward and do up the stopper on the end which I suppose the hammer spring must overcome. That's where I'm at now
This is probably pcp basics for many but all new to 
me. Any insights much appreciated. 
Michael