Impact external plenum only 30 fps increase?

[Airmanator]

Anyone that has an external plenum. How many more fps do you get from with and without the external plenum? I average 930 fps without the external plenum with 34 gr jsb. I install the yong heng filter as the external plenum and I got max of 962. That's about 30 fps increase only. I was expecting like 80 fps to 100 fps increase. 

Note: I have enlarge both brass transfer port and probe, 6g hammer weight, 6.4mm valve seat, c3 o ring change to derlin and reg pressure at 160 bar for both testing.

 

[heavy-impact]

Did you drill the hole where the gauge used to mount to 6mm and cut the bottom leg off of the valve housing ?

 

[heavy-impact]

The yong heng housing is only 20cc. Most other custom ones are 30 to 70cc.

 

[Airmanator]

Did you drill the hole where the gauge used to mount to 6mm and cut the bottom leg off of the valve housing ?

Yes I do. I cut the leg blocking the reg hole. And drill the hole where the guage sit to with a 6mm drill bit. I'm just asking is 30fps expected from a external plenum? Cause that's not much imo. I was just expecting to get more power to shoot slugs.

 

[heavy-impact]

I have 95cc total plenum and get a little over 100 fps extra in .30 cal with 50 gn pellets from a 700mm barrel.

 

[Long_Gun_Dallas]

Sounds about right for that mod 

 

[mtnGhost]

Check your velocities at 130, 135, 140, 145, and so forth.

 

[PaniSd]

I think you go over pressure with it ...I have same as you and with 60cc external plenum on 100bar I have that speed with 34.95grain Jsb. 

Try to lower pressure and start again