FX hp plenum help please

[MrK]

Hi all,

Whilst impatiently awaiting the arrival of a wika manometer ( likely stuck in customs ) i have been wondering what method others who have upgraded to the hp plenum have used to seal a gauge on to it?

1/8 fitting. Recessed lip which seals with an o ring on blanking plug. The hole is “ bottomless” so no chance of o ring / x ring under thread.



1/8 Dowty ring. Seems to have lots of side to side movement in hole. Just seems there is nothing underneath to rovide a good seal the floor where the original oring on plug would sit being to deep.

 

[MrK]

Pic of blanking plug to give an idea of the relief machined into plenum

 

[Buglecall]

I used dowty but it never sealed correct.
I went with Oring over the gauges thread stem,works fine.

 

[MrK]

I was beginning to consider that may be an option but geat to hear it from somebody with first hand experience of doing-so. Thank you

 

[Buglecall]

I used the SHP first BUT found it too big for my taste.
So bought the SP, shot count went down a fair bit compared to the SHP.
To be honest i thought the SP was a bit bigger,don’t think i would of bought it,if i had known that.
Somewhere between the two would be ideal,great look AND worthwhile added shot count

 

[MrK]

Just received notification my parcel is now in the country so guess i will find out soon looking to experiment as i have read running a lower reg bar can help smooth the shot cycle and consistency any shot increase will be a bonus plus the benefit of having a dedicated bleed screw.

 

[Buglecall]

Make sure you note the REGS original BAR setting.
They vary wildly from factory. It will give you safe point if you don’t run the Plenum.
I found out that if set to low i was getting a high spike just coming of reg, over limit in fact.
It took me a lot air dumping and reg adjusting to get what i think is ok.
Its not been the easiest rifle to set, its favourite pellet accuracy wise had to be put away because a heavy pellet i use to test would be over limit.
Turning down the power made the favourite go off.
Lastly don’t forget not to wind the reg in pressurised,backing off is ok though

 

[MrK]

Yeah i am not going to go to crazy low with it perhaps somewhere around 70-80 bar at first. But like you mention i need to know the base setting. I have a new lmbr chrono at the ready and aiming to keep it at 11 ftlb with 8.44’s ( 10.34’s at 11.4 ) as it is now untouched. I have a variety of different pellets to run through it also. I think the most attractive thing about it for myself at the moment will be having the convenience of a dedicated bleed valve and not having to mess with the manometer ( which gives me the heebie-jeebies a little if im honest ) or having to dry fire it to empty the plenum. Thankyou for the pointers

 

[MrK]

If it all gets a little to involved for my liking and not going the way i would prefer i might look into perhaps packing the plenum using delrin to negate the added volume but in such a way i can still retain the bleed and manometer fitting

 

[Owain]

I would set the reg to 55-60bar to start with. That seems to be the sweet spot with the HP. 45 and below would be considered low and may cause issues. The volume of the HP plenum is near optimal for reg/EV function on sub 12 setups.
Setting at 11fps with 8.4gr would make mine borderline with 10.3gr. I think it’s better to set it up with the heavies but that is what I use in my rifle.
Look up the 5bar test to set the reg.

Thread 'Lane 5 bar step'

Sep 15, 2022

Disclaimer : I failed me 11+ and therefore I am not qualified to to tell you any of this. Anything I write is uneducated waffle and you use it at your own risk. I will refund you all the money you paid me for this information if I am wrong

Lane videos are here for setting up a regulated gun and pellet choice, also worth reading the the Sterne articles for a good explanation of how a PCP works.

The Lane 5 bar step is used to determine the ideal operating pressure (IOP) for a gun in a given tune using very little air and a small number of pellets. The IOP is the...

• sagalout
• Replies: 90
• Forum: Airgun Technical & Diy Repairs

• 

 

[MrK]

^ @Owain i am definitely onto this did a full string shootdown from 150 bar and recorded mv unfortunately due do a combination of innacurate and unrefined gauge on gun and my eyesight i deemed it impossible to note Bar.I think i have nailed down the plateau and the drop off somewhere around 70-90ish Bar. Highest fpe averaging 11.3fpe using 10.34’s for half dozen shots or so before the mv started falling. I think i can narrow this down more accurately now using a stirrup pump connected to the gun ( it only dawned on me after the fact ) other than that i will be ordering a digital test gauge.

 

[MrK]

To add this is with standard plenum to get my base setting.

 

[MrK]

Ok. Equiped with a 28mm wika gauge i went ahead and fitted the hp plenum earlier. My base plenum pressure with standard plenum was 80 bar. Fitted the hp which satisfyingly happened with little drama. Tried 60 bar which shot comfortably but spiking when coming off reg same with 55 bar and ended up at 50 where it smoothly dropped off. With hammer adjustment now running around 11.2 with 10.34’s. Mine has a solid barrel with a transfer port a little different than standard maybe this affects my findings. Interestingly both pre and after hp plenum i only get a difference of around 0.4fpe between 10.34’s and 8.44’s.

 

[MrK]

I just need to sort the hammer guide/adjuster now. Brass “ dust “ contamination down through to the trigger sear and turns a little to easily for my liking.

 

[Quentyn]

I just need to sort the hammer guide/adjuster now. Brass “ dust “ contamination down through to the trigger sear and turns a little to easily for my liking.

The lockring and stainless hammer rail from sub12 airgunners on YouTube / eBay works flawlessly

 

[MrK]

hi all. Just ran a shot string to narrow my results down again and reg at 50 bar yet mv actually starts falling at 40 bar cylinder pressure??? ( down to 9.3fpe in 7 or so shots ) would i expect any problems setting reg that low? Think i may need to take a little break then approach it again i am surrounded by masses of note pad scribblings

 

[MrK]

My mistake it actually starts falling at 50 as i originally thought. However my shot to shot constistency appears slightly worse than with the standard plenum accross 10.34 and 8.44’s. Fun being able to shoot down to 50 bar though jury’s out at the moment i think with the hp plenum it may require somebody with a bit more skill than myself to tune things to there best.