Power fluctuation

[Jamie1722]

Hi all
What would be an acceptable power fluctuation between shots or several shots. im getting around 1 to 1.5 feet pounds until the pressure is between 180 and 150 bar,then it settles and becomes less of a variation i have a mk 1 rapid on fast flow
Thank you   

[angrybear]

Sub 12 or FAC (cal & power)
I always prefer to go by velocity & consider 5% extreme spread to be acceptable, 3% good, 2% very good, & 1% exceptional.

[KevG]

need more information but if sub 12 ftlbs don't fill higher than 170-180 bar
kevG

[Jamie1722]

Hi Kev
Thank you for your reply,150 to 180 seems to be its sweet spot ive also been toying with hammer springs and guides as well as different grains of pellet am i right in thinking its trial and error and what would you consider a large variation to be a problem
Kindest regards
Jamie

[Millingman]

Get a reg from Kevg for your Mk1, you won't regret it if it's consistency your wanting with spreads. Kev will keep you right.

[Jamie1722]

Sub 12 or FAC (cal & power)
I always prefer to go by velocity & consider 5% extreme spread to be acceptable, 3% good, 2% very good, & 1% exceptional.

thank you for your reply sub 12 .22 i will take your suggestion and try it out many thanks again
Kind regards
Jamie

[Jamie1722]

Get a reg from Kevg for your Mk1, you won't regret it if it's consistency your wanting with spreads. Kev will keep you right.

thank you for your reply a reg would sort it but im having fun messing around lol if i cant get it a kevg will be on the cards
Thanks again
Kind regards
Jamie

[angrybear]

thank you for your reply sub 12 .22 i will take your suggestion and try it out many thanks again
Kind regards
Jamie
[/quote]

If bought used it could be a previous owner was running it hot with a larger valve & port, which I believe cause a wider power fluctuation.

[Jamie1722]

thank you for your reply sub 12 .22 i will take your suggestion and try it out many thanks again
Kind regards
Jamie

If bought used it could be a previous owner was running it hot with a larger valve & port, which I believe cause a wider power fluctuation.
[/quote]yes  ah maybe thank you

[KevG]

you need to check the barrel porting.for sub 12ftlbs it's should be 4mm narrowing down to 3mm were it enters the bore.valve body front port should be 5mm,if its .22 calibre the bottle adaptor should not have an hole on the holding thread relief
kevG

[Squinty]

1 to 1.5 foot pounds spread.. not good with the same pellets but changing from light 14gr to heavy 18/21gr..possible within the bounds normal shot to shot variation.
Heavy pellets tend to be more efficien, si you can get 0.5 to 0.75 fpe variation between light and heavy.

As already suggested if you have a narrow plateau/sweet spot ie 180>150bar with 40-60fps spread the valve and porting are one of the first things to check.

Check the length of the hammer pip, should be 16-17mm.
Shorter is often a sign of over enthusiastic tuning.
The hammer should be clean and free of grease, same goes for the hammer bore in the block.
Grease will make the hammer skip and throw up inconsistencies.
Also that the pip is tight, that the inertia weight is fitted and the spring isn't mangled.


should shoot from 180 bar down to 100bar? with 20-25fos spread at the min-max.

If the output is pressure dependent
chopping and changing springs won't really help.
You'll have lots of fun shooting over a chrono but ultimately start to pull your hair out.

I'd say put in a new valve- a decent one with the right size ports and work back from there.
You can negate some potential over porting with flow control, can be a bit sensitive, a narrow band of adjustment but doable with some tweaking.

[Jamie1722]

1 to 1.5 foot pounds spread.. not good with the same pellets but changing from light 14gr to heavy 18/21gr..possible within the bounds normal shot to shot variation.
Heavy pellets tend to be more efficien, si you can get 0.5 to 0.75 fpe variation between light and heavy.

As already suggested if you have a narrow plateau/sweet spot ie 180>150bar with 40-60fps spread the valve and porting are one of the first things to check.

Check the length of the hammer pip, should be 16-17mm.
Shorter is often a sign of over enthusiastic tuning.
The hammer should be clean and free of grease, same goes for the hammer bore in the block.
Grease will make the hammer skip and throw up inconsistencies.
Also that the pip is tight, that the inertia weight is fitted and the spring isn't mangled.


should shoot from 180 bar down to 100bar? with 20-25fos spread at the min-max.

If the output is pressure dependent
chopping and changing springs won't really help.
You'll have lots of fun shooting over a chrono but ultimately start to pull your hair out.

I'd say put in a new valve- a decent one with the right size ports and work back from there.
You can negate some potential over porting with flow control, can be a bit sensitive, a narrow band of adjustment but doable with some tweaking.

thank you looks like more fun to had i will take on board waht you have said as with all the others see what i can do many thanks for yoyr time
Regards
Jamie

[KevG]

by rights if gun is ballanced and set up right power should start at around 11 ftlbs climbing to around 11.7 ftlbs of course it depends on your fill pressure but rule of thumb 170 to 180 bar.
kevG

[rgc_swanseaARC]

+1 for the adding a reg mod, when you have ruled out all the other possibilities.
Un-regged guns can be very accurate and consistent, but once you fit a reg you take away a lot of the variations and in theory gain inherent accuracy.
I used to do HFT with an Air Arms MPR-FT. (un regged)
Epic rifle. 
I got Simon to drop one of his regs in it and it went from amazing to the stuff of legends. 
I've had some very good and consistent rifles before and after, but nothing that came close to that.

Once you are sorted with the porting and the hammer balancing, id definitely recommend looking into a reg.

Kind Regards,
Rhys

[Millingman]

Thats what one of Kevg's regs can do on a mk1 when tuned properly. Like Kev says its a balancing act between porting, hammer spring, valve spring and pressure. If you have consistent air pressure it's half the battle. Check your pellet probe isn't leaking air, that can also cause problems.