Bucking / Nub combo?

[KiloGr]

Which bucking and nub would be the best for me?  HPA P* Jack and Maxx pro hop.

Using maple leaf ast maacaron 60 deg and maple leaf aeg solid hop tensioner at the moment

ARP9 base.  Groupings WHACK but putting this down to short stubby barrel (or is it...)

TIA

 

[Steveocee]

In my jack build I use a PDI W-hold 50. It just works well and will happily flick anything from 2's up to 36's (and likely heavier, I just haven't tried heavier yet).

PDI barrels you have to be a bit careful as the cutout isn't huge but any of the "old guard" such as a W hold, G&G green, Prommy purp should do the job really well for you.

Make sure the barrel is clean and that your dwell is set about right.

 

[Adolf Hamster]

macaron 60degree is a solid choice of hop rubber, and best paired with their "omega" nub, although the Rhop block on the maxx works equally well.

barrel length might be a factor, the arp is on the shorter end of things but tbh i'm tempted to say this might be open-bolt syndrome.

 

[KiloGr]

In my jack build I use a PDI W-hold 50. It just works well and will happily flick anything from 2's up to 36's (and likely heavier, I just haven't tried heavier yet).

PDI barrels you have to be a bit careful as the cutout isn't huge but any of the "old guard" such as a W hold, G&G green, Prommy purp should do the job really well for you.

Make sure the barrel is clean and that your dwell is set about right.

Got my dwell to about 29 before i started losing FPS (losing from 28 down), upped and left at 30, running 40rps nicely.  stock arp9 barrel was running 3s on about 85PSI, stuck a 300mm barrel in and had to try and run 45 psi which kept pissing out air with 32s.

Should i put the stock barrel back in and run 3s with a prommy purple?  What about the nub?

macaron 60degree is a solid choice of hop rubber, and best paired with their "omega" nub, although the Rhop block on the maxx works equally well.

barrel length might be a factor, the arp is on the shorter end of things but tbh i'm tempted to say this might be open-bolt syndrome.

it is the omega nub im running, should have mentioned.

I spoke to another arp9 owner and they said they got the same range from their 124mm barrel they did with a 280, which is similar to me.  Hop has to be on about 5 before it hops anything, which is why i thought the bucking was too stiff (60deg)

I think im going to put stock barrel back in and run 3s again on 85psi, i dont want to have ot buy 36s just to use a longer barrel for the same range and grouping.

might therefor get a prommy purple which is about a 50 deg right?

Is the lower the degree softer or harder?  And should i try a new nub? so i dont have to run 5 hop before it does anything?

 

[Steveocee]

Dwell at 30 with a 300mm barrel is far far too low. I'm running mine at 45 with a 208mm 6.05 for comparison.

Barrel length won't affect your range or grouping. 

Sounds like you're undervolumed if anything but yeah if you're halfway up the hop scale before it hops, your rubber is too hard.

 

[Adolf Hamster]

I spoke to another arp9 owner and they said they got the same range from their 124mm barrel they did with a 280, which is similar to me.  Hop has to be on about 5 before it hops anything, which is why i thought the bucking was too stiff (60deg)

tbh how far the actual hop wheel needs to go to get usable hop is less important than how much the hop bucking is impinging on the chamber, as long as there's some room either side of the "sweet spot" to adjust if needed (ie it's not spacing stuff with the hop completely off nor struggling to lift at full hop).

Is the lower the degree softer or harder?  And should i try a new nub? so i dont have to run 5 hop before it does anything?

lower degree is a softer grippier rubber, although the material also plays a part.

but i don't think the bucking/nub choice is the problem here as opposed to the nozzle alignment. the open-bolt nature of the jack makes it very sensitive to proper placement and fundamentally limits what you can get out of it due to the way the system works.

 

[KiloGr]

tbh how far the actual hop wheel needs to go to get usable hop is less important than how much the hop bucking is impinging on the chamber, as long as there's some room either side of the "sweet spot" to adjust if needed (ie it's not spacing stuff with the hop completely off nor struggling to lift at full hop).

lower degree is a softer grippier rubber, although the material also plays a part.

but i don't think the bucking/nub choice is the problem here as opposed to the nozzle alignment. the open-bolt nature of the jack makes it very sensitive to proper placement and fundamentally limits what you can get out of it due to the way the system works.

havent fixed the outer barrel issue yet i posted about the other day (Twisted outer barrel).  just below 6 is the sweet spot for .6s, so im fine on that front.

Will have a play and reset the dwell, start at 99 and work down until sweet spot found.  I worked down from 40 before, so thats my problem there.

Will fix twisted barrel so it shoots straight, then figure out what else the issue is

Dwell at 30 with a 300mm barrel is far far too low. I'm running mine at 45 with a 208mm 6.05 for comparison.

Barrel length won't affect your range or grouping. 

Sounds like you're undervolumed if anything but yeah if you're halfway up the hop scale before it hops, your rubber is too hard.

Im still new to all this, what would a higher more tuned dwell do?  More consistent?  Would this allow me to shoot at higher PSI as unless i  switch back to my 124 barrel i must run 45 psi on .32s else i shoot hot

 

[Adolf Hamster]

Im still new to all this, what would a higher more tuned dwell do?  More consistent?  Would this allow me to shoot at higher PSI as unless i  switch back to my 124 barrel i must run 45 psi on .32s else i shoot hot

the dwell time (dp) on the jack is the cycle time, when you pull the trigger the solenoid engages, air starts flowing, the nozzle moves forward and loads a bb then at near full extension air starts going through the nozzle to push the bb down the barrel. when the cycle is over the solenoid turns off, air stops flowing and the nozzle automatically retracts.

if the dwell is too short then it'll stop sending air before the bb has left the barrel, making it undervolumed and messing with accuracy

likewise if the dwell is too long then it'll keep sending air after the bb has left the barrel and the burst of following air can mess with accuracy (and also be a waste of air in general)

hpa's are particularly sensitive to having the voluming set just right, although at least adjusting it is relatively easy. the jack in particular (as you're finding with the longer barrel) is tricky as it's an entirely pressure fed system, so running a lower pressure also lowers the force the nozzle can move with meaning it'll struggle to chamber a round on a full mag.

 

[KiloGr]

the dwell time (dp) on the jack is the cycle time, when you pull the trigger the solenoid engages, air starts flowing, the nozzle moves forward and loads a bb then at near full extension air starts going through the nozzle to push the bb down the barrel. when the cycle is over the solenoid turns off, air stops flowing and the nozzle automatically retracts.

if the dwell is too short then it'll stop sending air before the bb has left the barrel, making it undervolumed and messing with accuracy

likewise if the dwell is too long then it'll keep sending air after the bb has left the barrel and the burst of following air can mess with accuracy (and also be a waste of air in general)

hpa's are particularly sensitive to having the voluming set just right, although at least adjusting it is relatively easy. the jack in particular (as you're finding with the longer barrel) is tricky as it's an entirely pressure fed system, so running a lower pressure also lowers the force the nozzle can move with meaning it'll struggle to chamber a round on a full mag.

Exactly the response i was after, thank you!

I think im going to fix my barrel issue then put the shorter inner back in, tune my dwell again, hopefully groupings should be a bit more consistent than 20m or so then flying in every direction known to man.