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inaccuracy issues


KiloGr
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Hi all,

 

At my wits end with this RIF.

CM16 SRL 12"

P* JACK

Tried ZCI, MAXX PRO and 5KU hop units

3 different barrels (currently 230 promethius 6.03

 

My problem is the bbs always hooking left badly and extremely bad inaccuracy.  I thought it was an alignment issue however even after fine adjusting and the nozzle and gearbox looking dead centre, they still ping off in every direction.

 

New buckings and nubs have been tried, hop units, barrels which i have cleaned, dwell is set properly and psi is consistent.

 

Have spent WAY too much on this build now and im getting really beyond frustrated with it.  I want it working or want it gone.

 

I need some more suggestions on what to try.  Tried new literally everything you can imagine.

 

Even took it to a tech and he couldnt figure it out said i need to leave it with him.

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Bent barrell?

 

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first suspect i'd be looking towards is the bb's clipping something on the way out, typically a suppressor but can be a bit of damage in the inner barrel (although in this case unlikely given you've swapped that out already)

 

it's not sounding like the typical jack issue which is inconsistent velocity/vertical spread.

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1 minute ago, Shamal said:

Bent barrell?

 

tried a few barrels and outer barrels, all the same

1 minute ago, Adolf Hamster said:

first suspect i'd be looking towards is the bb's clipping something on the way out, typically a suppressor but can be a bit of damage in the inner barrel (although in this case unlikely given you've swapped that out already)

 

it's not sounding like the typical jack issue which is inconsistent velocity/vertical spread.

tried it with my suppressor on and off, still get the same effect too unfortunately

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Sight alignment maybe?

I just got a Bore sighter and that is great for lining up sights.

 

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2 minutes ago, KiloGr said:

tried it with my suppressor on and off, still get the same effect too unfortunately

 

hmm, maybe the flash hider itself?

 

the way you're describing it sounds like you already know and have checked for the usual suspects but just for the sake of completeness the only thing you haven't mentioned specifically is checking the hop mound is centered in the barrel, and it's worth doing that over a range of hop settings as it can look fine on minimal hop only to deform when turned up further.

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4 minutes ago, Shamal said:

Sight alignment maybe?

I just got a Bore sighter and that is great for lining up sights.

 

i dont run sights, i look down the barrel and can see them pinging left as soon as they leave the barrel near enogh

 

1 minute ago, Adolf Hamster said:

 

hmm, maybe the flash hider itself?

 

the way you're describing it sounds like you already know and have checked for the usual suspects but just for the sake of completeness the only thing you haven't mentioned specifically is checking the hop mound is centered in the barrel, and it's worth doing that over a range of hop settings as it can look fine on minimal hop only to deform when turned up further.

So for the hop things, i have tried with multiple hops, barrels buckings and nubs.  All have had the same affect. Rebuilt them i dont even know how many times for the same thing to happen unfortunately.

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4 minutes ago, KiloGr said:

i dont run sights, i look down the barrel and can see them pinging left as soon as they leave the barrel near enogh

 

see that symptom is just screaming the bb clipping something, usually with a hop misalignment it'll go straight before curving off (like you were tilting the rifle constantly to one side)

 

it could also be a bit of dirt/damage at the end of the inner barrel, although the fact you've wholesale changed the barrel kinda discounts that notion (although worth checking regardless)

 

4 minutes ago, KiloGr said:

So for the hop things, i have tried with multiple hops, barrels buckings and nubs.  All have had the same affect. Rebuilt them i dont even know how many times for the same thing to happen unfortunately.

 

yeah, it's unlikely and doesn't sound like it fits the symptoms as per above, but i've had enough of them sneaky buggers misalign for no intelligible reason to not discount it as a possibility.

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Strange one for sure🤔 

Gotta be the hop, barrell or some kind of contact as BB leaves.

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That it's happening with multiple barrels (inner and outer) and hop units suggests looking elsewhere.

 

Are the hop units flush and square with the gearbox?  Is anything standing proud and tilting them?

 

What about the receiver around the hop unit?  Any ridges, bumps, or wallered out areas, or something jammed down one side of the slots that the hop unit keys into?

 

How are you tensioning the hop units against the gearbox?

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Have you tried using a different brand of BBs?

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  • 2 weeks later...

Is the nozzle centred correctly . Look down the barrel with flash light pointing up the hop hole. See if the nozzle is in the centre of the barrel ? If it isn't and to one side then more air will be pushing the side of the BB to move and curl that way 

 

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hi guys,

 

update : Nozzle alignment is good, gearbox isnt one sided and nothing is bent. 

 

Got a new prometheus 270 something barrel and new bucking + nub, the bb leaves straight but after about 20m some fly up, some fly down, left and right etc, super inconsistent past like 30-40m.

 

Brand new MAXX pro hop, brand new (now worn in) maple leaf 60 bucking and omega nub, dwell set and consistent PSI.

 

Really stumped now, considering selling for an MTW.

On 15/06/2022 at 09:30, Skara said:

Have you tried using a different brand of BBs?

hey!

 

Yes, i tried Valken, Valkyre, NUPROL (lol), ASG devil blasters.  Now its shooting straight its a tad innacurate

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1 hour ago, KiloGr said:

Got a new prometheus 270 something barrel and new bucking + nub, the bb leaves straight but after about 20m some fly up, some fly down, left and right etc, super inconsistent past like 30-40m.

 

is it worse in the vertical spread than the horizontal?

 

as a general rule horizontal spread is a function of the hop, and component alignment (eg barrel being wobbly, etc)

 

vertical is a function of both the above and your fps consistency.

 

i'm wondering if now what you're getting is the latter of those, specifically jack syndrome which i mentioned earlier.

 

to quickly run through the way the jack works:

1.default state is reservoir under pressure, pulling the nozzle rearward

2.a shot signal sends air behind the nozzle, pushing it forwards picking up the bb etc

3.when the nozzle gets to about 1-2mm from the end of travel a set of ports is uncovered

4.the ports allow air from the reservoir through the centre of the nozzle and down the barrel to push the bb

5.when the shot signal is over the air behind the piston is vented, the pressure in the reservoir now pushes the nozzle back

 

the issue is between 3 and 4- air is getting sent through the nozzle before the nozzle has gone full travel to seal against the hop lips, the randomness of escaping air is what's giving a variation in velocity and hence vertical spread.

 

if your symptom is vertical and not horizontal dispersion (or at least, a lot worse in the vertical than the horizontal) then that would be a likely candidate.

 

unfortunately there's not really a solid fix for this, it's an inherent design flaw of the jack and if you're building for long range accuracy the only option is to not use that engine. you want a closed bolt system, for polarstar's product line the 2 you want for accuracy work are the F2 and the fusion, with the f2 being somewhat more adaptable and easier to setup than the fusion. there's also the wolverine offerings although having never run them i can't comment as to their efficacy.

 

if it's about even horizontal/vertical then could be a dwell issue, too much or too little air, hard to call without seeing it but the above only applies if you're getting pretty solid dispersion horizontally but the vertical is going off.

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