Inconsistent FPS, Accuracy & Range

Discussion in 'Gun Building, Modifications & Repairs' started by OutlawAirsoft, Jan 20, 2021.

  1. OutlawAirsoft

    OutlawAirsoft Active Member

    108
    30
    Hamilton
    Hey all,
    I have an issue with my ICS AK (again). Basically, every other shot drops fifty feet from the muzzle (as if their is not enough hop-up, but worse), the other shots don't even leave the barrel (as if their is way too much hop-up), and every fifth or so shot shoots perfectly.
    I have tried various hop-up packings and nubs, including custom flat-hopping, Maple Leaf hop-up MR 50, and stock ICS, but nothing changes the performance. I have popped the gearbox open, and can't see any issue. The piston head I am running is a Maxx aluminum one, double O-ringed. At first I thought the air seal was inconsistent due to the piston head, but couldn't repeat the problem.
    In addition to the range and accuracy variances, the FPS seems to jump around dramatically. It also sounds like the air nozzle is stopping in a different spot after every shot, and therefore the length of time it takes to cycle changes.
    Any advice would be greatly appreciated.
    Thanks in advance, OA.
     
  2. Jeranhound

    Jeranhound Active Member

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    Seattleish
    It sounds like the only part you haven't tried changing are the tappet and nozzle. An off-length nozzle can cause all sorts of havoc with your shots.
     
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  3. OutlawAirsoft

    OutlawAirsoft Active Member

    108
    30
    Hamilton
    The nozzle is stock and the tappet plate has been replaced, but it worked fine months ago. I am at a loss here.
     
  4. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Stock barrel? Or an after market barrel? Sounds like a bad crown on a barrel.
     
  5. BeansOnToast

    BeansOnToast Active Member

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    Seattle
    Kind of straying from the topic but I've been getting inconsistent feeding problems from a gun I just got, all stock. Its an EMG F1 if that helps. (Great, another superb APS product.) (Should I make this its own thread?
     
  6. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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  7. OutlawAirsoft

    OutlawAirsoft Active Member

    108
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    Hamilton
    It is the stock barrel. I thought that could be a cause, so I rolled it on a granite counter top. It does seem slightly off (rolls with a bit of a wobble), but I didn't think that was enough to affect the performance like that. I thought a bent barrel affected it at least somewhat consistently.
     
  8. Aviglakis

    Aviglakis New Member

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    Billings
    I had an issue with ICS and aftermarket cylinder heads, the fit was off just enough to allow the cylinder head to flex in its places causing extremely inconsistent airseal between the nozzle and bucking. It would cause sometimes zero pressure and sometimes just enough to poop a bb out, and other times it was perfect. I switched back to an ICS cylinder head. My FPS is +-1.2 so it appears to be doing it’s job.
     
  9. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

    7,437
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    Most stock parts do...most aftermarket parts is becoming less and less so of an "upgrade".
     
  10. OutlawAirsoft

    OutlawAirsoft Active Member

    108
    30
    Hamilton
    Hey all, I am still having trouble with my AKS-74. Basically half the shots drop significantly and travel very slowly, while another half basically shoot straight down, as if my hop-up is set too high. Only one in 5 or 6 shots travels normally.
    I had this problem before, and have tried flat hopping it, and am currently running a MR 50 Maple Leaf w/ a hollow nub. It doesn't seem to make a difference. The air nozzle is stock but the tappet plate was replaced about a year ago, but it worked fine for a while after that.
    An odd thing I noticed was the packing lip was sticking into the feed tube about 3/4 of a millimeter, or around 1/32 of an inch (these are estimates, it was only barely enough to keep BB's from free falling all the way to the bottom when the gun was turned upside-down). I don't know if that has anything to do with the issue, but it didn't look normal. In addition, the air nozzle is still stopping in different spots.
    Any help would be great.
     
  11. Peeque

    Peeque Well-Known Member Supporting Member

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    Lancaster
    Are you able to change back to the stock piston head or different one? Maybe your issue is similar to Aviglakis's.

    The packing sticking out a tiny bit shouldnt be a problem. I've found the ML packing lips to be a tad longer than others. I use their packings in a few of my AEG's and they all stick out about as far as you described. It's not ideal though.
     
  12. OutlawAirsoft

    OutlawAirsoft Active Member

    108
    30
    Hamilton
    I tried other piston heads, and couldn't get different results. Plus, I've had this one in for a while, and it has worked till recently.
     
  13. Peeque

    Peeque Well-Known Member Supporting Member

    854
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    Lancaster
    Have you tried the paper test?
     
  14. richman992

    richman992 Well-Known Member

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    Rochester
    Did you at any point change your sector gear or remove the delay chip? This sounds like a tappet timing issue from my limited experience.
     
  15. OutlawAirsoft

    OutlawAirsoft Active Member

    108
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    Hamilton
    No, but the tappet plate is after market. However, it used to work perfectly.
     
  16. Peeque

    Peeque Well-Known Member Supporting Member

    854
    476
    Lancaster
    Clean out the cylinder and the piston head then apply some grease. Maybe your piston head isn't sealing with the cylinder anymore.
     
  17. Ben3721

    Ben3721 Well-Known Member

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    This sounds like a packing/nozzle issue to me. I've worked out this exact issue on a few guns.

    From what I've found nozzle tips and packing lips can be tapered, this prevents packing lip folding and jamming. You can't have a flat tip nozzle and a untapered packing inner lip, it will just cause all sorts of madness. It needs to go into the lips then push the lips outwards to seal, not flat on crush them inwards causing them to snag or jam the next bb.

    Some nozzles are also wider than others. A narrow nozzle will tend to be pushed up and snag the top of the packing lip, too wide and it won't move freely. Some are wider on the back, which snags up on some hop up chambers, or prevents it from moving all the way forward.

    Some hop up units fit loosely in the front gearbox hole, that slack snags the nozzle and causes feeding issues, which can make wild shots.

    Another common issue is packing lip folding from the lips protruding into the hop up feed tube. This typically will work in semi auto then misfeed and jam in full auto.

    Its not just one single part to blame, its how randomly designed parts fit and work with eachother.
     
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