Featured Shim M4 Gearbox for Nozzle Alignment

Discussion in 'Gun Building, Modifications & Repairs' started by DasJokerchen, Jul 19, 2021.

  1. DasJokerchen

    DasJokerchen New Member

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    Hey guys,

    I've got a small problem with my Cyma SR25 and seek your help to fix this...
    The alignment from nozzle to bucking seems to be off. When I look down the inner barrel I can clearly see the two circles (bucking and nozzle) but the nozzle is not centered. It sits too high and a bit to the left which is probably the reason for the bad groupings I am getting out of this gun.

    I was thinking that this picture itself could have multiple causes:
    - Nozzle at an angle (bad manufacturing, faulty angle at cylinderhead etc)
    - HU unit at an angle
    - Gearbox at an angle

    However, I am not able to move the HU unit when it sits in the outer barrel and I get the same (very same) picture when trying it with a whole new barrel/HU unit setup. Thats why I don't think it's the HU units fault.

    Now i am tying to figure out what to do next.
    The chrono values are pretty consistent (~4fps deviation).
    I also had some problems with midcap syndome and lathed a chamfer on the nozzle (better fitment to bucking, at least that was my plan) and shortened the tappetplate spring by a coil. The misalignment already existed before I did these modifications.

    I am now thinking about shimming the whole GB. Has anyone tried this before or any different ideas?
    Hope you guys can help me out here

    My setup:
    Cyma SR25 (V2.2 GB)
    Maxx HU unit
    ML MR bucking 60°
    EpeS Nozzle 24,9mm
    FPS Cylinderhead
    Promy inner barrel 6,03mm
    Retro Arms Type 0 Cylinder (SR25)
     
    Last edited: Jul 20, 2021
  2. Ben3721

    Ben3721 Well-Known Member

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    I would first remove the slack around the inner and outer barrel. Also if the hopup unit is firmly locked into the gearbox front shell hole it can't move side to side or up and down independently. However if the outerbarrel or front of the upper receiver is off or bent it will kink the connection of the hopup unit and gearbox, causing this issue. Make sure the gun is straight.
     

  3. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    There is a degree of float and it's really not the main issue of your accuracy.

    Nozzle and hop-up does not have to be perfectly lined up. In fact this would be more of a feed issue and your not having that issue.

    Rather your issue may be the MAXX unit. With the lack of standards in Today's Airsoft this could be the issue.

    With that...describe what accuracy issue you are having? What brand of bbs are you shooting and at what weight.

    The key to accuracy by biggest factor in this order is:

    BB Type and Quality
    Rubber/Packing/Bucking
    Barrel

    Nozzle alignment is not a major factor in this case...now if you were having a feeding issue...then what you described above is very relevant info.
     
  4. Ben3721

    Ben3721 Well-Known Member

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    I just realized it was a Maxx hop up unit. While they are pretty, and have a great hop up arm system and dial, their feed tubes are like 8mm all the way up. It also has a design flaw inside the feed tube that snags the pellets as they move up, it's offset accidentally. Some get them to work, others have a similar experience. It just doesn't hold and center a nozzle correctly and let's the bb sit anywhere before being feed in.
     
  5. DasJokerchen

    DasJokerchen New Member

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    Wolfsburg
    Thank you for the suggestions!
    First of all I have to say that I've tried it with the stock HU unit as well (with different bucking and barrel) and still got the same picture when looking down the barrel. So that's why I figured that it's most likely not the Maxx unit.

    I also did a different experiment:
    I took the lower body with the GB installed and pressed the HU unit firmly against the shell like it would sit in a complete gun. The picture was still the same so it's probably not the way the HU unit is sitting in the outer barrel as well. Same picture with the other setup (other hu unit, bucking, barrel)

    I do not have feeding issues and never had with this gun

    The shots are very inconsistent. While my fps are more or less consistent (+/- 4 fps) the BBs fly to the left, to the right, lower or higher. Most of the times the left/right fliers are flying in curves rather than straight. If it shot 10 BBs at once you might think that it's a sawed off shotgun

    I shoot with .33g BBs and a volume ratio of 2.4:1. Ported cylinder, AOE corrected and 407mm inner barrel. I use the aluminum nub from Maxx (came included) as I found that it gets slightly better results than an Omega nub
     
    Last edited: Jul 19, 2021
  6. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    You are shooting G&G .33g bbs?

    Well...The barrel could be too tight and you are suffering from barrel turbulence.

    I am not seeing the bb size info...but if your gap between bb and bore is less than .08mm...it's too tight.
     
  7. DasJokerchen

    DasJokerchen New Member

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    Wolfsburg
    I just noticed:
    When I press the HU unit (with barrel etc) fimly against the gearbox itself then the nozzle is off as well!
    It's not the positioning of the gearbox then but the nozzle, cylinderhead or tappetplate that misalignes the nozzle

    Yes, I shoot .33 G&Gs, forgot to put in the brand
     
  8. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Does your bag cite the BB bore size?

    As noted earlier the nozzle can float. This is a good thing...last thing you need is a system that has to be "perfectly" aligned and if that doesn't happen you start snapping off AEG bits...
     
  9. DasJokerchen

    DasJokerchen New Member

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    The BBs have a diameter of 5.95mm

    Why is it bad if everything is perfectly aligned? In a VSR you'd want that too
     
  10. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    A VSR is a very different creature. The structure is supported by the BASR body tightly.

    An AEG with mechbox has none of this support and thus the float allowed is okay to have fior the mechbox is technically floating inside the receiver and is only aligned by a pin or two on some models.

    Bad? That is a subjective question. It's not easily achievable when the industry has no standards.

    In an AEG when you are mix and matching parts, this feat is near impossible. And your accuracy issue...is not due to the nozzle not aligning perfectly with your hop-up unit.

    All that nozzle needs to do is push the bb into the hop-up and focus the pressure wave into the barrel. If it does that...it's fine.

    I am surmising you may have a dirty barrel...how do you clean your barrel?
     
  11. DasJokerchen

    DasJokerchen New Member

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    Wolfsburg
    Hmm I understand what you are saying but it still should deliver better results if I can align everything "perfectly ", right?

    I tried different buckings and nubs but it's still not shooting straight...

    I cleaned the barrel right before I tested everything with the cleaning rod, some tissue and alcohol. I made sure to turn the hop off and didn't damage the patch. The barrel shines like jesus's holy grail and is perfectly straight (also tested it)
     
  12. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Nope...it's behind the threshold of bb flight.

    Once the bb is in the packing and the air is delivered to create the pressure wave, any alignment behind it is not a major factor on bb accuracy.

    But, back to your barrel...I would check the crown for damage now that you clarified your barrel is squeeeky clean.

    Also, do you have a caliper, if you do, can you mic your bbs? Now and then a bad batch of bbs gets out even under G&G's QC criteria.

    Do you have other bbs to test? What range are you testing at...and your not doing this outside are you?
     
    wetpee likes this.
  13. wetpee

    wetpee Active Member

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    Your FPS deviation seems pretty standard for a RIF with good enough airseal. What's your muzzle energy like with various BB weights?
    Guges is leading you down the right path he knows his stuff. Nozzle alignment may be an issue for HPA systems, but they also don't have the same design as AEG where the tappet plate design can allow the nozzle to float (center itself). The way the air or the amount of air is delivered may also play a factor for HPA. Also, I imagine more intense ROF builds like DSG may require more meticulous tuning than relatively standard AEGs to correct the tolerance, QC, and design limitations (beyond needing more durable parts for reliability) that typical manufacturers aren't worried about satisfying.
    Check your BBs, then, make sure the hop contact patch isn't hanging up on anything. I've experienced a prommy EG barrel's window not being cut wide enough for an ML super mac, but the MR is quite different since it ideally fills the whole window and the patch is connected to the stabilizing points that rest on either side of the window.
    With regards to your "midcap syndrome": Did this exist in 100% stock form? What mags? Definitely do hop unit drop tests if you haven't done that already when you run into feeding issues. I reluctantly decided to shave down the breech end of a barrel because the hop packing I wanted to use wouldn't allow the cuts for the c-clip to line up and forcing everything together would cause the packing to bulge into the feed tube and prevent all semblance of reliable feeding, but could sometimes feed and many times shoot like poo with super low FPS when a BB did come through. Since then, I've done this twice more. 2 stock CYMA barrels (platinum MP5 and plat SR25) and some cheapo full ABS receiver tippman or similar sportline M4. That thing's gotta be pretty old I think my buddy got it at a pawn shop lmao. All stock brass barrels with otherwise 100% stock internals except a stiffer spring on the MP5 for rifleman muzzle energy. I don't know if this is the best way to address this, but its worked well for me and using different nozzle lengths or shaving down packing feed lips doesn't sit well in my head. I want my stuff to seal the way its designed to and I felt I could get that breech end flat enough. I was shooting lasers with the MP5 last week on maple leaf super mac on .3g BBs. Chrono'd at ~1.25j on .2 or .25g. No recollection of FPS deviation. Second time taking it out, first time since the modifications. Original readings out of the box were ~310-314FPS on .2g. The SR25 I haven't gotten any reports back about yet -- didn't have a mag to chrono with. The unknown ABS receiver M4 set for 1.1j indoor on ML super mac and the guy used it outdoor and was fully impressed at his range and accuracy and the chrono guy was flabbergasted at how it was shooting so consistently.
     
    Last edited: Jul 20, 2021
  14. DasJokerchen

    DasJokerchen New Member

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    My initial thought was that the nozzle created small air leaks as it is going into the bucking in an angle. Thus creating inconsistencies in the airflow...

    The crown is looking fine

    I measured a few BBs with a caliper and found that they are all 5.94 - 5.95 mm in diameter.
    I chronoed with .2g, .28g and .33g all G&G. At .2g the deviation was at about +/- 6 fps and it went lower the higher the bb weight was. At .33g I have +/- 4 fps. All pretty much standard. The cylinder seals perfectly too so I actually hoped for a little bit better results with the chrono as I thought the whole gun should seal well after all of my modifications.
    I don't have the muzzle energies at hand, would have to chrono it again but the gun is currently taken apart

    The range/accuracy tests were conducted outside on the shooting range at the last game. I used buckings, nubs, BB weights in different combinations while shooting about 80 BBs for every configuration to see how it performs. Wind was pretty much nonexistent and the distance was about 70m.
    I found that my current (see first post) configuration works "best" but still performed poorly in the game and at the range.

    The patch moves straight up and down, no observable problems here.

    I found out about the mid cap syndrome just after the last game (with the testings etc). It was the second game I played with the gun and I immediately modified it after buying. First game was also not great with it. So I don't really know how it'd have shot in stock condition.

    I've heared about having to shave down a bit from the barrel (especially with maxx units) because it can't handle buckings that well that have longer lips. But since I don't experience any feeding issues I have second thoughts about working on my promy barrel just to try something out... Also the C clip fits in kinda easily and the lips don't look bulged to me
     
    Last edited: Jul 20, 2021
  15. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    70M is a very long way off. Where is the drift you are noticing? 30M in front of the barrel or longer.
     
  16. DasJokerchen

    DasJokerchen New Member

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    Probably before the 30m mark. At 70m I'd hit within a 6m circle or so
     
  17. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Six Meters at Range???

    That is not something a nozzle is going to make your bb do...that...that is just bad spin on the bb.

    I would like to see a picture of your hop-up breech side looking in and down the barrel.

    Like this:

    [​IMG]
     
  18. DasJokerchen

    DasJokerchen New Member

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    Not sure if we misunderstood... If I shoot at 70m the BB would travel that far but only hit a 4-5m circle. The 6m were a bit over exaggerated
    Will send a picture when I'm home
     
  19. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Even 4-5M, that is a large deviation. Most people hit in at 2 meters or less at 70M for "stock" AEG and "tuned" AEG's hit at 1M or less.
     
  20. DasJokerchen

    DasJokerchen New Member

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    Wolfsburg