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Bb's Droop On Full Auto


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#1 Anchor

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Posted 04 January 2012 - 01:37 PM

I just started to work on my MP9, I put a [barrel extension] adapter on it, and stretched the spring to have the bolt go back into battery. However, once I assembled it, I noticed: 1. My accuracy on rapid fire semi is worse than before and 2. the bb's don't fly at all after 3 rounds in full auto.

#2 niko_gpsy

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Posted 04 January 2012 - 02:54 PM

Can you verify if the bbs are not hitting the tip of the barrel extension? I am thinking the outer barrel swap left the inner barrel misaligned.

#3 Anchor

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Posted 04 January 2012 - 07:08 PM

I shined a flash light in the chamber, barrel looks to be in line with the adapter.

#4 niko_gpsy

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Posted 05 January 2012 - 08:52 PM

Have you disassembled your hop up while trying to install the new outer barrel?

#5 Anchor

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Posted 06 January 2012 - 12:11 AM

I have not, I simply went straight to the barrel swap, I kept the hopup/ inner barrel assembly intact.

#6 niko_gpsy

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Posted 06 January 2012 - 03:12 PM

Is the bolt operating normally?
And are the bb's jamming in the bucking or is it just not being propelled out of the gun?  Dry fire the gun and see if you can feel air coming out of the barrel.

#7 Anchor

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Posted 07 January 2012 - 05:03 PM

Yes, air is being pushed out the barrel. I'm gonna take it down, and see what I find.

Edited by Anchor, 07 January 2012 - 05:06 PM.


#8 niko_gpsy

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Posted 07 January 2012 - 05:44 PM

Maybe you have some feeding issue then.......

#9 Anchor

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Posted 14 January 2012 - 11:42 PM

Well, I've fired it with the adapter off, same issue. I'm wondering if I stretched the disconnector spring too much.

#10 gcw360

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Posted 15 January 2012 - 08:53 AM

Please answer the following questions:
  • Is the issues that the BB's are trailing off in full-auto?
  • Do you notice that the ROF slows a bit when this happens?
  • Are you dumping the entire mag?
  • How cold outside is it?
  • Have you chrono'd the shots to measure the drop in FPS as you go through the mag?


#11 Anchor

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Posted 15 January 2012 - 12:46 PM

1. The BB's are just dropping around 20 feet while the first 3 shots will fly just fine
2. Maybe a little, but not much
3. No, I'm firing 5 to 6 shot bursts
4. Temp can range anywhere from 60 to 65 degrees
5. I have not chronoed it.

I think this all may be due to the hop up.

However, now a new problem has arisen, the bolt won't push back the hammer. Or it fails to strike.  Essentially, it will just stop shooting, and I have to manually cycle the bolt to resume firing.

Edited by Anchor, 15 January 2012 - 12:47 PM.


#12 gcw360

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Posted 15 January 2012 - 12:54 PM

I would like to see a chrono reading as the BB's drop off.  Cold will cause a drop in performance, but it could very well be that the bucking is causing the issue.

#13 Anchor

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Posted 15 January 2012 - 01:17 PM

The other issue now is the bolt. Sometimes it just won't fire, I noticed this in full auto, and it happens sporadically. It just won't fire, I then have to re cock it and it will shoot fine.

#14 gcw360

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Posted 15 January 2012 - 02:06 PM

Can you show a picture of the spring you stretched?

#15 Anchor

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Posted 15 January 2012 - 03:11 PM

Posted Image

#16 gcw360

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Posted 15 January 2012 - 03:41 PM

Try a drop of silicone oil on the part the moves that is attached to the spring (towards the front of the gun).  Work it in manually and see if that helps with the bolt returning to battery.  Also, make sure the bolt is lubed too where it makes contact with other parts.  Do not over lube, just be sure it's not dry.

#17 niko_gpsy

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Posted 15 January 2012 - 05:51 PM

That spring looks stretched too much. All you needed was a slight stretch using a screw driver.

#18 Anchor

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Posted 21 January 2012 - 09:13 PM

Update: Ordered a new disconnector spring, and just put it in. From what I can, tell that fixed it. I will have more conclusive testing tomorrow.




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