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KM4a1 can't open receiver

KM4a1 disassembly receiver

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#1 AEGlee

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Posted 29 November 2013 - 06:29 AM

Hello,

I can't open my KM4a1 receiver.

The gun will not shoot at all, so it can't be dry-fired to make sure the piston is forward. Also the charging handle will not completely engage; it's about 3/8" short of latching.

The retaining pin has been removed and the upper receiver will pivot open about a 1/4", but then it stops and will not open farther, even with a lot of force.

I have searched this forum and others with no solution found, so any help would be appreciated.

Thanks.

#2 gcw360

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Posted 29 November 2013 - 10:20 AM

View PostAEGlee, on 29 November 2013 - 06:29 AM, said:

Hello,

I can't open my KM4a1 receiver.

The gun will not shoot at all, so it can't be dry-fired to make sure the piston is forward. Also the charging handle will not completely engage; it's about 3/8" short of latching.

The retaining pin has been removed and the upper receiver will pivot open about a 1/4", but then it stops and will not open farther, even with a lot of force.

I have searched this forum and others with no solution found, so any help would be appreciated.

Thanks.
Hi AEGlee - Welcome to the KWA Forums.  The charging handle not latching is most likely because the spring is overstretched.  You may need to replace the spring.  Or perhaps you can cut a coil or two off and reattach it the the handle.

Do not try to force the upper receiver open.  It will damage the piston.  The reason you can't open the upper receiver is due to the piston begin retracted (not fully forward).  When you try to fire the gun is there any sound at all?  Is the motor trying to turn and can't?  If the motor is not trying to move you may have a blown fuse or the motor connects may be off the motor terminals.  If the motor is trying to turn and the gun won't cycle, then you probably need a repair most likely due to a broken gear, bearing or piston....or a combination of the three.

To release the piston you need to do the following:
  • Remove the motor and grip from the lower receiver

  • Locate the anti-reverse latch.  This can be seen through the hole that the motor shaft normally goes through and it is engaging the bevel gear

  • Take a dental pick or some other tool and pull the ARL to release the tension in the gun.  There will be a snap as the piston comes forward
You should then be able to open the upper receiver.

Hope this helps and keep us posted.

#3 AEGlee

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Posted 29 November 2013 - 11:51 AM

@gcw360 Thanks for the excellent and quick answer!

I didn't know about the anti-reverse latch, which was the solution to opening the receiver. Thanks to you, it's open! That's one step closer to repairing my gun. If there are more questions, I'll surely know where to get the answers - here.

I didn't have a pick available, but a small allen wrench worked pretty well to release the anti-reverse latch.

If the repair is successful and would be helpful to this forum, I'll share it.

Thanks.

Edited by AEGlee, 29 November 2013 - 12:04 PM.


#4 gcw360

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Posted 29 November 2013 - 01:52 PM

View PostAEGlee, on 29 November 2013 - 11:51 AM, said:

@gcw360 Thanks for the excellent and quick answer!

I didn't know about the anti-reverse latch, which was the solution to opening the receiver. Thanks to you, it's open! That's one step closer to repairing my gun. If there are more questions, I'll surely know where to get the answers - here.

I didn't have a pick available, but a small allen wrench worked pretty well to release the anti-reverse latch.

If the repair is successful and would be helpful to this forum, I'll share it.

Thanks.
Thanks for the follow-up and feedback.  A paper clip cam work too, oh and love the avatar.

#5 Chuck S

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Posted 29 November 2013 - 03:53 PM

I keep telling my wife to stop posing for those photos...

-- Chuck

#6 gcw360

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Posted 29 November 2013 - 05:01 PM

View PostChuck S, on 29 November 2013 - 03:53 PM, said:

I keep telling my wife to stop posing for those photos...

-- Chuck
If you must....

#7 Jesse Hammil

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Posted 25 December 2013 - 07:30 AM

My ris does this semi regularly. It seems to do this when the battery starts to die. Changing the battery for a charged one fixes it.



#8 Jesse Hammil

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Posted 25 December 2013 - 06:17 PM

Maybe I have other issues....

#9 Chuck S

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Posted 26 December 2013 - 03:55 AM

I think this has to do with incomplete cycling.  Happened once or twice with my KM4-CQB, but not in a long time.

-- Chuck




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