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Low fps drops


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#1 Cashman1501

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Posted 15 June 2012 - 04:35 PM

Hey guys i just bought my lm4 and its working great and functioning awesome but i have a question about something. When firing with .3 bioval and .28 bbs i sometimes find that the fps drops on a few shots then shoots fine again. Its pretty random but it seams to do it a few times each mag. Iv cleaned the barrel, hop up, and lubed some internal parts that have metal on metal contact. Its not a huge problem but i just want to know if it will work itself out after more use. Thanks

#2 Jatodude

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Posted 15 June 2012 - 04:41 PM

View PostCashman1501, on 15 June 2012 - 04:35 PM, said:

Hey guys i just bought my lm4 and its working great and functioning awesome but i have a question about something. When firing with .3 bioval and .28 bbs i sometimes find that the fps drops on a few shots then shoots fine again. Its pretty random but it seams to do it a few times each mag. Iv cleaned the barrel, hop up, and lubed some internal parts that have metal on metal contact. Its not a huge problem but i just want to know if it will work itself out after more use. Thanks

The problem is probably part number 191, the piston O-Ring.  It's loosing compression.  You could try to replace it, or send it back to KWA.  It's happened to quite a few people.  The problem is remedied by installing a slightly larger O-Ring for better compression.

These two O-Rings where recommended
35/64" x 23/32" x 3/32" hnbr (hydrogenated nitrile butadiene rubber)
Number 10 Danco

Edited by Jatodude, 15 June 2012 - 04:43 PM.


#3 Cashman1501

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Posted 15 June 2012 - 05:34 PM

Ok well where could i find one of those. Im an experienced gun tech but how hard would u say it is to get to the piston?

#4 Jatodude

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Posted 15 June 2012 - 05:42 PM

View PostCashman1501, on 15 June 2012 - 05:34 PM, said:

Ok well where could i find one of those. Im an experienced gun tech but how hard would u say it is to get to the piston?
Hardware store or something like that.

Here's a guide that will show you how to take out the piston: http://kwausa.com/fo...?showtopic=8778

#5 Cashman1501

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Posted 15 June 2012 - 06:30 PM

Thanks man, that realy helps! Iv probably shot 500 rds or so through it total so ill see if it continues to have that problem but hopefully it will get better. About 5,000 rds is what it takes to break the weapon in right?

#6 gcw360

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Posted 15 June 2012 - 08:20 PM

Home Depot and Lowe's will carry that o-ring (#10 Danco).  Niko has already made the swap and I am doing so this weekend.  More to come later.

#7 Nitemare

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Posted 16 June 2012 - 12:22 AM

Is removing/placing an o-ring difficult? Seems like it could be depending on the tolerances.

#8 niko_gpsy

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Posted 16 June 2012 - 04:41 AM

View PostJatodude, on 15 June 2012 - 04:41 PM, said:


The problem is probably part number 191, the piston O-Ring.  It's loosing compression.  You could try to replace it, or send it back to KWA.  It's happened to quite a few people.  The problem is remedied by installing a slightly larger O-Ring for better compression.

These two O-Rings where recommended
35/64" x 23/32" x 3/32" hnbr (hydrogenated nitrile butadiene rubber)
Number 10 Danco

The Danco#10 is even slightly larger than the dimensions listed but it still works well. It seems that it was the closest o-ring I can find at a hardware store and I wasn't about to order a 100pc o-ring set to find that "perfect" one. LOL

#9 niko_gpsy

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Posted 16 June 2012 - 04:43 AM

View PostNitemare, on 16 June 2012 - 12:22 AM, said:

Is removing/placing an o-ring difficult? Seems like it could be depending on the tolerances.
Removing the O-ring is not difficult at all.  It's that dang "C" clip that's a pain but using 2 micro flat head screw drivers and a little patience it's not too bad after the first few times.

#10 BoobieM4H

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Posted 16 June 2012 - 11:41 AM

View PostJatodude, on 15 June 2012 - 04:41 PM, said:


The problem is probably part number 191, the piston O-Ring.  It's loosing compression.  You could try to replace it, or send it back to KWA.  It's happened to quite a few people.  The problem is remedied by installing a slightly larger O-Ring for better compression.

These two O-Rings where recommended
35/64" x 23/32" x 3/32" hnbr (hydrogenated nitrile butadiene rubber)
Number 10 Danco

Yup

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#11 Cashman1501

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Posted 16 June 2012 - 03:21 PM

Thanks for all the input guys. Ill be going to pick up that oring tonight.

#12 A2Airsoft

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Posted 06 July 2012 - 07:46 AM

View PostJatodude, on 15 June 2012 - 04:41 PM, said:



The problem is probably part number 191, the piston O-Ring.  It's loosing compression.  You could try to replace it, or send it back to KWA.  It's happened to quite a few people.  The problem is remedied by installing a slightly larger O-Ring for better compression.

These two O-Rings where recommended
35/64" x 23/32" x 3/32" hnbr (hydrogenated nitrile butadiene rubber)
Number 10 Danco
Would you or anybody happen to have any extras of these o-rings? I'm having a hard time finding them and I don't really want to spend $40 on a whole kit just for one. Lol
I'll buy if anybody has an extra one

#13 BoobieM4H

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Posted 06 July 2012 - 08:30 AM

View PostA2Airsoft, on 06 July 2012 - 07:46 AM, said:

Would you or anybody happen to have any extras of these o-rings? I'm having a hard time finding them and I don't really want to spend $40 on a whole kit just for one. Lol
I'll buy if anybody has an extra one

Send me a pm..I can get you the kit for $20 (its always good to have extra orings) :)

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#14 A2Airsoft

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Posted 06 July 2012 - 10:32 AM

True that Boobie! Pm sent. I appreciate it

#15 niko_gpsy

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Posted 06 July 2012 - 02:47 PM

View PostBoobieM4H, on 06 July 2012 - 08:30 AM, said:

Send me a pm..I can get you the kit for $20 (its always good to have extra orings) :)

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Yeah but boobie charges $40 for shipping. :rofl1:

#16 BoobieM4H

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Posted 06 July 2012 - 03:47 PM

View Postniko_gpsy, on 06 July 2012 - 02:47 PM, said:

Yeah but boobie charges $40 for shipping. :rofl1:

Isn't that the going rate? Hey where there's a demand I can supply! Haha

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#17 Jakeedaman21

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Posted 06 July 2012 - 06:05 PM

Lube is your friend.

Edited by Jakeedaman21, 06 August 2012 - 11:20 AM.


#18 BoobieM4H

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Posted 06 July 2012 - 10:05 PM

View PostJakeedaman21, on 06 July 2012 - 06:05 PM, said:

The Danco #10s at Home Depot dont work, avoid them...

The ones I sent will tho!

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#19 azzauzi

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Posted 06 July 2012 - 11:10 PM

View PostJakeedaman21, on 06 July 2012 - 06:05 PM, said:

The Danco #10s at Home Depot dont work, avoid them...

Oh snap.

Care to elaborate? (too snug/poor fit,etc?) Those are the ones i bought...

#20 Jakeedaman21

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Posted 06 July 2012 - 11:20 PM

They were to big for the cylinder. The plastic part of tre bolt couldn't move without a lot of force, and wouldnt cycle properly.




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