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FPS adjustment


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#1 Fox Weik

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Posted 01 February 2014 - 09:45 PM

what do you guys use/recommend for adjusting FPS between outdoors and indoor fields?
Right now i use the RA Tech NPAS but i seem to have nothing but issues with it, i aeem to have an issue with the valve falling out of alignment.

#2 General Pickle

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Posted 01 February 2014 - 10:50 PM

It would seem the best solution for this common problem is to set up two bolt carriers with different valves; switching FPS would be as easy as pushing one pin, swapping bolts, then BOOM everything is good to go. From what I recall a full bolt carrier with valves and all is about $150-200 USD, though maybe the prices have come down since I looked last.

#3 BeachEMT

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Posted 02 February 2014 - 12:56 AM

Supposedly the MA LM4 has a guide in the bottom of the nozzle that may help with that.

#4 Chuck S

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Posted 02 February 2014 - 03:45 AM

I've not noted much success with the LM4 and variable valving.  A complete power bolt carrier group should cost under $100.  What modifications you need to make are probably covered in several threads.  If you're going to the trouble a high power bolt can probably be setup to match the KWA Mil-LE-Training bolt which runs 390fps with 0.32gr BBs in my otherwise stock LM4 and a second low power bolt at under 350fps with 0.20gr.  I'm thinking, though, the the differences will be in the valve and spring in the bolt carrier so a "quick change" setup with a complete second bolt may be overkill.  Certainly convenient and no little C-clips to bounce around your room to disappear forever.  BTW, the dust cover uses the same C-clip if you ever get in a real jam.

One issue with the LM4 or any gas gun is the muzzle velocity is highly dependent on ambient temperature and setting one up at just under the typical CQB limit of 350fps may result in it being over in warmer temperatures.  AEGs, on the other hand are much more consistent.

-- Chuck

#5 Lost

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Posted 03 February 2014 - 07:57 AM

Another way to drop the muzzle velocity is to change the propellent (ie. Use duster gas for indoors and Green Gas/ Propane for Out doors). I remember my LM4 functioning with duster gas when I was shooting it indoors but I did not experiment/test many conditions so I cannot gaurantee that it will work in every condition.

A Link to a previous post with the same idea: http://www.kwausa.co...showtopic=10089

#6 Fox Weik

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Posted 07 February 2014 - 08:15 PM

well i called the pro shop today and was able to order 2 BCGs at my desired FPS so hopefully the BCGs are going to be alot more reliable then my NPAS

#7 Chuck S

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Posted 08 February 2014 - 03:17 AM

Keep us up to date on this although I realize your outdoor use won't start for months with this weather!  :)

-- Chuck




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