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anybody else shooting 350-360fps?!


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#1 jonsun81

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Posted 17 February 2013 - 06:50 PM

Probably put about 4-5,000 rounds through it and recently acquired a chrono that has me shooting 350 with .2s.  My range and accuracy is admirable, and full auto produces no droppers.

Mods I've done

-Shortened barrel to 273mm
-Changed bucking to guarder
-Replaced oring with danco #10, hbfr ones were too thin.  Did nozzle compression test and it won't budge.

Chronoed at local field and fps was the same, 310 with .3 bbs

Any suggestions?

#2 akiraspeedstar

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Posted 17 February 2013 - 06:55 PM

What are you trying to do? Increase the FPS? Shave the rear of the rocket valve or put a tight bore, the TB will give you a 40 or so FPS boost.

#3 jonsun81

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Posted 17 February 2013 - 07:02 PM

Thought stock it should be hitting around 400fps?

#4 crazyfox

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Posted 17 February 2013 - 07:18 PM

I'm curious, what is the "nozzle compression test" also if you shortened the barrel that can decrease fps a bit.

#5 jonsun81

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Posted 17 February 2013 - 07:28 PM

Boobie showed it to me and its where you plug one finger by the bottom valve hole and another on the hole that faces the barrel.  When plugged, the nozzle  will bounce back when trying to push it into the bolt.  

I thought so too, but other people who have shortened the barrel are still shooting around 400.  Dobeys chrono test with the same barrel length was shooting 380+

#6 akiraspeedstar

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Posted 17 February 2013 - 08:31 PM

You also have to remember that environmental factors can affect FPS as well. Though my gun with a stock cut barrel and a Guarder bucking was shooting about 365fps before I cut the valve spring and get a nice 348-354 spread.

#7 General Pickle

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Posted 17 February 2013 - 10:21 PM

I was playing in 50 degree weather yesterday, shot 350 with .30's, all stock LM4 PTS on propane. Dunno man, my guess would be your barrel is causing the problem, as gas guns get a lot of extra power from longer barrels due to 'power creep'.

#8 jonsun81

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Posted 17 February 2013 - 10:59 PM

Okay, looks like its fine.  I'm in that 350-360 range and seems it is the shorter barrel if akiras fps went down too.  Glad it's not something more serious, thanks everybody for your input.

#9 Chuck S

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Posted 18 February 2013 - 04:29 AM

A shorter barrel affects gas and cartridge guns in a similar fashion.  Both use a fixed quantity of expanding gas and short barrels have a lower muzzle velocity because there's less time to accelerate the projectile while the gas is still expanding in the barrel behind the projectile.  Muzzle flash in a cartridge gun is visible wasted propellent and some of it from a short barrel is impressive.  We just can't see the wasted propellent in our gas guns.

My 14.5" barrel LM4 shoots 420fps with 0.20gm BBs at room temperature and I'd expect a MV drop similar to yours with a shorter barrel.

This gun "likes" 0.32gm BBs which it propels at 345fps (1.8j) with the standard bolt and 391fps (2.3j) with the high power bolt which uses more gas and which may bring your shorty up to standard barrel length velocity.

-- Chuck

Edited by Chuck S, 18 February 2013 - 04:30 AM.


#10 Icurblud

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Posted 14 April 2013 - 03:54 PM

My stock lm4 chrono's 350-360.  I use it at my local CQB field and there limit is 350 on .2's.  I run .25 and it shoots like 313-320

#11 muffinman1604

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Posted 20 April 2013 - 08:17 PM

KWA advertises the stock LM4 to be shooting at 360-380 FPS. Your FPS can vary based on the temperature. Also since you shortened your barrel that could have caused you to lose a small amount of FPS too.

#12 Migwl300

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Posted 06 May 2013 - 05:10 AM

If I install the KWA low power mp7 valve (same thing as the danger werx valve just made by KWA) and the KWA 6.02 TBB on my carbine length LM4, what could I expect the fps to be about?

#13 akiraspeedstar

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Posted 06 May 2013 - 06:21 AM

Without modding the valve Id say you're looking at about 320-330fps.

#14 kaihuang

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Posted 06 May 2013 - 10:39 PM

Mine shoots too hot for most indoor places... Sometimes I hate working weekends only :(
380 with .25

#15 Migwl300

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Posted 14 May 2013 - 06:22 PM

View Postakiraspeedstar, on 06 May 2013 - 06:21 AM, said:

Without modding the valve Id say you're looking at about 320-330fps.
even with a tightbore?




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