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Need help predicting the FPS.


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#1 Migwl300

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Posted 22 May 2013 - 03:08 PM

I am planning on installing the RA-Tech 6.01 and hop up unit and then install the danger werx flute valve.  right now the gun shoots 350 with .30g bbs.  what do you think it would shoot with these two mods?  I think the valve would bring it to 320 with a .20 and the barrel would bring it up to around 400 with .20s.  am I wrong? any other suggestions for increasing the range and or accuracy with out raising the FPS that much?

#2 thatguyx

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Posted 22 May 2013 - 05:00 PM

your mileage may vary.  The MP7 Dangerwerx valve has been reported to drpo fps between 60-100fps, there is however a newly released Dangerwerx LM4 CQB valve, which supposedly drops 40-60fps.  I have not seen any chrono numbers as of yet though.  The RA-Tech tbb can raise between 40-50fps, less if you cut down the barrel.  It's hard to say what exactly you'll be getting, must account for bb weight/power creep, temperature, compression, Mars position relative to Venus, etc.


:edit it's tough to say really, what weight bb do you plan on using for chrono?  Are you tuning for outdoors/cqb/max fps for plinking?  Most LM4s i've seen shoot in the neighborhood of 380-390fps stock with 0.20g bbs.  Throwing in the Dangerwerx valve (mp7 version) should drop you to around 300-320, putting in the tbb will pick it back up to 340-360 fps all with 0.20g  ~ 1.13-1.7J  Given power creep and moving up to 0.30g bbs, I'd expect you shooting around 300-310fps with 0.3g  ~= 330s with 0.25g.  However, I haven't taken into account how much a ra-tech full length tbb could raise your fps since i've cut mine down.

:edit2  to increase range and accuracy, look into the evoII/ksc hop up kit, introduced by boobiem4h.  You really don't even need to mess with the fps if you're playing outdoors.  However the evo kit may take some tweaking if you don't want to use heavier than 0.30g bbs

Edited by thatguyx, 22 May 2013 - 05:36 PM.


#3 Migwl300

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Posted 23 May 2013 - 05:04 AM

Ok do you think the valve from the kwa mp7 low power bolt will effect the fps the same as the danger werx mp7 valve. It lowered the fps from 400 to 355 with a .20. Then tight bore will raise it is about 400, keeping it legal. Pretty much do I have to buy the danger werx one or can I use the the one from the low power bolt for the mp7? And will they preform the same?

#4 akiraspeedstar

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Posted 23 May 2013 - 05:56 AM

Wow your gun is shooting pretty hot for a stock LM4. Also that's interesting that your MP7 bolt lowered it so little, most people got 80-100+ fps reductions. I myself had it drop from 400 to about 295 or so when I had an mp7.

Anyways with less gas the barrel will have less of an increase in FPS as there will be less pressure and gas expanding. So as mentioned a TBB plus a DW MP7 valve will equal about 340fps with .20g bbs. Shaving the valve or buying the LM4 valve will get you around 350-360. You could also install a stronger rocket valve spring or stretch the OEM one to raise it a little more. Though the DW valve with how much it blocks the nozzle opening you can't really get the fps to high.

A good way to tune your FPS would be to cut the rocket valve spring. This will take some trial and error but you'll be able to get the fps down to where you like it if you take your time.

#5 Migwl300

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Posted 23 May 2013 - 10:05 AM

Ok I'll install the RA Tech TBB and the KWA lower power mp7 valve. I'll report back what happens.

Ok I'll install the RA Tech TBB and the KWA lower power mp7 valve. I'll report back what happens.

#6 Migwl300

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Posted 28 June 2013 - 09:15 PM

Just got the RA-Tech installed and it was chronoed at 390 with a .30.  So that's about 450 with a .2.  I'll report back once I get the low flow valve installed.

#7 Migwl300

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Posted 12 July 2013 - 06:05 PM

Just got my LM4 back with a angel custom low power valve installed.  now it shoots 290-300 with a .25g bb.  i would say that is about 320-330 with a .20g bb.  this is great.  once I buy the parts for another bolt.  I can runn the LM4 indoors and outdoors.  i'm gunna run the current bolt for indoor and build a bolt that shoots 320-330 with a .30g bb.  the conversion chart I use says that with like 400 with a .20.  anyway could not be happier.

Edited by Migwl300, 13 July 2013 - 06:59 AM.


#8 Fox Weik

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Posted 12 July 2013 - 09:07 PM

View PostMigwl300, on 12 July 2013 - 06:05 PM, said:

Just got my LM4 back with a angel custom low power valve installed.  now it shoots 290-300 with a .25g bb.  i would say that is about 320-330 with a .20g bb.  this is great.  once I buy the parts for another bolt.  I can runn the LM4 indoors and outdoors.  i'm gunna run the current bolt for indoor and build a bolt that shoots 320-330 with a .30g bb.  the conversion chart I use says that with like 400 with a .20.  anyway count not be happier.

is that a chart for GBBR's and your barrel length?

#9 Chuck S

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Posted 13 July 2013 - 04:43 AM

I'm guessing your LM4 will chrono under 350fps with 0.20g BBs but unless you have a GBB velocity chart I can't predict much more than that.  Let us know what it shoots.

We had a discussion a couple of months ago that noted that GBB guns react much differently than AEGs to BB mass and barrel lengths.  AEG charts are inaccurate in predicting muzzle velocity with GBBs.  AEGs have a limited supply of propellent based on their cylinders while GBBs react much like cartridge guns as the gas expands until the BB clears the muzzle.  Your predicion of 320fps with 0.20g BB based on 300fps with a 0.25g BB may be low (but probably well under 350fps).

I use the military/LEO "training bolt group" sold by KWA and on a typical day average 391fps with 0.32g BBs and my hopup settings (it'd be faster with the hopup off).  Muzzle energy is 2.28j.  CQB energy level limit is 1.0j which works out to 100mps muzzle velocity with a 0.20 BB.  The 350fps limit of most CQB venues is just over 328fps (100mps) and the BB's velocity drops quickly.  Minimum engagemet ranges assure the BB is under 1.0j at impact.  Standardizing testing with 0.20g BBs allows airsoft venues to avoid a bunch of math.  :)

-- Chuck

#10 Outlaw1995

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Posted 13 July 2013 - 06:44 AM

View PostChuck S, on 13 July 2013 - 04:43 AM, said:

I use the military/LEO "training bolt group" sold by KWA
-- Chuck
Question: how did you get a hold of one? I thought they were only sold to LE or military types... are you one of those?

#11 Migwl300

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Posted 13 July 2013 - 06:57 AM

I was looking at a AEG chart so you might be right, it could shoot 340-350 with a .20.  I will try to get my hands on some .20s because all I have is .25 and .30 bbs.

#12 Chuck S

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Posted 13 July 2013 - 12:54 PM

I am "one of those" but didn't think KWA restricts the sale.

-- Chuck

#13 gcw360

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Posted 13 July 2013 - 02:46 PM

View PostChuck S, on 13 July 2013 - 12:54 PM, said:

I am "one of those" but didn't think KWA restricts the sale.

-- Chuck
Right now, they are promoted and sold to LE typically.  That may change in the not so distant future.  Niko and I each have one and are currently testing them. With .3 KWA BBs, I'm getting between 430-400 from 1st shot through say 10 rounds and depending on the mag I use at just below room temp, about 70 degrees.  Most times It's stable from about 400-410.  The stock bolt yeilds about 330-365ish over a range of shots. Again, depending on the mag use.  Note: Some mags shoot hotter than others.

Oh, and Niko got 477-480 w/.2 at 78 degrees.

I'm liking this bolt!

#14 Chuck S

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Posted 13 July 2013 - 03:59 PM

As noted i'm getting about 390fps with biodegradable Elite Force 0.32 brown BBs.  Using dark color BB eliminates the "tracer effect" of white BBs and forces use of the sights.

My gun is otherwise functionally stock although it has a Magpul stock and railed handguard to mimic my "duty" LWRC M6 carbine.

The velocity helps in my opinon although most of my shooting is against scaled targets (9" silhouettes) mixed with full scale targets out to 50 feet or so.  Used in training courses mainly for demonstration purposes as well.

I've not taken the bolt carrier apart so have no idea what modifications KWA did to get the muzzle velocity up.

-- Chuck

Edited by Chuck S, 13 July 2013 - 03:59 PM.


#15 Migwl300

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Posted 20 July 2013 - 08:41 PM

I fielded my LM4 today and it was good.  I have the brass RAT tension arm and after every about ten shots or so a bb would roll out of the barrel.  the gun was shooting lower than I expected, 270 with a .25.  I think i am going to get the EVOII and maple leaf combo that boobie raves about.  i'll report back once it is installed.




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