24 replies to this topic

[Wgusler]

Minor update on the SR-12 DMR build. Completed the work on the gear case halves, piston and cylinder. Gears are shimmed and spin for a long time with no side play at all. Just need the switch board for my Raptor to reassemble.



All the contact areas in the case halves are smoothed and polished . I also trued and sanded the mating surfaces of the case halves .





Cleaned and polished the inside of the cylinder for a better seal and less wear on the o-ring.



Sanded all the contact surfaces on the piston and tappet plate.



Now I just have to wait for parts. I wrote down all the shim mesurments for each gear and then decided to simply etch the total shim mesurment of each gear on the case halves by the bearing for each gear. So when I can't find my notes, I'll still have it.

[niko_gpsy]

Very nice job. Love the polish job on the cylinder.

[jpip]

Nice post.

What kind of mustard do you rub on your cat? Grey Poupon? I'm surprised you dont use Catsup.

[vanevery]

jpip, on 26 April 2012 - 03:19 AM, said:

Nice post.
What kind of mustard do you rub on your cat? Grey Poupon? I'm surprised you dont use Catsup.

What the hell???????
Very funny, though.

Wgusler:
I really like the idea of etching the shim specs into the GB shell halves.
Smart!
Keep us posted as you continue your project.

[superfrog]

This is a reference to the other posting about thus gun.

[kwaispro727]

Wow you sure shined up that cylinder

[jpip]

vanevery, on 26 April 2012 - 07:57 AM, said:

What the hell???????
Very funny, though.

Wgusler:
I really like the idea of etching the shim specs into the GB shell halves.
Smart!
Keep us posted as you continue your project.

Haha. It was a reference to his interests.

[Wgusler]

Update:
Why did nobody tell the noob that SHS 32:1 gears won’t work with a stock KWA piston? I spent a whole Saturday morning prepping the gears, shimmed it until it was smooth as a baby’s butt and the carefully assembled the GB............until it was time to install the piston. CRAP!

I actually started laughing, pulled the SHS's out, threw them in the toolbox and started prepping the KWA gears.

Learned something interesting. The KWA gears are .004 to .006 thicker at the edge. I surmised this was from the gears being hobbed making a raised area around the teeth. I cut the edges back and sanded them until the raised area was gone. My first attempt to shim the KWA's was not going well: When I shimmed enough to make clearance between the gears (.016 to .020), the stack was too tall and was binding when the case halves were tightened down. After trimming the gears, used 1 .007 shim on the bevel, 1 .004 on the spur and .007 on the sector with no shim on top. Less than .002 side to side (measured) and spins forever.

I will post some pictures and chrono numbers when I get time this week.

[niko_gpsy]

32:1 doesn't work with KWA piston?  You may have needed to shave off the second tooth on the piston but it should work.  What was the problem?  It maybe something I am not aware of.

[Wgusler]

SHS says you need to use a half tooth piston as the back gear is as large as the piston engagement gear on the sector. No matter, Just fixed the KWA gears and good to go.

[gcw360]

Some ultra torque gears can be like that.

[Wgusler]

Noob DMR finished product

Heres what we ended up with:
Stock KWA gears shimmed
Azmiuth Piston with stock KWA head and o-ring
Guarder SP 130 spring
Polished KWA cylinder and head
KM head 6.02 TBB
2x bucking and nub
SHS High Tourqe Motor
Extreme fire AB long Mosfet
11.1 V/ 2250/ 30C Lipo
M-Star 6x42 Fixed power scope

498-510 FPS with .2's
23-24 RPM
28 of 30 rounds of .3's in 6" circle at 150 feet ( prone with a bi-pod)

I am quite happy with the gun and don,t  see me changing anything except adding the IR-hop. This thing shoots great up to 150-175 feet and dies off anywhere past that. I hope the R-Hop can get me to 200-250. All and all a fun project and i learned quite a bit. Thanks to all you guys  for your help .

[superfrog]

Something is not right here.  A stock sr12 will shot like this at 200 feet.
How did this shoot with stock barrel?

[niko_gpsy]

superfrog, on 01 June 2012 - 03:12 AM, said:

Something is not right here.  A stock sr12 will shot like this at 200 feet.
How did this shoot with stock barrel?

You have to remember that the stock 2G bucking and nub has an effective FPS limit of about 475fps. He would definitely have to look into either a firefly or RHop setup for longer range.

[superfrog]

Interesting, I forgot about that.  So, in this situation,  high fps actually reduces performance.  If the spring were downgraded to an sp120 range and accuracy would improve due to bucking being able to work properly.  Seems counterproductive, but each to there own.

[niko_gpsy]

superfrog, on 01 June 2012 - 03:54 AM, said:

Interesting, I forgot about that.  So, in this situation,  high fps actually reduces performance.  If the spring were downgraded to an sp120 range and accuracy would improve due to bucking being able to work properly.  Seems counterproductive, but each to there own.

Yes I agree and that is why I do not encourage high fps builds without a proper hop up setup. A firefly buffer rubber alone should increase that limit a bit.

[Wgusler]

The gun will shoot 200 feet, but not accurately. With the stock GB and spring, it was far less accurate and consistent at this same distance.  A stock SR-12 may shoot 200 feet with .3’s, but not a 6” group for 30 rounds. Or at least mine didn’t.  I measured the actual distance we tested at and it was 167 feet. At 250 feet, I can hit the target box ( 18” x 29”)  but the grouping and constancy isn’t there. Adding more hop makes the rounds climb too much. As is, the rounds are straight as a string with no climb at 167.  I will get the r-hop installed and see where we are at.

Might be I define how far it shoots diffrently than others. Lobbing shots by using a bunch of hold over isn't accurate to me. Can I hit a person sized target at 250? Sure. If they are standing in the open and still. Can I hit someone in the head peeking from cover at 250? I doub't it. If the R-Hop can get me grouping at 6" at 200+ I will be thrilled.
  
As far as “in this situation, high fps actually reduces performance” you have to be kidding. Stock with orignal spring and with the m130, same distance, the grouping was 8" to 12".  In this case, it is more accurate and shoots further than it did stock. "Downgrading" to an an SP120 ( m130) would hurt as I have already shown.

   I keep hearing the “FPS doesn’t equal range” repeated over and over and that is not only inaccurate, but an oversimplification of the ballistics ( energy)  involved.   Setting up a gun to fire at the field limits of FPS ( energy) to gain the most range and ability to fire heavy weight bb’s is a logical upgrade to an AEG. My feild has an 500FPS limit (+/-10) for DMR's and that is what my gun is built for.

Edited by Wgusler, 01 June 2012 - 09:49 PM.

[kwaispro727]

FPS = range but only with the right hop-up setup.  Even then there is a limit to how much FPS will help you.

[superfrog]

Ok, but I would like to point out that changing a spring from an sp120 to a sp130 will not make your groupings tighter at 167 feet. The bbs will get there a but faster but nit enough to notice.  Further, what I was referring to if you read was niko comment about the stock bucking becoming less effective at higher fps like yours.  
Also remember we are responding to your post with limited information.  You wrote that is shoots great at 150 - 175 feet and dies off after that.  Now you are saying you can hit a box at 250 ft.  That info makes a difference.  

And fps dies not equal range.  That is an absolute fact.   Here is why.  
In other countries the fps limited are rather low. Top end being about 350 yet some have guns able to hit 250+ accurately.

It is the hop up set up that makes most of the difference.  At my field I was using my stock Sr7 with rhop at 350 fps and out ranging linger and much stronger fps guns.  Fps will help a to an extent but not what you would think.

Another example. My video of rhop was hitting my son at 300 measured feet with Sr10 barrel, but same gun with stock shorter barrel could not reach out as far.  No change in fps but different results.

Point being in a kwa the stick bucking doesn't work properly with guns shooting over 475 fps.  I am sorry if you don't believe this but it is true.

But an rhop will make a difference, but hey what do I know?

[Wgusler]

superfrog, on 02 June 2012 - 01:12 PM, said:

Ok, but I would like to point out that changing a spring from an sp120 to a sp130 will not make your groupings tighter at 167 feet.

Well, something did. Best group before was 8.5 ", best group now is 5.67" Might be the addition of the mosfet or changing the piston?

The bbs will get there a but faster but nit enough to notice.  Further, what I was referring to if you read was niko comment about the stock bucking becoming less effective at higher fps like yours.  
Also remember we are responding to your post with limited information.  You wrote that is shoots great at 150 - 175 feet and dies off after that.  Now you are saying you can hit a box at 250 ft.  That info makes a difference.  

Yea, my bad. When I say "dies off" I am refering to dropping some, curving and the grouping spreading . I can hit the box at 250 by holding over about 75% of the time. Not what I consider usable range.

And fps dies not equal range.  That is an absolute fact.

No, not in fact, a fact. So a 100 FPS gun can reach the same range as a 400 FPS gun? Nope.

How about we say that very high FPS isn't equal to increased range?

  The energy produced vs the mass of the projectile and the friction loss from the barrel, the air and gravity dictate the range. If the energy level is low vs the same mass and friction, it will not have the same range as a higher energy level vs the same mass and friction. However, this isn't a simple 1 to 1 caculation. While the mass and gravity remains constant, the friction loss will increase a small amount at at higher speeds.

As with any fired projectile, there is a point of diminishing returns on FPS. So we can speculate that over 400 to 500 FPS that there will be no mesurable gain in range. Is this a fact? Has anyone taken a 400FPS gun with a properly tuned R-Hop mesured the range and then raised the gun to 550 or 600 FPS, re-tuned the R-Hop and find out if there is any increased range?

  Here is why.  
In other countries the fps limited are rather low. Top end being about 350 yet some have guns able to hit 250+ accurately.

And your gun shoots 400+ and it shoots 300 feet. Will it shoot 300 feet at 350?


It is the hop up set up that makes most of the difference.  At my field I was using my stock Sr7 with rhop at 350 fps and out ranging linger and much stronger fps guns.  Fps will help a to an extent but not what you would think.

I agree.

Another example. My video of rhop was hitting my son at 300 measured feet with Sr10 barrel, but same gun with stock shorter barrel could not reach out as far.  No change in fps but different results.

But without the R-Hop, correct?

I don't want to turn this into a 9 page debate, lets just say that there is a limited return when the FPS reach a higher level. That I agree with.

Point being in a kwa the stick bucking doesn't work properly with guns shooting over 475 fps.  I am sorry if you don't believe this but it is true.

Where did I say that this wasn't the case?  I clearly stated in my post that I was finished with the build except adding the IR-hop.

But an rhop will make a difference, but hey what do I know?

No need to be a smarty pants on my account, I freely admit to being a noob.

Worked on the R-Hop today and have it installed with a cut down m-nub. Got too dark to test it,  but I will start tuning it in the AM.

A side note on the range of my gun in testing: When I removed the barrel to do the hop it was very dirty. Lots of grease and gunk from working on the GB. May be why the range was not what you thought it should be. I cleaned it but that will screw up any comparision of before and after the hop. Oh well, I just want 6" at 200 and I will be thrilled.

Edited by Wgusler, 02 June 2012 - 09:24 PM.