KJW M4

[def3kt]

I've tried contacting both us and tw kjw websites about an upper with no replies. Oh well I guess. If any one has a contact email at the kjw offices that would be great.

[t_hum]

KJW will only export plastic uppers. But so far nobody besides KJW is selling them. Im trying to carry spare parts but its proving challenging to get a hold of them.

[elanaiba]

Only export to the US or to "any country"?

[t_hum]

I don't know. Anyone from the EU try yet?

[slipknot1971]

Here is an image what the mod looks like, not really much to say past what I've already said, it works, it's consistent, and it's simple. I'll give more info while I put more rounds through it. I do think one of the more important things is to make sure you keep your hop-up clean, I washed my hop-up rubber in hot soapy water, then rinsed it with hot soapy water, then an alcohol rinse, then cold soapy water, then cold water, then alcohol, then let it air dry, it looks brand new and there is a marked improvement that also helped with my results today, and I think the TDC mod combined with a clean hop-up produces an amazing hop-up.

 

T_Hum as for adjustment, It's not to big of a deal to use what it's currently threaded for, whoever is using it just needs to realize that cranking down on the thing is not going to do what you want it to do, it's very fine adjustments.

 

 

Oh and here is the range I was shooting via google earth

 

and my weapon

 

 

Currently I have these parts in it

 

BC extension

piston cup

x nozzle velocity reducer

6.03 M4 length tight bore

 

I do think that a free floating barrel and rail do help with consistency as I think pressure on the barrel with throw things off internally.

 

 

Hello frog...look...i'm unbelievable astonished with the picture of the range you achieved...i was analizing it and i was like WOW!...that's really FAR!...looking at the image...i noticed that the scale says 70 meters...and if you put that scale on your shoot line..that's a 140 meters...please tell me if i'm wrong, because i talked to a couple of members of my team here in Panama about this mod, and we already contacted T_hum for quotes about the upper receiver job for 5 guns.

 

thanks in advance for your reply....jorge.

[frogfish]

actually the scale says 35m its about a 70m shot or 239ft now this is maximum range (where my BBs were landing) and your results may vary.

Edited March 31, 2011 by frogfish

[slipknot1971]

actually the scale says 35m its about a 70m shot or 239ft now this is maximum range (where my BBs were landing) and your results may vary.

 

Thanks for the help...it's just that i tought that the scale was 35 meters on the middle of it and not the whole scale...thanks!!! anyways it's a superb range!

 

J.

[frogfish]

No problem, yeah the Google Earth scale bars are set up wonky, I only know because it's the same way as the standard scale bars in arcGIS, if it was shooting 140m (460ft) I think everyone would be dropping whatever it is they are using and buying KJW M4s to mod. Still the range is good, however, I was getting this same kinda range with the stock rubber and .2g BBs, but what is really nice is that now my shots are much more consistant and I'm able to use my hop-up with any BB weight unlike previously where I was not able to get proper hop on .28g BBs. I would try cleaning your hop-up, make sure your shrink wrap mod is set nicely (maybe add a drop of cyanoacrylate to the end to keep it in place), then see what you can do, if you can't get your hop setup the way you want or it's not consistent enough I'd send it in to T_Hum.

 

As for cleaning your hop-up this was my method that worked well, I kinda messed up in my previous post but can't edit now

 

1. Rinse thoroughly in hot soapy water (as hot as your tap water can get)

2. Rinse in clean hot water

3. Rinse with alcohol

4. Rinse thoroughly in cold soapy water

5. Rinse in clean cold water

6. Rinse thoroughly with alcohol

7. Let air dry

 

This produced a pristine hop-up rubber and took about 5 mins to rinse, about an hour to air dry.

 

I don't know 100% if this mod will produce the results you are looking for, I still think I need to test this more, and we all need to test it on more replicas. My initial results are great for what I wanted (to shoot a .28g BB flat for 200ft or 61m) that my stock hop-up would not achieve. I just want to make sure you know FOR SURE you want to do the mod before you go through the hassel of sending it up to the states.

Edited March 31, 2011 by frogfish

[slipknot1971]

thanks man!!!...really appreciate it!...and i think that's the same results we all in my team are trying to achieve..thanks again!

 

j.

[kaiba]

Jorge si hablas verga aki jeje,

 

T_hum, thanks for all your assistance and development with kjw. I will mod the hop up in my country today.

[slipknot1971]

Jorge si hablas verga aki jeje,

 

T_hum, thanks for all your assistance and development with kjw. I will mod the hop up in my country today.

 

JODETE MARICA!...HAHAHAHA....Y QUEDASTE ARRASTRANDOTE....

[kaiba]

JODETE MARICA!...HAHAHAHA....Y QUEDASTE ARRASTRANDOTE....

 

Pato, el tornero se panikio x q pensaba q eran de m4 reales, tuve q enseñarle unas mp5, si me mandas el receiver hoy mañana a medio dia salen

[t_hum]

After thinking for a while about how sensitive the TDC adjustments are I did some quick math which led me to a possible conclusion as to why some people have hop issues with the stock KJW and others do not.

 

In engineering there is something we call tolerance stack. When each part is made it has a dimensional tolerance assigned to it. For instance, when a pen is made the tube must fall within a certain length range to be qualified as a usable part. It may be +/- .100" for example. Suppose you took 100 pens that fell within that range and put them end to end and then measured the overall length. If all the measurements were on the small end of the range the length could add up to .100" X 100 too short. A total of 10" too short. Normally there is an average and the overall tolerance deviation is smaller than what Ive illustrated here.

 

What could be happening with the hop parts is tolerance stack. The castings of the upper receiver could be too small or large. Same with the hop wheel, spacer, arm, mounting locations, etc. Some hop units could exhibit significantly less ability to apply hop than others if this phenomenon were pronounced enough.

 

I came to this conclusion by figuring that when Frogfish applies 1/16 of a turn (22.5 degrees) he was getting visibly different resutls. On a 6-32 fastener that means 22.5 degrees of rotation adds up to .0019" vertical travel. That travel is transfered through the arm in an arc meaning that .002 inches affects the amount of hop applied by maybe 2-3 times that much.

 

So if the tolerance stack was lets say .006" out of whack on the hop adjusting parts it could mean we are applying .012 to .018" less hop. That is a significant amount.

 

The only way to prove this theory would be to measure a LOT of receivers and compare parts which probably isnt effective. But if the TDC mods continue to provide positive results I would be willing to be bet my tolerance stack assumptions are correct.

 

Thoughts?

Edited March 31, 2011 by t_hum

[alex chang]

After thinking for a while about how sensitive the TDC adjustments are I did some quick math which led me to a possible conclusion as to why some people have hop issues with the stock KJW and others do not.

 

In engineering there is something we call tolerance stack. When each part is made it has a dimensional tolerance assigned to it. For instance, when a pen is made the tube must fall within a certain length range to be qualified as a usable part. It may be +/- .100" for example. Suppose you took 100 pens that fell within that range and put them end to end and then measured the overall length. If all the measurements were on the small end of the range the length could add up to .100" X 100 too short. A total of 10" too short. Normally there is an average and the overall tolerance deviation is smaller than what Ive illustrated here.

 

What could be happening with the hop parts is tolerance stack. The castings of the upper receiver could be too small or large. Same with the hop wheel, spacer, arm, mounting locations, etc. Some hop units could exhibit significantly less ability to apply hop than others if this phenomenon were pronounced enough.

 

I came to this conclusion by figuring that when Frogfish applies 1/16 of a turn (22.5 degrees) he was getting visibly different resutls. On a 6-32 fastener that means 22.5 degrees of rotation adds up to .0019" vertical travel. That travel is transfered through the arm in an arc meaning that .002 inches affects the amount of hop applied by maybe 2-3 times that much.

 

So if the tolerance stack was lets say .006" out of whack on the hop adjusting parts it could mean we are applying .012 to .018" less hop. That is a significant amount.

 

The only way to prove this theory would be to measure a LOT of receivers and compare parts which probably isnt effective. But if the TDC mods continue to provide positive results I would be willing to be bet my tolerance stack assumptions are correct.

 

Thoughts?

 

I'm not sure if this has been covered but installation of the hop up should be tested as well.

 

I purchased the falcon hop up from redwolf and it fit perfect. I'll post up findings when i get to test them at range.

 

When i was installing the outer barrel, i noticed it took a couple tries to have the hop up arm seated right before turning the dial made any difference. If the hop up was engaged in anything other than 0 and i slid the outter barrel assembly in the hop up would not adjust. I assme because the arm is engaged already it gets stuck on either the side of the hop up bump. I'm using the shrink wrap mod and that seems to had fixed all my problems.

 

Your theory also makes sense, but it doesn't explain when other people have tried different hop up units with the same receiver.

 

Does everyone with hop up problems disassemble upper and lower and look down the barrel to make sure that the hop dial actually increased the hop up prior to a complete assembly?

[t_hum]

I think it actually might explain it. Im referring mostly to the hop parts inside the receiver and how they interact with each other. In could be one part or a combo of parts that causes an excessive tolerance stack. Its obviously hard to pinpoint which part is the culprit without extensive testing but things like moisture levels in the air on the day parts are casted/molded can have large effects on both shrinkage rate and durability. One bad batch of parts tolerance wise could have serious performance impacts.

 

I dont know how KJW or TK control their mfg processes but in many parts of Asia factories are open to the outside and are thus very subject to weather and humidity. Ive seen entire batches of consumer products scrapped from excessive warping caused by moisture.

[frogfish]

T_Hum I was curious about their tolerances because it seems from my hop up system that without the shrink wrap on the arm it wouldn't even engage enough to hop a .2g BB, there is no way TK or KJW would release a product with that kind of a problem unless the didn't design it to have that issue, and it would fit with the claim that some have issues that the shrink wrap will solve, others the wrap dosen't solve and some are perfect OOTB.

 

I also think the step hop dial is an extremely flawed idea, especially with such a limited number of steps, and I don't like the way the arm engages the rubber as it seems to move both forwards and backwards as well as up and down based on it's position. Really what we need is a grub screw to engage directly on the nub of the rubber, much like how a sun project adjustable hop-up functions, I was trying to find pictures but it seems the people I know who still have SPs are either forgetting to get them to me, or not responding to my messages, and my images are MIA.

Edited April 1, 2011 by frogfish

[t_hum]

Direct contact with the nub is no doubt more consistent but the problem with that application on this setup is just a geometry one. I think the nub sits considerably too far forward for the screw to be located beyond where we have it currently. And Im not sure there is enough material anywhere else, anyways.

 

The step hop wheel is fine on paper I guess but in practical use it lacks enough adjustability given the variety of weights and power sources players are using. Infinite hop variability should really be standard here just as it is in many guns. I think the KJ-02 with its knob driven screw design is proof that even KJW realizes that. Its a shame TK veered so far off course on this hop design as nearly everything else is spot on.

 

In the end though Im not sure we can complain too much. This seems to work. Just a shame its not more of a DIY mod. Drilling through the gas tube area gets sketchy with small diameter drills as the surface on the inside of the tube recess is curved. We hit the center of the receiver to .001" and our taps are custom ground on our surface grinder to get the depth of thread we have to go. And gripping the receiver is such a hassle. The first one of these I did I had to use a rather small clamp on the small mill and I was sweating it the whole time. The new clamps make the setup a breeze.

[frogfish]

Direct contact with the nub is no doubt more consistent but the problem with that application on this setup is just a geometry one. I think the nub sits considerably too far forward for the screw to be located beyond where we have it currently. And Im not sure there is enough material anywhere else, anyways.

 

 

Yeah that was more a "perfect situation" type of comment, there is no way we can get the screw that far forward easily.

 

 

I think this will work for the time being, as the pressure applied by the spring and the arm seem to keep things pretty consistant. I really like this platform and now the only thing I hate about it is having to use a unique tool to load the damn mags, I wish I could just use speed loaders.

 

Just out of curiosity is there a way you could design an adapter or something to replace the current feed lips of the thermold mags. I haven't disassembled a mag so I'm not quite sure how the feed lips sit. I'd like to buy you mags when they come out but I can't justify buying a whole new batch of mags in one fel swoop on my current income.

Edited April 1, 2011 by frogfish

[t_hum]

The existing design is pretty busy and complex up top. New feed lips isnt an option.

[Kai_Wolf]

Please let us know how the Falcon hop up rubber works Alex.

[GI Tye]

Two questions:

 

1. Does the front reciever pin remove like the rear pin? Does it have a detent?

 

2. What specifics do I need to look for in a quad-rail forgrip/handguard upgrade purchase? I am looking for a continuous flat top, free floating rail system. Any suggestions on brand or tips on which ones swap right on with little effort?

 

Thanks for the help!

Edited April 1, 2011 by GI Tye

[frogfish]

Yes the front pin removes like the rear, I am unsure about the detent pin, mine does not have one but I bought second hand.

 

Rails, anything that fits a TM spec D ring or is threaded for a TM receiver. My Troy TRX Extreme rails were straight drop on.

[t_hum]

Front takedown pin should have a detent.

[def3kt]

Yeah I bought mine used and the seller didn't tell me about the less than perfect condition it was in. Buyer beware.

[slipknot1971]

Hello friends, well, mayor failiure on my KJW on sunday...broken rear takedown pin....don't ask me why happened since i don't know...it never fell, it was never rough handled, it just happened... anybody here have a test on the NON METAL uppers ????

 

Thanks...