AOSC Forum Archive

So I am planning on building a DMR-my first airsoft build/trying of any kind- from my KWA M4. I have loads of questions, so techy people (Dom, Skywalker, Star) please help me here.

Goal: build a DMR- semi auto, maximum range and whatnot.

Spring: what do I need? I honestly have no idea. I have a 120 now. I don't want a full auto PDMR. I want a real DMR. So what kind of spring do I need? Any difference between SP springs and M series springs?

Barrel: this is a big question. Is a tight bore worth it? And is it worth it to run it thru a fake silencer to get a few extra inches of barrel (rather than a stock length M4)? I wanted to use a foam suppressor on the end for noise reduction.
*******if I get a flat hop or R-hop installed, is it stuck with the barrel or can it be moved if I got another barrel?

Noise reduction: obviously a foam filled suppressor, but what about a Sorbo pad on the piston? What's the deal with those? What else can I do to quiet the gun?

Gears: obviously I need new gears. Star mentioned there was something funny with KWAs. Help here?

Motor: planning on a Lonex Orange motor.

Piston: Star said Lonex. But what kind? Polycarbonate? Aluminum? Metal teeth? Half metal teeth? What?

Piston head: same thing. Polycarbonate? Aluminum? Bearings and orings? Help me here.

Air nozzle: can someone help me on this? I really have no idea.

Shims: I don't even really know what they are.....

I will probably think of more shortly after I post this. But if you have anything else to add that I'll need, please tell me. Thanks for the help everyone!

It would be easier for you to call me and let me tell you. 803-609-7681.

Unlike Dom, I really quite hate talking on the phone. I much more enjoy writing it all out, so let's take this bit by bet.

Romba wrote: Spring: what do I need? I honestly have no idea. I have a 120 now. I don't want a full auto PDMR. I want a real DMR. So what kind of spring do I need? Any difference between SP springs and M series springs?

A big one. First off, SP rated springs shoot a little hotter than M rated springs. A general rule of thumb, M stands for meters per second with .20g bbs. So an M100 is 100 Meters per second, or mps, M120=120mps, etc. SP springs are said to be chronoed with a .25g bb rather than a .20g bb. Regardless of if that is true or not, they do generally chrono a step higher than normal. Generally, an SP110 is about equal to an M120. So, you're going to be looking for something along the lines of an SP160, SP170, or M170, M180, or M190 for top of the line fps. Beware that heavy springs are less consistent than normal springs, and often shoot much hotter than their rating. The Guarder SP170, for example, is one of the hottest springs on the market, and has the potential to put you over the fps limit. Just something to keep in mind.

Romba wrote: Barrel: this is a big question. Is a tight bore worth it? And is it worth it to run it thru a fake silencer to get a few extra inches of barrel (rather than a stock length M4)? I wanted to use a foam suppressor on the end for noise reduction.
*******if I get a flat hop or R-hop installed, is it stuck with the barrel or can it be moved if I got another barrel?

Ideally, you want something no smaller than 6.03mm in diameter, and something 455-509mm in length. Longer is useless, shorter doesn't have the space required for the bb to stabilize in the barrel. The larger the bore, the more accurate your shots will be. A steel barrel will last longer, and be stronger than a brass barrel. A barrel extension is suggested. Flat hops are generally not barrel specific except in extreme cases, but r-hops are. However, I highly suggest an ER-hop for a DMR.

Romba wrote: Noise reduction: obviously a foam filled suppressor, but what about a Sorbo pad on the piston? What's the deal with those? What else can I do to quiet the gun?

A well shimmed gun is very quiet. Sorbo makes a world of difference. Foam filled absorbs the extra air around the bb. A fast moving gear train is quieter than a slower gear train. Covering up holes in the gearbox, making it almost air tight helps as well.

Romba wrote: Gears: obviously I need new gears. Star mentioned there was something funny with KWAs. Help here?

KWA's gear axles are off spec form the TM standard. Using cheap high speed gears is not suggestible. At your required fps, the stock gears can't dream of holding to a spring like that. Because of these strange restrictions, a torque gear set would be advisable. The only exception would be if you have the $120 to shell out for a Siegetek gear set.

Romba wrote: Motor: planning on a Lonex Orange motor.

Excellent choice.

Romba wrote: Piston: Star said Lonex. But what kind? Polycarbonate? Aluminum? Metal teeth? Half metal teeth? What?

Lonex only makes two pistons; normal, and hard. Both full tooth pistons with 10 metal teeth. If you get a torque ratio gear set, you will most likely be required to use a half tooth piston. That opens up the doors a bit wider. I've had good success with Element half tooth pistons, and limited success with SHS half tooth pistons. You'll want to steer away from full metal pistons and polycarb pistons. They are too heavy, and too weak for what you need. Nylon pistons with steel teeth gear racks are ideal.

Romba wrote: Piston head: same thing. Polycarbonate? Aluminum? Bearings and orings? Help me here.

A bit more open, not as picky given that you have sorbo on the back of the cylinder head. You only need 1 o-ring, 2 orings are expensive/complicated advertising gimmicks and do nothing for your air seal or performance. It's likely you'll need to remove the bearings form the piston head to allow the spring enough room to fully compress. I like Lonex, Prometheus, Core, SHS, Element, and Modify piston heads. It's one of those things that's got lots of options as it's a simple part.

Romba wrote: Air nozzle: can someone help me on this? I really have no idea.

Any air nozzle should work in the gun. See the list above for piston heads, and add Guarder to the list for air nozzles. Aluminum or polycarb, doesn't really matter, as long as it has an o-ring, you are good to go. No need to break the bank on a $15 Prometheus air nozzle when a $5 Dream Army nozzle will work.

Romba wrote: Shims: I don't even really know what they are.....

They are small metal disks that sit on the axles of the gears. They help to take up the slack in between the gears and sides of the bushings, and also help to adjust the position of the gears so they sit together better. I've got a written guide that I believe I've got a link to in my sig. Dom has a good video if that's your learning style. Both will teach you the basics of shimming very well. Shims can be just about any brand you want. I'd stay away from Systema though (I'd stay away from Systema period...) they don't have small shims. I like Matrix shims, SHS, Prometheus, G&G, basically whatever is cheap and has a large variety of different shim sizes.

Romba wrote: I will probably think of more shortly after I post this. But if you have anything else to add that I'll need, please tell me. Thanks for the help everyone!

Don't try to order everything form one store. It may seem like you'll save money on shipping by spending a little more on a different product, but it's often a lesser quality product, and not worth the money in the long run. You end up cheating yourself. It's better to do it right the first time.

Unlike both of these guys, I'm a dick. And I try not to waste my time doing other people's research unless I'm getting paid. And getting paid well.

Google some for existing M4 DMR builds, there are probably thousand of parts lists.

My general thing is; you get what you pay for. There are some exceptions where brand name things are over priced, but a general rule of thumb is, if you go with something cheap, you're getting something cheap.

Its all just going to come down to what you can find in stock when you have the money to spend. No part is so exceptionally ahead of the competition that its worth delaying your gun build to find one in stock.

Simply for love of airsoft I'll throw a few things your way.

I'd do your first DMR with a M150. As you start to build guns that pull more than that, everything becomes exponentially more work and money.

Don't forget to order your silencer from Japan. I'm pretty sure that even then, they are not advertised as foam filled. I'm sure you can Google what brands make foam filled silencers.

Almost all my DMRs have Deep Fire Titanium (Tooth) pistons in them. Never had a problem.

I've used these motors in DMRs: G&P M170 Devil Jet, Systema Magnum, Systema A-Z, JG Blue, and Bravo Xyclone High Torque. I wouldn't recommend the Bravo for anything over a M150 unless you're using torque gears. If you're using torque gears, almost any high torque motor can pull an m150 (when hooked up to a big lipo)...

One area you forgot to mention is the electrical system. Don't forget a mosfet in these guns. You can get them from Steevo for a little bit of money, or spend 100+ on ones like the Cheetah 2n from Extreme Fire. Star and I both have one of those bad boys, and man are they sweet. Use the largest wire you can squeeze into the gearbox to rewire with (I think I've pulled off 16GA believe it or not. Required a dremmel here and there). Then buy a 11.1v Lipo and run deans.

16ga fits great if you use something with thin, hard insulation instead of the wider silicone.

Maybe it was 14 then. I just remember cutting away parts of my gearbox so that the shell would close.

I quit using 16awg long ago in favor of 18awg silver stranded wire with hard insulation. I have run at least 50k through my SPR with that wire and never had an electrical issue or a noticeable difference in motor speed vs. the 14awg I had in it before installing a MOSFET.

Where does one get this kind of "18 awg silver stranded wire?"

I think I got my last batch from www.bulkwire.com.

Romba wrote:Where does one get this kind of "18 awg silver stranded wire?"

If you PM me your address, I can PM you my addess. You could then mail me a couple of stamps, and I can send it for free. I throw away this stuff at work all the time.

Last screw to get my gearbox out. And we don't have any torx that small... What a pain, KWA.

It's an imperial hex head, usually the smallest one that comes in the pack, iirc.

And I hope you've got a good collection of torx heads for the gearbox shell. It uses T9 I believe, a size up from the normal TM T8. It's rather annoying imo, it does nothing but require more parts to take apart gearboxes, and KWA is the only gearbox who uses those screws.

An imperial hex head is different from an Allen key, right?

Same thing, Hex Head = Allen Key. They are both 6 sided tools, imperial means inches, feet, miles, vs metric, where everything is meters. You said Torx Screw drivers, and those are the star shaped ones.

Ohh. I thought it was a torx. I guess not.