Building the best SR-25 "DMR"? Gone Wild: Probably-no-longer-HPA Edition

[Davegolf]

Well that’s a load of wank

 

[Impulse]

Emailed them to see if I can get my order cancelled, so fingers crossed. If not, as I said I'll put it aside for my mp5k build as I do not want to be taking a £115ish motor apart and soldering bits and pieces. Plus I'll need a good secondary if I run the SR-25 at DMR powers. and as I was writing this post I got confirmation that it has been cancelled and refunded. I'll think about going with one if I do want to throw money at my mp5k, but honestly I'd rather not as it's not a "main" gun. Hop rubber and nub is enough for me to throw at that, the stock Cyma gearbox internals are perfectly fine for what I use it for.

Pretty sure the ASG Infinity u-18000 (which I believe is 28tpa, which I believe is nice and torque-y) along with a full set of helical gears will do what I need it to better than a regular gear set and a brushless motor, especially if I run it on an 11.1v battery, as it's that gearbox whine I want to get rid of which seems to be the territory of the helical gears; the motor just reduces the time the sound is being made.

Economic damage avoided. Phew.

 

[Lozart]

Pretty sure the ASG Infinity u-18000 (which I believe is 28tpa, which I believe is nice and torque-y) along with a full set of helical gears will do what I need it to better than a regular gear set and a brushless motor, especially if I run it on an 11.1v battery, as it's that gearbox whine I want to get rid of which seems to be the territory of the helical gears; the motor just reduces the time the sound is being made.

That's the exact motor in my MK12! Is nice, I like.

 

[Impulse]

With disaster averted I finally got around to ordering the rest of the items for the build. The first (and hopefully final) iteration I'm going to test is as follows:

Cyma platinum SR-25

To test power between Guarder sp100, sp120 and sp130. I wanted an sp110 and sp140 as well, but they're out of stock most places.

ASG Infinity U-18000 motor

ZCI or Element helical gear set

Lonex helical bevel and pinion gears

Hard (I believe it's 70D) sorbo pad. I also have a soft one (40D), but from what I've read around, hard will be more useful for the powers I'm going for and the difference in sound is negligible.

Enough shims to make sure I can shim the gearbox perfectly

Pro Win rotary hop unit

Prometheus 509mm 6.03 tightbore with Umbrella Armory r-hop patch and custom hop arm. If I don't like how this performs, I have a Maple Leaf 70 degree macaron and omega nub

For BB weight I will be going anywhere between .32s and .4s, depending on the power and what is most consistent and efficient (cylinder to barrel and all that magic), and I will be testing it on both 7.4v and 11.1v batteries as I now have both. I'm hoping I won't have to tinker around with this build too much beyond the springs and the hop up setup because I don't like working on gearboxes; the spring is quick change and I honestly forgot how easy it was to access the barrel and hop assembly in V2 style AEGs. It's even easier than on my GBB pistols!

For power, the goals are going to be consistency and as near to the limits as possible. I will mainly be testing between 1.14J and 1.64J, as one is for no MED and the other is my local site's DMR power limit, though in time I will want to test for 1.48J and 1.88J as well for if I go travelling to other sites with other rules. Pretty sure 1.48J isn't worth considering, but I'll give it a fair shot. 1.48J and 1.64J didn't impress me when I tested on my HPA setup, so I'm waiting for the SR-25 to show me something that will make me consider 1.64J at least and £10 for an extra spring isn't too much of an investment to try it out (1.88J is worth it for DMRs in my opinion but my local site refuses to budge from 1.64J)

 

[Davegolf]

I’ve got a new spare Lonex bevel/pinion kit if your in need.

 

[Impulse]

I’ve got a new spare Lonex bevel/pinion kit if your in need.

Appreciate it, but I've got one coming in from HK. They were out of stock basically everywhere!

 

[ak2m4]

To test power between Guarder sp100, sp120 and sp130. I wanted an sp110 and sp140 as well, but they're out of stock most places.

Message me and I'll sort you out with some GPA springs if you want

 

[Impulse]

Ok, so it's been a week and I've got some updates!

Firstly, thanks to @ak2m4 and his wonderful shop, I am ready to test at all power levels that I might require. I also bought a set of ZCI 18:1 SR-25 gears as I realised that the helical gears I was going to install may not interface properly with the helical bevel/pinion (which is more important) as the teeth on the bevel gear that interacts with the other gear (not the pinion, they're all swirly) are straight, to interact with a normal gear set. Also SR-25 gears are weird because of the longer piston with more teeth, so while you can use regular 18:1 gears, they won't make use of the longer gearbox and therefore have less air to push through the barrel, which affects the cylinder to barrel ratio and defeats the point of using a v2.5 gearbox over a standard v2, and I definitely want to be using the strength of the v2.5 gearbox for this semi-auto sniper build (whether 1.14J, 1.64J or 1.88J). The stock gears are 13:1, which I gather are better for speedyboi full auto builds, so I wanted to swap them out for 18:1 gears for a bit more of a torque-y setup, so I picked them up alongside some extra springs.

View attachment 94165

Secondly, I tried to install all the things myself. I've done custom builds on all of my gas, spring and HPA guns, so surely I could do an AEG build no problem, right?

Right...?

I was wrong. Tried doing it and I screwed a few things up, plus I couldn't remove the pinion from the motor to replace it with the Lonex helical one. Firstly, I had no idea how to modify the fire selector to disable full-auto, unlike the m14 which was super easy to do so and super reversible if needed. Also, not sure if the gearbox was put back together entirely properly, might've put the fire selector back together backwards (so safe would be auto and auto would be safe) and I couldn't and I couldn't connect up the motor and didn't want to force anything and potentially break stuff, so I put it back together mostly, left the motor outside and bundled it up to give to my local tech, as he specialises in AEGs and loves doing them where for me AEGs are techno-wizardry and I hate them; however I will probably do my AEG m14 myself as funnily enough I find V7 gearboxes easier to work on and I never thought I'd see the day where I'd be saying that. Never let it be said that I didn't give it a good go!

Won't be able to get it to the tech for a bit though. Hopefully won't be too long, but will have to play the waiting game for now. The build now will stand at:

Cyma Platinum SR-25 (with the suppressor filled with foam now)

Pro Win rotary hop unit

Prometheus 6.03 stainless steel tightbore 509mm barrel

Umbrella Armory custom R-hop patch with custom hop arm OR Maple Leaf 70 degree macaron and omega nub

ASG Infinity U-18000 motor

Lonex helical pinion and bevel gear

ZCI 18:1 SR-25 gear set

70 degree 3/16" sorbo pad

To test power (aiming for 1.1J, 1.64J and 1.88J) between GPA m100, m105, m110, m120, m140 and ZCI m130 springs

A bunch of shims to perfectly shim the gearbox

For externals, at the moment I've got:
Strike Systems 3-9x50mm scope (I really like this because it allows me to keep the back up iron sights mounted because I am an immersion nerd)

Outdoor and Tactical 6-9" Harris bipod

Unknown brand KAC-style vertical front grip (though I will eventually replace this with a Magpul AFG2)

Even with all of this in, I think this build has cost me around £500 in total, so compared to some of my other high-performance builds it's fairly cheap, coming in about the same cost as a new TM NGRS, but I think it's going to perform faaaaaaaaar better than one (my HPA VSR, for example which probably cost me around £800)

Still looking forward to getting this done and what I have learned will be really useful for when I do any other AEG builds, which I do plan on doing with my AEG m14 at least and maybe even upgrading my mp5k past the hop rubber and nub which I'll be testing on Sunday (stuck a Maple Leaf macaron and omega nub into an otherwise stock Cyma mp5k to make a devastating little secondary to run alongside this SR-25 if I do set it up as a DMR with an MED).

 

[Impulse]

Time for another update. Had another go at it last night because my pinion tool arrived and I figured that I could do it now that I could swap out the pinion gear on the motor. Removing the pinion and replacing it with the helical pinion was fairly painless, which could be part of the reason for this renewed confidence. But was it false confidence?

View attachment 94534

At first, everything was going okay. Took the SR-25 apart and got to cleaning out the snot that Cyma lube their gearboxes with. Cleaned it all out, followed a guide on how to shim a gearbox properly and eventually got to a point where my gears were turning nice and easy. Things were going well! I then put it all back together, ensuring to put everything back together properly and even making sure the fire selector was put together correctly this time!

View attachment 94535

Then came the monster pain point. The damned motor. No matter what I tried I just couldn't get the motor into the pistol grip. I wrestled with it for literally hours before calling it at almost 1am and going to bed. This morning I tried again and managed to get it in there, but as soon as I test fired...

It cycled. Once. I think the mosfet was like "this battery is low so I'm not working" as the gearbox didn't lock up and it reset just fine after the trigger pull. However, it was LOUD and SLOW. Oh my god was it loud. I must've done something wrong because it shouldn't have been that loud or that slow; the sluggishness could be because of a low battery as the battery I tested was storage charged, but still it was incredibly loud. Louder than my stock AEG m14.

So plan is, as it was before, to give this over to my local tech to sort out. I've had it up to here with this build and unless something dramatically changes I am seriously looking at just getting a Wolverine Inferno and a special SR-25 nozzle. If I do that it won't be for a hot minute because it'll set me back £400 by itself and I don't want to spend that much at the moment.

Parts for my AEG m14 will be arriving today, so I will do that this evening. I am more familiar with the v7 gearbox and I've rebuilt them before, so I'm confident I can do that one properly with a very similar build to this. If it doesn't impress me, the draw to get a Wolverine Inferno for this build will only increase.

?

 

[Lozart]

Helical gears are great when they're spot on. If they're not spot on they're fucking atrocious!

The motor insertion could just be the angle of the pistol grip. When I made my MK12 I used an SPR style grip and it didn't matter what I did with the shimming, the motor was a struggle to seat and sounded like a bag of cats. Swapped the grip to an Ergo style one and it's been SO much better.

 

[Impulse]

Helical gears are great when they're spot on. If they're not spot on they're fucking atrocious!

The motor insertion could just be the angle of the pistol grip. When I made my MK12 I used an SPR style grip and it didn't matter what I did with the shimming, the motor was a struggle to seat and sounded like a bag of cats. Swapped the grip to an Ergo style one and it's been SO much better.

Entirely possible. This was my first real attempt at freestyle shimming (I say that because the Guarder tune up kit for the m14 comes with instructions on how many shims to put where, so that was easy shimming) so I could've done it poorly. I just couldn't believe how noisy it was! Was supposed to quieten the gearbox, not make it assault my ears  

 

[simonp]

Your picture is giving me anxiety as its exactly how i used to work on my gear but i learned a harsh lesson. I highly recommend getting a dish tray or anything else ot allow you to sort collect and manage your parts as your going (and make it less likely for a screw to fall and never be seen again)

I agree with @Lozart on the grip (did the same with my DMR ) not a CYMA shell but alignment with high speed motors will make or break the build

 

[Impulse]

Ok, it wasn't enough. I sorted the AEG m21 build today with helical gears shimmed correctly. Now, I will say that it's amazing how much duller the sound signature is and nobody's going to hear this at 30m, however it's just not enough for a rifle I will likely be setting to 1.1J most of the time and taking closer range engagements. I'll get the AEG SR-25 build done, because I've bought the stuff, however I am now starting the process of saving for a Wolverine Inferno Gen2 plus SR-25 nozzle, though this will not be immediate as it's a pretty pricey piece of kit.

I'm going to HPA it because while I was impressed at how great the quietness is, it's just... not enough. My HPA m21 and VSR builds have spoiled me. I'm just glad I didn't shell out TOO much, though probably about £100 total of parts will end up a wasted purchase ?

 

[simonp]

My DMR doesnt seem any game time for the same reason i would rather stick the tank on my sniper if im playing at range that day as the complete silence is more fun for me

I work under the principle that you have to spend money some times to learn what you prefer (thats my excuse for all the guns in the room anyway), luckily most parts are sellable

 

[Impulse]

I put on my robe and wizard hat to resurrect this from the dead. It's been... a challenging few months for my two AEGs, but the light is at the end of the tunnel!

So I tried doing all the mods and totally buggered the job, plus my m21 wasn't feeding properly. Well, not totally as nothing was broken, but I couldn't get the motor back in and it wasn't shimmed right as it was screeching at me when I did manage to get the motor mostly in. I just don't get AEG gearboxes it turns out, though fortunately there's an absolutely phenomenal tech nearby who also goes to Worthing a bunch (https://www.youtube.com/@adzzzysarmoury is the guy) and he's one of the few people I trust with my gats. So I managed to get it and the m21 to him but he had a very busy end of the year with work, plus I could only really see him at game days, but it was worth the wait. The m21 came back at 1.05J on .32s, nice and snappy and shoots like a laser; ran it at a private game and there were people on the other team wondering what the hell I was using as I was picking them off at range and with pretty precise shots. The SR-25, however... This has had some issues.

Got it back incomplete, which I knew would happen because there was a weird hop setup in it and I forgot to include the other hop arm when I gave it to him. That was fine and I had discussed it with him as I could easily put that in; it was just the gearbox stuff I needed help with. However when I chronoed and took it to the range it was only 0.2J. He sorted that there and then, filing some of the tappet plate away as the nozzle wasn't able to make it all the way forward so the air seal was crap. Sorted, but it was only about 0.6J because the spring was craptastic (good air seal now because it was a very consistent 0.6J. No matter, I took it home, slapped an m120 in it and it was chronoing at 1.17J with no hop on a .32. Perfect.

Took it to the site today and when I put the hop on to float .32s, it was floating them out to the 50m accurately, however when I chronoed it it was now only 0.67J. Far from ideal, so now with the hop set for .32s (though at 0.6J so if I get the power up I'll likely need to take some hop off) I took it home today and started experimenting with springs now that the hop up was set as the m120 was only 0.67J? That was really weird to me.

Turns out mine just doesn't like any spring that isn't a ZCI spring. The GPA and O&T springs I tried just weren't doing well, with the GPA m140 being about 1.2J, which was too strong and also a bit weird for an m140. However, I then put the ZCI m130 I had and the power was 1.3J, which was sort of what I expected out of an m130 in that long gearbox. I also experimented with some of my springs that aren't marked, finding a ZCI m140/150 that was chronoing at 1.84J; if only the DMR rules at my local site were good and made me want to run one, but 1.64J with a 30m MED isn't worth it to me, hence this project is going to 1.14J instead, though it's nice to know I have a spring that'll get me up to the 1.88J mark for if I go to another site or event that allows that. I ended up putting in the ZCI m120 and the power was perfect... Well, mostly. Time will tell as I think I may have to take a bit of hop off which could push it back over the limit, however if that happens I'll just run it on .4s instead to keep it within 1.14J.

View attachment 101075

 

[Leo Greer]

Cool to hear you sorted it! I ran into the same spiral gearset or brushless motor debate on my most recent M4 build, but ended up going brushless and leaving the spiral set for another build. Do you have videos of either of these guns? They both sound like really cool builds, and I would love to compare the sound vs. my brushless M4! 

 

[Davegolf]

Spiral bevel is a must, no high speed/ high load real world bevel gearset has straight teeth!

The sound difference for this one mod is substantial 

 

[Impulse]

Unfortunately I do not have a video of it firing. It's a hard one for me, because I'm used to my gas m700 which makes absolutely zero noise, so everything else sounds really noisy in return. When I ran my m21 at a private game I really felt the difference, as I'd fire it and while it's quiet for an AEG the people on the other team would get a rough idea about where it's firing from due to the noise signature, as opposed to when I use the m700 people have absolutely no idea

In terms of the difference, it's definitely noticeable, but again it's a hard comparison for me because the only two AEGs I have are the SR-25 and the m21. The m21 couldn't take the helical gears as they just wouldn't shim properly in the Cyma gearbox and then the motor also wouldn't fit, so the guy put a different setup in, but the v7 gearbox is naturally very quiet for an AEG as long as it's shimmed properly. The SR-25 does have the helical setup and I've put foam in the suppressor because it comes hollow out of the box, so it's pretty quiet for an AEG, but it still has a sound signature that can be heard. I do, however, have people commenting how quiet my two AEGs are when I take them to the range though

 

[Impulse]

Ok so 2 weeks passed and I had the chance to once again test this build now that I had the power where I needed it and the hop up set, and this will likely be my final post on this journey of building the SR-25 (and boy has it been a journey...). The final parts list is as follows:

• Cyma Platinum cm.098 SR-25 (with foam baffles installed in the suppressor as it comes empty!)
  
• ZCI m120 spring
  
• ASG Infinity u-18000
  
• Lonex helical bevel & pinion gears
  
• ZCI 18:1 SR-25 gears
  
• SHS SR-25 nozzle
  
• Maple Leaf 70 degree macaron hop rubber
  
• Maple Leaf omega nub
  
• Prometheus 6.03 509mm stainless steel tightbore
  
• Outdoor and Tactical Harris style bipod
  
• KAC-style vertical grip
  
• Magpul MS4 sling
  
• Strike Systems 3-9x50mm scope (relatively high scope mounts to accommodate rifle wrap and ability to still mount back-up iron sights)
  
• Run on an 11.1v lipo battery with deans connectors
  
• Wrapped in a Sprinter Custom Ghillie multi-season rifle wrap
  

View attachment 102006

(not getting a picture of it unwrapped because I already wrapped it yesterday and I can't be bothered to remove it!)

This has it outputting a VERY consistent 1.05J, with the occasional shot dropping as low as 1.02J, on a .32; 1.05J means no MED, so I don't have to worry about people getting too close! The range and accuracy is phenomenal, easily hitting a man-sized target at 60m 7/10 times even with the hop rubber not bedded in yet as I haven't put enough rounds through it yet. I'm hoping once the hop rubber is bedded in I'll be able to up that to 9/10 shots, but time will tell on that. However, the big thing is that it is quiet for an AEG. While testing it on the range, I got my friend to fire it as I made my way down the range to see how it sounded. By 30m I could barely hear it, by 40m I couldn't hear it at all. I then asked him to do the same, but on full-auto: by 40m I could barely hear it, and by 50m I couldn't hear it at all. Is it as quiet as a HPA gun? No, but it's amusingly close, so I think I'll be keeping it as an AEG as not having the line and tank is pretty liberating. Honestly, I'm pretty damn pleased with it.

The only parts I will get for it in the future are some sort of trigger replacement MOSFET, like a Perun, when the stock Cyma one eventually burns itself out, and at the same time I'll swap out the stock ported cylinder for a full cylinder, as my tendency to use heavy BBs alongside the long barrel could probably benefit from such a modification, if only slightly. I also have a ZCI m140 or m150 (it's unlabelled) lying about for if I go to an event where I wish to run it as a DMR, though this will only come once I've done the MOSFET replacement since as it stands this SR-25 build is still capable of full-auto. The m140/150 pushes the power up to a cosy 1.84J on a .4, which is just where I'd want it for a DMR, though I haven't tested range and accuracy on that as my local site's DMR rules are just not worth it (1.64J with a 30m MED; I've written borderline essays elsewhere on this forum on why I think that's a waste of time). Going to run it for a few game days and play a bit faster than I normally do with a bolt action as my local site needs some players to start taking the initiative a bit more. Cobra hood and workout rig here I come!

In short, very pleased, would recommend the Cyma SR-25 as the base for a DMR and it will be one of my only AEGs as I really like the performance; the only other AEG I keep is my Cyma m21 build as a backup gun for Vietnam games, but with a full cylinder that thing shoots pretty much just as well as this SR-25 build. Also, HPA isn't always the answer and now I just find the "oh, just HPA it" argument to be a rather amusing one. I still think HPA is a good option, but I also think it is only good for snipers and DMRs (spicy personal opinion, you won't convince me otherwise).

 

[Lozart]

Where did you manage to get the Lonex helical gearset from? They seem to be like the proverbial rocking horse poo!