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

[Impulse]

Hello everyone! Yes, this is a "wat am best gnu?" thread, but I would love to get some opinions and feedback on the research I have already done into this matter. In essence, my m21 build, while I love it, is really annoying me with a jamming issue that doesn't happen all the time and doesn't appear to have any fix (I've tried about half a dozen different fixes and none have stuck) and whenever it does happen it's not the nicest RIF to take apart to extract the jammed BB, so I am going to be in the market for another HPA "DMR" setup. Why do I put DMR in quotations? Because I'm keeping it 1.1J and making it as consistent as possible so it's basically just going to be a sniper rifle with no MED for use at sites where sight lines are limited, like my local site during the summer and the Gunman Eversley sites during their sniper ban time of year.

So that gets me onto the meat and potatoes of the topic. I'm looking at an SR-25 as the base to build on, as I like the AR15 platform but want to keep it 7.62x51mm since I have plans for a recce rifle type build for my MWS in the future which will be the same concept, but loud, gassy and recoil-y and in 5.56x45mm. This one I want to keep quiet and stealthy and 7.62x51mm. Looking through the SR-25 replicas, it seems I have a few options:

- Cyma

- JG

- A&K

- ARES ?

- Classic Army

- G&P (out of production?)

What I'm looking for are good externals and a solid gearbox shell. Gearbox internals, motor, barrel, hop rubber etc are all getting scooped out anyway so I don't particularly care about that. I think they all have somewhat decent externals, but are there any I should watch out for? I think I like the Cyma the most, just because I've owned Cyma guns before and they've always been amazing and it seems pretty easy to get hold of with extra magazines, but I've heard great things about the A&K, though that seems to be out of stock everywhere and the G&P which seems to be the holy grail of SR-25s I just can't find anywhere. Another point for the Cyma is that if I went with it I could leave it as an AEG until I can get a HPA engine for it (they seem to be out of stock in a lot of places), and just do my accuracy upgrades since the platinum edition looks like it performs pretty decently out of the box and has nothing I'd want to change about the gearbox. Inb4 everyone comes in like "the Cyma one is craptastic, don't get it!"

My concern over internals is mostly down to gearboxes, since some appear to be V2, some V2.5, and the compatibility of HPA engines with said gearboxes. Plus, it looks like I'd have to move out of my comfort zone if I went with one of the (many) V2.5 gearbox ones, since Wolverine don't appear to do an engine for the SR-25 so I'd be looking elsewhere (both of my current HPA setups are Wolverine). What HPA engines are out there that are compatible with a V2.5 gearbox? I've found the Polarstar Kythera, but that's about it and I've heard the purely mechanical HPA engines can be less consistent / noisier than battery operated ones (at least that seems to be true with all the VSR systems (mancraft vs bolt m vs bolt)). I'll be fixing it to semi-auto anyway, so that limitation of the Kythera isn't an issue, but I'd rather get some opinions or user experiences before shelling out on something as expensive as a HPA engine.

TLR

Wat am best SR-25?

Wat am best HPA engine for a V2.5 gearbox?

 

[Lozart]

I'll be following this with interest as I have a hankering for an M110!

 

[Crazy_Crystal]

My concern over internals is mostly down to gearboxes, since some appear to be V2, some V2.5, and the compatibility of HPA engines with said gearboxes. Plus, it looks like I'd have to move out of my comfort zone if I went with one of the (many) V2.5 gearbox ones, since Wolverine don't appear to do an engine for the SR-25 so I'd be looking elsewhere (both of my current HPA setups are Wolverine). What HPA engines are out there that are compatible with a V2.5 gearbox? I've found the Polarstar Kythera, but that's about it and I've heard the purely mechanical HPA engines can be less consistent / noisier than battery operated ones (at least that seems to be true with all the VSR systems (mancraft vs bolt m vs bolt)). I'll be fixing it to semi-auto anyway, so that limitation of the Kythera isn't an issue, but I'd rather get some opinions or user experiences before shelling out on something as expensive as a HPA engine.

I think the V2.5 versions will probably be the better option. Unfortunately some of the V2 gearboxed rifs often have very long nozzles which may make HPA engine compatability an issue (I know the Ares definitely does anyway.)

For me A&K, G&P or classic army are the ones i'd look at.

 

[Davegolf]

I was heavily researched into potentially building up an M110.

I know you’re looking hard at HPA, why not make it AEG based?

Use one of the models @Crazy_Crystal has said and what the V2.5 was meant for!

With helical bevel, the right motor and pre-cocking you can make a very quiet AEG.

No not HPA mouse fart but damn good.

 

[Impulse]

I was heavily researched into potentially building up an M110.

I know you’re looking hard at HPA, why not make it AEG based?

Use one of the models @Crazy_Crystal has said and what the V2.5 was meant for!

With helical bevel, the right motor and pre-cocking you can make a very quiet AEG.

No not HPA mouse fart but damn good.

Unfortunately, mouse fart is what I want. Yes, I go HPA for performance because being able to dictate how much air gets pushed out means I don't have to faff around with cylinder-to-barrel ratio, but the main draw to HPA for me is the mouse fart quietness and it's why the only HPA guns I have are sniper rifles. The high ROF speedyboi HPA builds make me sick  

That said I am considering doing this, at least at first since HPA engines seem few and far between for v2.5 gearboxes (and out of stock everywhere). It won't be perfect, but as you say you can make a pretty quiet AEG, especially if it's only on semi, since full auto is what gives away your position far more than the occasional shot on semi.

I think the V2.5 versions will probably be the better option. Unfortunately some of the V2 gearboxed rifs often have very long nozzles which may make HPA engine compatability an issue (I know the Ares definitely does anyway.)

For me A&K, G&P or classic army are the ones i'd look at.

Yeah, this is what I thought too. Unless you get custom parts, the weird nozzle causes issues on the V2 style SR-25s if you drop in a HPA engine for a V2 gearbox. Fortunately, I wasn't a huge fan of the two V2 SR-25s on the list (Ares and G&G).

Whereas the A&K, G&P, Classic Army and Cyma ones all seem to be clones of the same design, which I -think- was the G&P originally.

 

[Davegolf]

You won’t really need to mess with the volume ratio as it’s about perfect for 0.36-0.43 standard, just tune the ammo to it.

What wasn’t mentioned and I think makes for a very cheap build is the Cyma SR25, the innards are plenty strong for 450fps, so you could spend out on a nice brushless motor if you wanted minimum noise and maximum battery life and semi spam cool running.

If not then my ol favourite ASG 22000.

Otherwise for me it’d be; Mosfet with Cycle detection and pre cocking,

Lonex helical bevel/pinion, sorbo only on cyl head, spring to suit, 60d MR bucking with Super Nub.

The other nice thing about battery powered DMR is being able sling it on your back and carry a really useful subgun when moving around or if you’re compromised.

IMO the P90 is the ultimate for this role!

 

[Impulse]

You won’t really need to mess with the volume ratio as it’s about perfect for 0.36-0.43 standard, just tune the ammo to it.

What wasn’t mentioned and I think makes for a very cheap build is the Cyma SR25, the innards are plenty strong for 450fps, so you could spend out on a nice brushless motor if you wanted minimum noise and maximum battery life and semi spam cool running.

If not then my ol favourite ASG 22000.

Otherwise for me it’d be; Mosfet with Cycle detection and pre cocking,

Lonex helical bevel/pinion, sorbo only on cyl head, spring to suit, 60d MR bucking with Super Nub.

The other nice thing about battery powered DMR is being able sling it on your back and carry a really useful subgun when moving around or if you’re compromised.

IMO the P90 is the ultimate for this role!

 @Davegolf, you are really tempting me as I've seen a brushless motor in action and was impressed (my friend wanted to put one in his support gun but it took it up to silly ROF that would've been banned at our local site) and if the volume ratio is already there then I do like that idea, or at least trying an electric build and seeing how it is and if I like it, because I do dislike my line and tank. For the VSR it isn't as bad because I can get away with a tiny tank in a stock pouch that does me for 300 shots and is quick to pump up so it's not attached to me, but if I can do without the inconvenience I would. I don't see an electric build being too much money on top of the gun itself if I go Cyma as the platinum edition seems to come with a lot of stuff I want anyway, and the hop / barrel upgrades I'd be doing regardless.

I can largely do all the tech work myself, even though I dislike working on gearboxes I can do it, but the questions I would have would be around mosfets and pre-cocking. I know the Cyma has a mosfet in it by default for that microswitch trigger and for detecting when the gearbox locks up, but I'm going to assume it wouldn't do pre-cocking and hope that it can lock the gun to semi electronically. I'm just thinking about it and surely pre-cocking puts more strain on the internals and I'm thinking with a warhead motor installed the cycle time for the gearbox would be minimal? I do value longevity, so if the difference that pre-cocking would make would be negligible for the sound profile then I'd rather take the longer life for my internals (because I hate working on gearboxes ). I'll probably send Patrol Base an email or give them a call on Monday and get them to tell me what the mosfet that comes in the SR-25 can do, but I'll take their words with a pinch of salt after they marketed the Evolution M40 as "VSR compatible"

I don't plan on setting it to DMR power, because my local site is 1.64J with a 30m MED which is a bit pointless in my opinion (inb4 @Rogerborg comes in to tell me I'm wrong ?). The power out of the box is exactly where I'd want it, but with the other upgrades I'd be doing I may need to trim a coil or something, but that's not the end of the world and something I can test and remedy with my chrono and ammo of choice. I do like the idea of running it with a small SMG though and I own both a Cyma mp5k that I can sling (which is lovely considering it was £150) or an electric TM mp7 that fits nicely in a holster and still shoots to 45m, so if I can get along with running both the SR-25 and the mp5k at the same time, I may consider DMR power but we'll cross that bridge when we get there. I also own a bunch of pistols that shoot better than most AEGs, so my secondary game is pretty strong ?

So, at the moment what I'm looking at is:
Cyma SR-25 platinum edition plus a few spare midcaps.

Warhead brushless motor (would I go 31k or 45k? I'm thinking 45k would be more snappy, but is it too much / will my gearbox explode / will it really make any difference outside of milliseconds?)

Lonex helical bevel and pinion

Sorbo for the cylinder head (would I want hard or soft for maximum shush?)

70 degree macaron and omega nub (that's just my preference)

Stainless steel 6.03mm prommy (I know it comes with a 6.03 but I have a 509mm prommy sitting unused in my airsoft bits box)

Deans connectors and some solder

Really, the only pricey thing on there is the brushless motor at £170. Can try that for a spell and then decide later on if I want to HPA it, as I now know that on the HPA side it would just be a V2 engine with a different nozzle after chatting with the guys at High Pressure Airsoft about it. Who knows, might just keep it electric. Who knows, might even DMR it! Stranger things have happened (rarely though, these claims are pretty outlandish for me )

 

[Davegolf]

I think youre there, the MP7 or MP5 are perfect.

There are more experienced Warheads out there, i would educated guess say 31k is plenty fast enough with the 18:1

TBH that combo would be so fast precocking is almost nullified, and as you asy reduced strees for sure.

 

[Impulse]

Ok, so I got the Cyma SR-25 and it arrived today. Biggest annoyance was that the suppressor didn't come with any foam in it and it was loud. The gearbox noise is fine as that'll go away once I shove in some helical gears and trade out for a brushless motor, but the muzzle sound was a very noticeable pop without foam in the suppressor. Fortunately I had a crappy 5KU KAC style QD suppressor lying about that was on my MWS, but wasn't tight enough so the recoil caused shots to clip the end when it rattled around. Stripped out all the foam baffles from that and stuffed them into the SR-25's suppressor and it has already made such a difference.

Out of the box it's only chronoing at 0.84J on a .3, though the consistency would make you think it's a HPA gun as every shot was 0.84J, there was almost 0 variance in each shot! Going to tinker around, as I have a Guarder sp100 lying about, but I will probably also buy an sp110, 120, 130 and 140 to toy around between getting 1.1J and 1.6J and see which I prefer. Waiting on a few parts to arrive still, but considering it's already fairly quiet by AEG standards, I'm optimistic about this build.

 

[Sneaky]

Ok, so I got the Cyma SR-25 and it arrived today. Biggest annoyance was that the suppressor didn't come with any foam in it and it was loud. The gearbox noise is fine as that'll go away once I shove in some helical gears and trade out for a brushless motor, but the muzzle sound was a very noticeable pop without foam in the suppressor. 

I have had a selection of different SR25’s and the CYMA one is the best I have had.  Silly the suppressor does not come with foam, but that is easily rectified.  I did a whole load of changes, but stuck with the same gear set. Having the spring change system is great to have.  Mine is very quite, but would like to know how much changing the gears will have an effect on sound.  Any gearbox if shimmed well can be very quite. Most of the sound is from the cylinder head area. Will you be r hopping it, works wonders.

 

[Davegolf]

Noisiest parts of an AEG are the motor itself, the pinion/bevel, the piston hitting the cylinder head.

High quality high torque brushed or brushless motor.

Helical pinion/bevel set

Correct volume so the piston decelerates into the cylinder head, not smash into it, and sorbo to deaden the blow.

A weighty piston also aids this.

 

[Impulse]

I have had a selection of different SR25’s and the CYMA one is the best I have had.  Silly the suppressor does not come with foam, but that is easily rectified.  I did a whole load of changes, but stuck with the same gear set. Having the spring change system is great to have.  Mine is very quite, but would like to know how much changing the gears will have an effect on sound.  Any gearbox if shimmed well can be very quite. Most of the sound is from the cylinder head area. Will you be r hopping it, works wonders.

At first I will be trying an rhop, purely because I have an Umbrella Armory rhop setup that I originally bought for my m14 years ago before I knew m14s were weird. If I don't like it, I'll swap to Maple Leaf 70 degree macaron and omega nub, but we'll see. Umbrella Armory stuff is pricey and I generally don't get stuff from them any more, but it's also generally very high performance. Just need to give the barrel a good clean as it's been sitting in a drawer for years.

My main issue is I don't know how to get to the quick change spring on the full stock version. All the instructions I have show me how to do it for the retractable stock version, but not the full stock

I will want to make use of the quick change spring as I will want to test a variety of different springs and different BB weights to find the optimal setup. Might DMR it purely to get more consistency with heavier weight BBs, as I found that with the 0.84J stock spring it was very consistent with .3s, but not so much with .4s.

Noisiest parts of an AEG are the motor itself, the pinion/bevel, the piston hitting the cylinder head.

High quality high torque brushed or brushless motor.

Helical pinion/bevel set

Correct volume so the piston decelerates into the cylinder head, not smash into it, and sorbo to deaden the blow.

A weighty piston also aids this.

I'll be going with a Warhead brushless motor, though I'm undecided whether I want to top-shelf Ronin or the standard one. Difference of about £50 and I think the standard might just do everything I need anyway. They're very expensive motors, but I think they're probably worth the cost. Also got a helical pinion/bevel set coming in the post from HK, so that'll be good.

Outside of that, I'll be liaising with my friend who is a tech (his favourites are AEGs and he's pretty good at them...) to learn about shimming and get some pointers on the rest of the gearbox stuff to make it silent and efficient. I may be able to get my hands on a set of ZCI helical gears (so all of them are angled like the pinion/bevel I have on the way), so we'll see what works best.

I've already told two of my friends that I will want one of them to help me once the build is completed. Basically I'll go certain distances away (point blank, 5m, 10m, 20m, 30m etc.) and get them to fire it so I can see how close I have to be to hear it so I know what I can get away with in game.

 

[Sneaky]

If the long range of your DMR is good, then they would not know what hit them.

I would be keen to change my motor but I do not think it is worth it, but I will stay open minded.

 

[Hatchet]

My main issue is I don't know how to get to the quick change spring on the full stock version. All the instructions I have show me how to do it for the retractable stock version, but not the full stock

I'll be going with a Warhead brushless motor, though I'm undecided whether I want to top-shelf Ronin or the standard one. Difference of about £50 and I think the standard might just do everything I need anyway. They're very expensive motors, but I think they're probably worth the cost. Also got a helical pinion/bevel set coming in the post from HK, so that'll be good.

Have a look at the review on Reaper's Airsoft Youtube channel. I think they cover it there (they cover pretty much everything else about it).

Also regarding the motors you've got the choice of the BASE which is probably only marginally different from the Black or the Ronin, and £40 cheaper again.

 

[Sneaky]

My main issue is I don't know how to get to the quick change spring on the full stock version. All the instructions I have show me how to do it for the retractable stock version, but not the full stock

You will need a 250mm cross headed screw driver. Remove the rear stock plate.  Turn the gun downwards so you can see into the stock. There will be a black screw within the stock (worth replacing as it is a cheap soft metal - I have replaced mine with a steel screw), towards the rear of the receiver. Remove it and the stock will come off. After that you can undo the spring change block which contains a metal spring guide with bearings. 

I can provide a video on this if needed.

Hope this helps.

View attachment 93768

View attachment 93769

 

[Impulse]

You will need a 250mm cross headed screw driver. Remove the rear stock plate.  Turn the gun downwards so you can see into the stock. There will be a black screw within the stock (worth replacing as it is a cheap soft metal - I have replaced mine with a steel screw), towards the rear of the receiver. Remove it and the stock will come off. After that you can undo the spring change block which contains a metal spring guide with bearings. 

I can provide a video on this if needed.

Hope this helps.

I don't have a long enough screwdriver, though that's easily remedied. I had a feeling it would be something like this, so I'll give it a go at installing the sp100 I have. I think I also have an sp120 lying about somewhere so may try that too. Many thanks for letting me know, I'll have a look around and see if I have any screws that I could replace it with too, as I have a good collection. If not, I'll take the screw down to the local DIY shops and see if they can sort me out.

In terms of the sound, I get that they won't hear me on most of my shots, as even if I'm on 1.1J I'll be taking most of my shots at 30m+ anyway, but it's more for if there are others nearby. Even though it may be a "DMR", the way I will be playing will be wrapping it in its own bush suit while I wear my own bush suit and being a sneaky sniper. Quiet guns are my bread and butter for that, as I like it being difficult for people to triangulate where I am. I'm honestly excited to see how quiet I can make this build, as I've always been a bit of a naysayer for AEGs as stealthy guns and always gone gas or HPA.

Have a look at the review on Reaper's Airsoft Youtube channel. I think they cover it there (they cover pretty much everything else about it).

Also regarding the motors you've got the choice of the BASE which is probably only marginally different from the Black or the Ronin, and £40 cheaper again.

I did consider the base, but the differences posed between the base and standard were worth the extra investment for me, where I don't really see much difference between the standard and the Ronin when I put them side by side. The only differences were:

- Lightened Rotor Assembly.
- Titanium Shaft. 
- Individually hand wound.
- Wired connectors for easy fitting.

Probably not worth the extra £50 for that, honestly. Especially not in a semi-auto locked build.

One question I did have about motors though, am I right in thinking that high RPM is not that important for a semi-locked build? Back when I last looked at motors none of this existed, but I seem to remember the high torque motors tended to have much lower RPM. With these brushless ones am I right in thinking that the super-speed 45k RPM motors would mainly be for full-auto hosepipe builds?

 

[Lozart]

One question I did have about motors though, am I right in thinking that high RPM is not that important for a semi-locked build? Back when I last looked at motors none of this existed, but I seem to remember the high torque motors tended to have much lower RPM. With these brushless ones am I right in thinking that the super-speed 45k RPM motors would mainly be for full-auto hosepipe builds?

100% not important. High torque motors may not have as high an RPM but get there a lot quicker, which IS what you want for a semi-locked build for better trigger response (although short stroking and using a bigger spring does have a similar outcome). Possibly more important will be using a MOSFET that gives you precocking so you don't have all that tedious gearbox cycling before you let fly with the plastic deth!

 

[Davegolf]

Ive just taken the plunge and by my calcs on 18:1 gear set ive gone with a Black Standard speed (20k on 7.4v / 30k on 11.1v)

I intend to run it 7.4 and if i think it needs more speed (read 'response') i can 11.1v it whilst also knowing it wont overspeed and clip a full tooth piston.

 

[Impulse]

Ive just taken the plunge and by my calcs on 18:1 gear set ive gone with a Black Standard speed (20k on 7.4v / 30k on 11.1v)

I intend to run it 7.4 and if i think it needs more speed (read 'response') i can 11.1v it whilst also knowing it wont overspeed and clip a full tooth piston.

You and me both. Went for the standard black motor. Will also test on 7.4v first and then decide if I need 11.1v once I've tested that. It's all coming together...

 

[Impulse]

Ack! First potential hiccup! I both love and hate obsessing over these projects of mine...

So, the Warhead motors come with D-shaped pinions, but all the helical pinions are O-shaped. Curses! If I cannot put an O-shaped pinion on it, I will at least try it without the helical gears and see how it shoots, but if it's still too loud, I'll probably end up putting an ASG Infinity 18k into it with a full helical gear set (either ZCI or Element, as my friend has some). On the plus side, if this is the case, the Warhead won't be wasted as I'll put it in my mp5k along with a 13:1 gear set to terrorise anyone who gets too close or just be a CQB god, though I'd likely need to put in a MOSFET to make sure it's 25rps or less. I feel sorry for anyone who confronts me when running both the SR-25 and mp5k in tandem...

Messaged Warhead about it and they said:

"You can push fit an o-type pinion on the motor but the ESC and sensor does have to be desoldered and removed before push fitting."

"If you push fit an o-type pinion without desoldering the ESC and sensor you will damage the components."

"Once you have desoldered and removed the ESC and push fit on the pinion you will have to solder it back on again. You will not have to replace the shaft."

Now, I am not the most mechanically adept individual so this terrifies me... ?