Double Eagle M906C (Easy/cheap upgrades) vs M904G (Better barrel and hop unit)

[RostokMcSpoons]

My recent travails with my otherwise beloved Double Eagle have indicated a failing Falcon Fire Control Unit (it's a decent MOSFET with some active braking + burst modes etc)

To combat this I firstly bought a 904G (because it's exactly the same internals) as the Falcon units aren't available as spares.

And then I bought a Falcon unit as one became available!

This has allowed me to fix my DE M906C (yay!  but it's still needing some work, more on that later)

And I have a fully working DE M904G with a better barrel and hop combo installed.

Time to "science the shit out of it" and see which is better!

Now the 906C is not stock.   It has had the super-easy upgrade of the Maple Leaf 50deg Macaron bucking, paired with an Omega nub fitted.  When I tested this on installation, I didn't find much difference, but the guns shoots very accurately and consistently to decent distances.  

The 904G has had a ZCI tight-bore inner barrel and ZCI rotary hop fitted.   Both things are widely recommended on these forums.  A Prometheus hop rubber has also been fitted.

How can we tell which is better?

View attachment 115069

I set them both up with my Visionking 1.25-5x scope, set it at 5x, roughly zeroed and then grouped 20 shots.

View attachment 115070View attachment 115071

(Apologies for mislabelling the 906C target)
 

Pretty much sod-all difference!  If anything the 906C is better, as the 904G had a tendency to throw a couple of real flyers into the mix during zeroing.

A couple of minor observations:

1) The 904G has been well shimmed, sounds pretty good.  The 906C has still got the factory shimming and sounds like an asthmatic ant with some heavy shopping in comparison, though there seems to be no loose movement in the gears.

2) Both are running the stock grey motor (Chaoli? (sp???)).  The 904G runs warm after spamming semi, the 906C still tends towards "frying tonight" even with the new control unit running things.   More backing for the idea it's badly shimmed?

3) The 904G is chrono-ing at 280fps with 0.28s and no hop, which is decent.  The 906C was at a little less (there's always some hop applied, thanks to the nub) 

Perhaps the 906C is too tightly shimmed?  Better too loose than too tight  ... in this context 

I've tried different motor heights, but the better it sounds the faster it heats up. 

Anyway, I think I'm going to swap the 904G gearbox into the 906C and then maybe to do some more 'science' with different combos of barrel and hop unit... but I suspect the difference in their abilities will only show up at much longer ranges than the 15m I've tested at so far.

Edit: I swapped around some shims on the 906C, and put it in the 904G receiver, and vice versa.

The 806C original gearbox now sounds better, and the 904G gearbox in the 906C receiver now sounds worse    Maybe the polymer receiver deadens the sound better than the metal one...?  And maybe the motor height needs some more work - @Speedbird_666 your clever shim I don't think is needed with the 906C, it has a different, noticeably longer, pistol grip.

 

[Leo Greer]

Too loose is indeed better, but in my experience you can have too tight of shimming and still have a good sound. Most of the cycling noise is related to the bevel-pinion junction, and how well the teeth match up.

I believe your results will probably hold true for longer ranges as well, given that the barrel and rubber don’t affect the BB once it leaves their influence. So, the variance you see now should carry over, extrapolating into similar variance at any range.

Have you perchance done stabilization mods on either RIF?

 

[gavinkempsell]

With SFA knowledge about this, can I ask... did you try different batteries while testing? 7.4, 11.1 etc. or even different gas if not elec.

 

[MrTea]

Try using a 60 degree bucking (the yellow one) for 350fps and test again? As Leo Greer suggests, stabilising the inner barrel inside the outer may be required to improve accuracy further. Currently working on this myself but i'm waiting on more parts to arrive.

 

[RostokMcSpoons]

Too loose is indeed better, but in my experience you can have too tight of shimming and still have a good sound. Most of the cycling noise is related to the bevel-pinion junction, and how well the teeth match up.

I believe your results will probably hold true for longer ranges as well, given that the barrel and rubber don’t affect the BB once it leaves their influence. So, the variance you see now should carry over, extrapolating into similar variance at any range.

Have you perchance done stabilization mods on either RIF?

I'm still a noob when it comes to shimming.   So with the 906C gearbox I just swapped the shims around because the sector gear wasn't spinning very easily when it was just the 3 gears inside the shell, and some of the gearbox screws done up.  I moved one of the thin shims from the top to the bottom of the sector gear, and it improved.  I may have moved another from one gear to another, I can't remember for sure.  (I considered it a 'win' anyway!)

Yeah, I'm thinking more in terms of how well it hops rather than deviation from the barrel...  

I've not stabilised the inner barrel - I'll look that up and experiment!

With SFA knowledge about this, can I ask... did you try different batteries while testing? 7.4, 11.1 etc. or even different gas if not elec.

Just a small stick 7.4v.  Once the spring is back, it's all down to the stored potential energy in that rather than anything electrical, so batteries will (well, should) only affect the RoF.

Try using a 60 degree bucking (the yellow one) for 350fps and test again? As Leo Greer suggests, stabilising the inner barrel inside the outer may be required to improve accuracy further. Currently working on this myself but i'm waiting on more parts to arrive.

I've not checked the ZCI barrel / hop, I presume the Prommy rubber is purple, as that's the one usually recommended from them.   I'll check, I may have a spare yellow ML bucking, or it may be installed in the 904G now - one way or another I'll try it.  Good results with ML regardless of whether it was 50 or 60 previously, so happy to stick with 'em!

Does inner barrel stabilisation require parts?  I thought it might just be a bit of electrical tape to center it in the outer barrel!   

 

[MrTea]

Does inner barrel stabilisation require parts?  I thought it might just be a bit of electrical tape to center it in the outer barrel!   

Not really. I've seen guides on the internet of people using PTFE tape to things like scotch tape and just layering it up.

Companies such as Airtech Studios make Inner Barrel Stabilisers but i've bought their stuff and it's super picky with fitment. I tried fitting one (out of curiousity more than anything else) to my Krytac LVOA-C and it wouldn't even fit around the Laylax/Prometheus stainless barrel which is a direct replacement for the stock brass barrel. I'd have to measure the diameter with my calipers before i'd call their stuff a complete bust though. I imagine you could stretch the plastic around the outer barrel if you heated it up enough... ?

I tried fitting their L85A2 stabiliser to my G&G L85A2 and that fit fine (stock barrel)... but it will only fit with the standard flash hider due to it's design. Only way around that is to turn it into a sleeve but then there's no guarantee of it staying in place.

This post might interest you on the Airsoft Sniper forums.
 

 

[RostokMcSpoons]

Thanks chaps, Leo's post on the Airsoft Sniper forum, linked on the previous message, is a good read   

As for stabilisation... I found this page 
I've got PTFE tape, so I can try that tomorrow if I get the time.

I've got one problem away from the accuracy fettling...

When I was rebuilding the 904G, I managed to cross-thread the stock bolt into the spring guide.  Currently they're jammed together (there's a plastic bit of the stock that prevents me from getting a good hold on the spring guide to unjam it all, but I should be able to sort that out tomorrow.)  The issue did bring forward my plan to replace the 'tanker' stock with something like the 906C so I can use a better spare stock on there... so presumably I need to buy a rear sling plate, and a generic M4 AEG stock tube?  Is there anything else? 

 

[Fatboy40]

The issue did bring forward my plan to replace the 'tanker' stock with something like the 906C so I can use a better spare stock on there... so presumably I need to buy a rear sling plate, and a generic M4 AEG stock tube?  Is there anything else? 

You'll probably find this a lot harder than you expect as the polymer bodied M904's use a funky adapter on the rear of the receiver to mount the buffer tube, with plastic lugs either side.

Look at photo's comparing the 904G and E, note how the G has longer plastic "runners" on the adapter. To swap to a buffer tube on the G you'll either need to find the part from DE (near zero chance of that) or find a boneyard E being broken for spares (a 3D print of what you need probably wouldn't be anywhere near strong enough).

 

[Lozart]

As for stabilisation... I found this page 
I've got PTFE tape, so I can try that tomorrow if I get the time.

Honestly - don't waste your time. Unless your inner barrel is flapping about like a dick in a shirtsleeve, wrapping anything around it to stabilise it is a bit pointless unless you're looking to make it into a DMR in which case there's plenty of other things to try first.

 

[Rogerborg]

Counterpoint: since shimming the barrel is about the cheapest and quickest thing that it's possible to do, why not?

View attachment 115227

 

[RostokMcSpoons]

I'll do the shimming of the inner barrel and do a test shoot, see it it makes any difference...

All in the name of science!

The stock is giving me the right arsehole.

I managed to free up the bolt from it's cross threading. The spring guides in the gearboxes must differ somehow... certainly the stock bolts are different between the two guns, and now thanks to the combination I can't tighten up either bolt on the tanker stick sufficiently to hold it tightly in place.  It may just need me to shim it with a large nut, or find a shorter bolt.  Or I've lost something!  

 

[Fatboy40]

The stock is giving me the right arsehole.

I managed to free up the bolt from it's cross threading. The spring guides in the gearboxes must differ somehow...

For all the DE M900's I've taken apart the spring guides are the same, but a definite problem is that the rings that hold the ball bearings are made of papier-mâché and can bend at the slightest touch making them a bugger to take out and put back in sometimes.

To help you and others I've about three different spring guides at home that I've tried as replacements for the stock DE one, and every single one is ever so slightly out on size, so use DE M900 users have to look after the stock spring guide as it can't be replaced (unless anyone has found it anywhere as a spare part).

Personally I'm assuming if things ever go bang big style with the gearbox I'll end up having to buy a new quick change gearbox shell and guide

 

[MrTea]

The stock is giving me the right arsehole.

Well that's a brand new sentence I didn't think i'd read today.

 

[RostokMcSpoons]

In the interests of completeness (i.e. stopping my slight OCD from kicking-in, for not posting this), here are my results with the M906C with the ZCI barrel + hop unit on board

View attachment 115353

Basically a 2" group with a couple of flyers.   Pretty good!
I'm not sure why it's looking better than the same barrel + hop + gearbox in the 904G...

Either 

1) The outer barrel is a better fit for this barrel and hop (I certainly felt no need to wrap any tape around it, it's a decent fit with no real wriggle-room
or

2) Twenty shots isn't a good statistical base, and it was down to luck!

I might want to shim the back end of the barrel - that is also a good fit, but the locating rails/ridges on the outside of the hop allow a degree or two of rotation against the inside of the receiver.  If the gun's vibration rotate the barrel that would affect the direction of hop, and therefore the accuracy.  By how much in practice, I'm not sure... but it's something I could address anyway.

I shimmed the stock bolt in the 904G with some washers, that's now fine.  Back-up / family & friends gun now ready to roll!

 

[JVacation]

Glad to hear that the ETU worked well! 

 

[RostokMcSpoons]

Glad to hear that the ETU worked well! 

Yes I've certainly cured the problem, though I did have one moment when I had the same symptom (when I was doing an initial test with the gearbox out of the receiver). This I took as a hint of a possibility that actually the electronics were ok and it's a mechanical problem with the fine positioning of the selector switch.

Regardless, I'm very grateful because the upshot is two working guns ?

Next step is to buy that motor from AK2M4, but I've spent too much on Airsoft recently!

 

[Dan Robinson]

Next step is to buy that motor from AK2M4, but I've spent too much on Airsoft recently!

I have a couple of spare motors, not sure what they are, btu can bring them to next Spec Ops if you're going?

 

[RostokMcSpoons]

I have a couple of spare motors, not sure what they are, btu can bring them to next Spec Ops if you're going?

Cheers!  That'd be good.  I already have one spare Classic Army one that I think is a bit of an upgrade, but it ran hot in the DE (when the control unit wasn't behaving) so not sure if that one is a good idea to try again... an alternative motor would be nice!  

 

[Herrgh]

While both configurations seem effective at close range, further investigation and optimization are recommended to address shimming issues and explore potential improvements in performance. Consider the suggested next steps and tailor them to your specific goals and playing style.

Thanks ChatGPT. I've noticed this account's other posts on this forum are obviously written by a bot, generically replying to whatever the topic is.