Double Eagle M906C - Internal upgrades / tinkering

[RostokMcSpoons]

I'm starting a new thread as I've been trampling over other people's too often recently, and as I've got my own chrono and a desire to do the simple things on my own, I thought I'd record stuff here, and ask for related advice.

Background:

New Double Eagle M906C delivered start of November.  Didn't open it up to clean it out, just straight off to three skirmishes where it's performed very well in-game but with two caveats:

1) Low rate of fire on 7.4v.  Especially so after a cold day on the field.  In warm conditions it's shooting 11.6 rps on 7.4v, 16.4 rps on 11.1v.   That'll do me.

2) Low muzzle velocity.  Very variable figures seen, anything from a low of 230fps on a very cold site, to 300fps in my house, but also down at 270fps in the same conditions.

The odd thing about the muzzle velocity differences are they stay consistent each time, so each day / test the readings are all very similar, within +-5fps 

Intended actions:

1) Crack open the receiver, check the gun looks ok internally

2) Spray some lube into the nozzle (leave for a while, then shoot it out before re-assembly)

3) Change stock hop rubber to 50C (Light green) Maple Leaf Macaron 

4) Change stock hop nub  to Omega 

5) Change spring to M100 or M105

'Before' testing:

With gun at room temperature, chrono'd at 270-280fps.

Accuracy test with cheapo BB Kings 0.25g Bio BB's, 15m measured, fired from room @ 19-20C, 2C ambient temp outside, light wind, bench rest, Kobra red dot, approx 30 shots
View attachment 82980

Results:

1) I've cracked open the gun...
The front receiver pin was stiff and it took some hammering, but very easy to slide off the top receiver after that (once I'd worked out the dust cover needs to be closed, or it'll get blocked by it).

No damage to the nozzle.

Barrel was quite clean, but not perfect, so ran some cotton swabs through it.
There's evidence of light greasing on the piston - everything looks good (neither under or over lubed) to my untutored eye

2) Sprayed the Ultrair silicon lube into the nozzle and left it while I did everything else.   Then blasted out the excess with a few shots before reassembly.

3) Replaced the hop rubber.  The old one seemed fine, lubed on the outside but clean-ish on the inside.  It definitely worked ok as I've managed to over-hop 0.30g BBs a few weeks ago.

4) Attempted to replace the nub.  The Omega is simply too large to fit into the hop arm...
View attachment 82822

Have I bought the wrong one somehow???  @ak2m4 perhaps you could tell me?

5) Replaced the spring.  This was really easy thanks to the quick-change system.  (I wish my TM AK had the same, breaking the gearbox open was a real pain and left me with a bill for someone else to put it back together!) 
The stock tube bolt needs a long-shafted no4 Hex bit to undo.  The spring end plate thing needs as wide a flat-head screwdriver as you can find (to make it super-easy).  The spring guide is nicely engineered.
The interesting thing is I've tried two springs in there:

Action Army M100 - much shorter than the stock spring, gave 320fps with 0.25g BB's (no hop)
ASG M105 - either longer than the stock spring, or about the same length... it's still in the gun so can't compare now... 320fps 
Which just goes to show you can't trust the manufacturer's ratings, gotta try the springs yourself. 

And the acid test, 0.20g BBs with a bit of hop applied ... 345-350fps.   Yaaaasssssssss!

So, I'm really rather happy.  I've successfully 'done things' without apparently buggering-up my gun, mostly thanks to the nice way it's been designed and built by DE.
And the muzzle velocity is up to the site limit, and still seems to be consistent.  Though obviously it's changed from day-to-day before, so I'll have to keep my eye on that!

I'll re-test the accuracy tomorrow, but obviously I'd rather do it with the Omega nub in place.  Still, it'll be interesting to see what difference the other changes have made first.
I'll also chill the gun outside, see if that affects the fps.
 

 

[Adolf Hamster]

looks like the stock hop nub (red bit) is a weird proprietary shape, but it also looks like if you slide it out sideways the omega nub will sit normally in the arm. reckon that extra bit of material that's in the top is to stop the nub from falling out (which is the inevitable outcome of cutting corners and not dissassembling the hop before pulling the barrel with a standard nub)

normally i'd caution against spring changes until certain the air seal is pretty consistent, as a low energy reading could be an adequate spring losing most of its puff to an air leak, but sounds like 'borgs silicone down the nozzle trick has helped a bit in that regard (also possible the macaron feedlips are sealing better to the nozzle)

 

[RostokMcSpoons]

Oh I see what you mean, so I forego the security of the retaining part, but it'll still work! Yeah, I'll give that a go!  Tomorrow... my wife is demanding my return to the sofa...

I must admit, I'm not confident about the muzzle velocity.  I'll want to see it chrono consistently for at least a couple more days before being reasonably sure it's fixed.

Top tip for anyone putting the stock tube back on, and completely confused on how to manoeuvre the silver bolt retainer into the right location and orientation (especially with the wiring getting in the way) - put the bolt through it before dropping it down the tube - the extra weight stabilises it and gravity becomes your friend
 

 

[Adolf Hamster]

Oh I see what you mean, so I forego the security of the retaining part, but it'll still work! Yeah, I'll give that a go!  Tomorrow... my wife is demanding my return to the sofa...

yeah, that extra bit of a nub is a neat idea, but tbh i've never found issue with the standard setup as you just install the barrel before the nub and hop arm.

I must admit, I'm not confident about the muzzle velocity.  I'll want to see it chrono consistently for at least a couple more days before being reasonably sure it's fixed.

its a tricky one to gauge, generally when pulling the box fully apart to do it a lot of it still based on feel anyway (well, at least if you're going for the basic static check).

generally chrono is the best quantative measure- lower the fps dispersion the better

 

[Fatboy40]

Oh I see what you mean, so I forego the security of the retaining part, but it'll still work! Yeah, I'll give that a go!

Your hop unit arm is different from that in my DE M904E, mine 100% did not have the cut-out that held a bump on top of the cylindrical nub. I've just dug the Maple Leaf packet out, from under my computer desk, that the old nub is in and it's just a cylinder of black rubber with a hole through the middle (no retaining "bump" on the top).

And what Adolf said is 100% spot on with the nub ?

Also my youngest son's getting an M906C for Christmas, so it will be interesting to see what's inside of his when he lets me crack it open (ML bucking and nub are the first thing I'll tweak for him before he plays with it in anger). Also at some point you might have to crack the gearbox open and re-grease the piston head O-ring, I had to do this on mine recently to get it back to the FPS it had out of the box.

Lastly I'm finding that the QD spring guide is getting harder to remove and re-insert each time, the metal ring that's holding the ball bearings in place appears to be slightly warping, I think a sign of the cheaper build quality and materials used by DE. I'm going to take a punt on one of these in the New Year...

https://www.maxxmodel.com/cnc-stainless-steelaluminum-spring-guide.html

... also, just in-case you're wondering, I'm not trying to hijack your thread, just wanting to help out another M90X buddy 

 

[RostokMcSpoons]

Thread hijacking?  Nah, appreciate the interesting info ?. And I've sidetracked enough threads myself that I can't complain even if you did ?

 

[RostokMcSpoons]

(Damnit, can't edit my last post, the emojii on the end seems to confuse the editor) 

I was going to ask, is the lack of a slot on the bottom of that spring guide going to cause an issue?  Will you be able to rotate it ok with just pressure on the base rather than leverage from a screwdriver blade?

Question about the accuracy...

As I've just received my F2000 but I'm torturing myself by waiting until Christmas morning to unbox it, I ended up watching Airsoft Mike's review again last night.  Yeah, I know... but he is the only person who has done a full review of the Cyma version, so 'any port in a storm'

I'd previously dismissed his accuracy tests as looking like it was too short-ranged to care about, but when I listened he said it was at 50ft, and that's 15m, same range as I tested my gun at.  His results with the F2000 were impressive tbh, much tighter grouping than I got. It's raised the question: is the F2000 inherently that much more accurate because of the longer barrel, him shooting indoors with perhaps better BB's etc... Or was my gun underperforming?  How are you guys finding the accuracy in your guns?

Edit:

I've now fitted the Omega nub.  It was a little more fiddly than with that cunningly shaped stock nub, as I tried several times and must have positioned it a little too far back so it was perhaps jamming on the edge of the 'window' and failing to apply any hop.  Once I'd got it in the right place I fired a few shots down the garden.   A very small sample stats-wise, but the shots seemed to fly straighter.  Looking forward to repeating the accuracy test later!

Chrono tests this morning are the same, yowzers, I'm a happy bunny.  I have to put some hop on to get it below the 350fps but that's fine isn't it?

 

[Adolf Hamster]

I'd previously dismissed his accuracy tests as looking like it was too short-ranged to care about, but when I listened he said it was at 50ft, and that's 15m, same range as I tested my gun at.  His results with the F2000 were impressive tbh, much tighter grouping than I got. It's raised the question: is the F2000 inherently that much more accurate because of the longer barrel, him shooting indoors with perhaps better BB's etc... Or was my gun underperforming?  How are you guys finding the accuracy in your guns?

the ammo may well be playing a part in it, good quality ammo is as essential to an accuracy based build as any amount of hop rubbers/barrels etc, likewise removing wind from the equation won't hurt.

barrel length alone generally isn't too important, at least not within the extremes (ie stupid long or stupid short). generally the other factors (quality/weight of ammo, air seal, correct voluming, hop and barrel quality) are more impactful. generally there's not much reason to worry/mess with barrel length outside of the needs of the gun to look appropriate to its real world counterpart.

 

[RostokMcSpoons]

Cheers Adolf, see my edit above - possibly accuracy has improved with the new nub in place.
I'll test it properly soon, using both the same BB KIngs ones for a direct comparison, and also the Specna 0.28g Bio BB's that I just bought a big batch of (hoping they're alright!)

 

[Adolf Hamster]

Cheers Adolf, see my edit above - possibly accuracy has improved with the new nub in place.
I'll test it properly soon, using both the same BB KIngs ones for a direct comparison, and also the Specna 0.28g Bio BB's that I just bought a big batch of (hoping they're alright!)

iirc i think specna's bb's are supposed to be decent enough. you might want to look up a chap called gasman on here did a bunch of testing on bb's a while back.

i always went with geoffs, usually .3's or .32's for assault builds, pricey but it's amazing how many "feed issues" i've fixed over the years by swapping out the ammo in the magazine to them.

 

[RostokMcSpoons]

Yeah I was using Geoff's when I first came back to skirmishing because I remember having problems with my AK's tight-bore barrel with cheap ammo.

I've now tried a few different makes in my DE... KWA, ASG, BB Kings, and the Geoff's.   They've all worked ok, no feeding issues I can remember, but obviously there could be differences in the accuracy that I wouldn't have noticed during games.  Hence my attempt to punch a few holes in paper to see how the gun is performing.

Geoff's are quite pricey while the Specnas are £8 for 6000 at the moment, which is cheap enough to make me look past any issues

https://jdairsoft.net/deals/day-4

Edit: 

More chrono results today (Thursday) - still 345-365fps depending on hop.  Yay!
I had to drive to the airport and back and lost the afternoon due to traffic, it was getting dark and raining when I got back so haven't done any more accuracy testing, or left the gun to get cold.

 

[RostokMcSpoons]

Quick accuracy test this morning... new spring, bucking and nub

Not quite got everything dialled in by the looks of things... and maybe the rubber still has some silicone oil on it (from the cylinder/nozzle), though it does appear to be applying hop successfully.

Accuracy test with cheapo BB Kings 0.25g Bio BB's, 15m measured, fired from room @ 19-20C, 7C ambient temp outside, no wind, bench rest, Kobra red dot, approx 30 shots

Chrono'd at 345fps with 0.20g (with hop applied), 300fps with 0.25g

View attachment 82981

The main cluster is tighter, but the slightly larger and much clearer aiming mark I've used may have helped with that... so inconclusive (or no real change)

(Also tried a mag ostensibly full of 0.28g BBs loaded up at my last game, but it chrono'd at the same 300fps so I'm thinking it was the same ammo.  
Same result too - big cluster at top-right with a few flyers, some of them quite wild)

Is the fact I'm now grouping slightly further to the right an indication I've not quite got my barrel rotated with the nub at TDC?  Is that possible?

 

[Adolf Hamster]

Is the fact I'm now grouping slightly further to the right an indication I've not quite got my barrel rotated with the nub at TDC?  Is that possible?

it is possible, a clear way to tell is if you see your shots consistently curving (not linear, a pronounced curve) in one direction, means the backspin is being applied at an angle, generally easier to see at longer ranges.

the nub *should* stay at tdc (depending on how tight the nub is to the hop body, and how tight the hop body is to the outer barrel) but if the barrel is slightly rotated then the corresponding mound on the bucking will be lop-sided. generally before final assembly good to look down the barrel with the hop partially on as it'll be visible.

the other possibility is there's been a shift in zero during rebuilding, which would be if they're not noticably curving to one side.

 

[RostokMcSpoons]

it is possible, a clear way to tell is if you see your shots consistently curving (not linear, a pronounced curve) in one direction, means the backspin is being applied at an angle, generally easier to see at longer ranges.

the nub *should* stay at tdc (depending on how tight the nub is to the hop body, and how tight the hop body is to the outer barrel) but if the barrel is slightly rotated then the corresponding mound on the bucking will be lop-sided. generally before final assembly good to look down the barrel with the hop partially on as it'll be visible.

the other possibility is there's been a shift in zero during rebuilding, which would be if they're not noticably curving to one side.

It's 'only' an inch and a bit off, but given how solidly the gun goes together I wasn't expecting anything to shift to spoil the windage zero.  Which is why I suspected the hop.

I think I'll put my old 4x32 scope on the gun (something I could have tried before) to see if I can spot any deviation at the last moment - there was nothing obvious with the trajectory to me looking through the Kobra sight (but I do have crap eyesight with these specs!).   

Edit:  Just tried the scope, so I can clearly see most of the shots are good, but with a few curving either way, with more to the right than to the left when they do curve.

 

[Adolf Hamster]

It's 'only' an inch and a bit off, but given how solidly the gun goes together I wasn't expecting anything to shift to spoil the windage zero.  Which is why I suspected the hop.

the hop is definately a prime suspect, generally the curving effect becomes more pronounced with range as the bb slows down and is more reliant on lift, reckon it'd be difficult to spot at that range and you're only seeing it because you're being so thorough with using a target.

if it were me, i'd pull the barrel and take a close look at how the contact patch is sitting, it can be very subtle.

you might also want to check the fps range, eg if you're averaging 300fps on that ammo what's the ± fps range around that average. generally that's a measure of air seal and a factor in vertical dispersion, although there's also the range of ammo weights (ie ±Y grams around the nominal X gram average weight) that can affect this.

 

[RostokMcSpoons]

the hop is definately a prime suspect, generally the curving effect becomes more pronounced with range as the bb slows down and is more reliant on lift, reckon it'd be difficult to spot at that range and you're only seeing it because you're being so thorough with using a target.

if it were me, i'd pull the barrel and take a close look at how the contact patch is sitting, it can be very subtle.

you might also want to check the fps range, eg if you're averaging 300fps on that ammo what's the ± fps range around that average. generally that's a measure of air seal and a factor in vertical dispersion, although there's also the range of ammo weights (ie ±Y grams around the nominal X gram average weight) that can affect this.

I'll take another look at the hop system, once I've done my Xmas shopping ;D

The fps min max is pretty stable now, especially with the 0.25's and hop applied, the last few shots were 
302.3

301.5

301.3

302.6

(Unfortunately all the rest of the shots on my chrono history are a different gun, but I remember the other ones were all around 300-302 as well)

 

[Adolf Hamster]

The fps min max is pretty stable now, especially with the 0.25's and hop applied, the last few shots were 
302.3

301.5

301.3

302.6

that's pretty damn good, if it can maintain that level of consistency then that's a great start.

interesting to see how the specna 0.28's are performing with that setup.

 

[RostokMcSpoons]

Just for completeness,  here's the accuracy test with ~30-35 shots with the Specna 0.28g BBs.  It's a breezy day compared to my previous attempts, so that may be why the grouping includes a few flyers, but there's also a pleasing hole in the paper. 

I also had my 4x32 scope on the gun.  Scientific 'method' gone a bit out of the window tbh, but it ensured I had a good aim.  None of the shots were poorly taken, they occasionally just curved left or right (maybe the wind, maybe the hop still slightly askew)

So...
 

Accuracy test with Specna Arms Core 0.28g Bio BB's, 15m measured, fired from room @ 19-20C, 13C ambient temp outside, gusty wind, bench rest, 4x32 scope, approx 30 shots (probably a few extra)

View attachment 83167

Chrono results for 10 shots with 0.20g Gold Fire BBs (with hop applied). 
348.6 (high)

341.7

345.6

338.5 (low)

346.7

345.8

346.4

342.5

342.7

346.3

And with the 0.28's

280.1

278.4

276.8

279.0

278.7

280.1

280.8

278.6

280.7

279.0

(I've got more but they're all 278/279!)

I've got to be happy with the consistency with the 0.28's

I suppose the good news to take away from my experience thus far is that changing bucking + nub and spring seem to have settled the consistency of the power output, in warmer conditions at least, but the accuracy isn't massively improved.  So presumably the DE bucking and nub are actually fairly decent (excepting the possibility the bucking didn't like the cold and was affecting the muzzle velocity)
 

 

[Adolf Hamster]

worth checking the fps consistency on the specna's as well. one of the quality elements of good ammo is weight consistency (and by extension velocity consistency) for a given energy.

generally stock hops on a lot of guns aren't strictly bad, issue is they're just not intended for the combination of heavier ammo/colder climates.

hard to tell from just the grouping if it's wind or natural dispersion in the horizontal, but the vertical looks decent.

 

[RostokMcSpoons]

worth checking the fps consistency on the specna's as well. one of the quality elements of good ammo is weight consistency (and by extension velocity consistency) for a given energy.

Yeah, that second bunch of chrono results are the Specna 0.28's, so around a 3fps variance!