ARP 9 can't feed for shit.

[Skara]

Okay, I am about to throw the whole hop/barrel assembly in a dumpster and set it on fire...

Stock nozzle, stock chamber, Prometheus blue rubber (no internals from factory), Prometheus bridged flat tensioner, stock barrel: double feeds once every 6/7 shots. In particular it chambers one bb, doesn't fire it, chambers the next and fires both at 5 metres.

Same setup but with a 185mm barrel: the same.

Same setup but with a modified G&G green rubber, both barrels:

Same. Fucking. Issue.

What on earth am I missing?

It happens both in semi and full auto, with CA midcaps, G&G high cap and G&G drum.

Please help

 

[Adolf Hamster]

Does it do it the same on a freshly filled/wound mag as a near empty one?

 

[Skara]

That is a test I haven't done yet.

Will report later.

 

[Skara]

Update.

With midcaps it fires around 40ish shots before misfeeding.

With the stick high cap does pretty much the same.

With the drum fully wound it works fine until the spring is almost out of tension.

 

[Adolf Hamster]

Is she stock speed? I'd normally have expected the opposite- misfeeding on a fresh mag.

If it doesnt have one already a sector delayer chip is always a good shout, as is making sure the tappet spring has plenty of strength.

That said i wouldnt expect that out of a stock arp box.

 

[Skara]

I tested it with a 7.4v, which gives a slower ROF than the recommended 11.1s (still misfeeds)

What I have noticed is the "firing pattern":

it goes 1-1-1-1-1-0-2-1-1-1-1-1-1-0-2 (so it both misfeeds AND double feeds, yay)

So there is something that at some point prevents one bb from being fired.

When I replaced the nozzle I checked the tappet spring and it was fine.

Anything else I shall try?

 

[Adolf Hamster]

definately no binding on the tappet? ie moves nice and freely if you just press it in from the outside?

the only other thing i'd be suspecting is the hop rubber, i've had some issues with misfeeds from maple leaf rubbers due to the longer feedlips, maybe the prometheus you're using is doing the same?

thing is that normally manifests with a weak mag spring (eg when a midcap is near empty).

 

[Skara]

definately no binding on the tappet? ie moves nice and freely if you just press it in from the outside?

the only other thing i'd be suspecting is the hop rubber, i've had some issues with misfeeds from maple leaf rubbers due to the longer feedlips, maybe the prometheus you're using is doing the same?

thing is that normally manifests with a weak mag spring (eg when a midcap is near empty).

Yep, moves freely and smooth as silk.

It does the same with a G&G green rubber.

I'll try the Prometheus purple when it gets here and an old Ares clear green one as well to check if it's a lip issue.

 

[Skara]

Okay, I will exclude any hop rubber/barrel issues.

Played with some more hop/barrel combinations, including the aforementioned Prometheus Purple and Ares soshititdoesntevenhaveaname one.

Also tried a Prowin hop unit but of course it doesn't fit.

I only have to play with the nozzle lenght now. I do not have spare nozzles and ordering them would take ages due to festivites.

How can I test what lenght would I need without actually having extra nozzles?

 

[Adolf Hamster]

If its the stock length i'd leave it alone.

You could strip the springs from the box, reassemble with the nozzle forward then turn it over to see how far back it retracts.

Possibly a worn tappet plate? Might be worth looking when she's open especially if she's got a high round count.

 

[Skara]

Round count should be around 10k bbs fired since I bought it, add a couple K from the previous owner.

I'll pick up a Modify tappet plate and see if I can get a new spring at the local retailer tonight and see what I can do.

If that fails, I'll hand it over to a tech.

 

[Skara]

Of course the arp tappet is proprietary.

Ffs.

Screw this, I'll take it to a tech.

 

[Adolf Hamster]

Of course the arp tappet is proprietary.

Ffs.

Screw this, I'll take it to a tech.

Is it? Thought it was just a standard v2 box....

Tbf last time i had one open i was more concerned with picking bits of schredded spring out of it.

 

[Skara]

Is it? Thought it was just a standard v2 box....

Tbf last time i had one open i was more concerned with picking bits of schredded spring out of it.

The plate is narrower than a standard v2 modify one towards the nozzle, by a lot. It's like a third of the width, and the shell is different.

View attachment 52366

 

[Adolf Hamster]

Makes sense, musta just not picked up on it when i was in there. Tbf if it aint broke and it aint my gun i have a habit of not fixing it.

 

[Skara]

Turns out to be a magazine issue.

I need to change all the springs...

 

[Skara]

Let's necro!

Having some free time I disassembled the mags and gave them a nice clean.

Somehow things have worsened, as they now feed ONE bb per mag.

New springs it is then.