Multi-feed/low fps

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Carta4

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Hi guys,

I recently acquired a CA stoner LMG. 

Im having problems when firing. The rifle spews out a few BB's a time at really low fps and more often than not there is quite a few BB's in the barrel after operation.

The hop unit etc seems in good condition (although I've got another lonex bucking and rubber ordered just in case). 

I have noticed that the nozzle tends to rest in a different place after every burst. Sometimes full forward, sometimes full back and sometimes in between. 

I'm wondering if this can cause the issue and if it is to do with the tappet plate/spring or if it's just normal on the CA stoner.

Any other reasons this could be happening?

Thanks!

 
I would start by checking your hop unit/rubber

as for the nozzle position, in full auto it can stop anywhere even on aeg's.

 
Well that's a relief that means leaving the gearbox alone for now. Yeh the feed lips looked a little suspect and the rubber was highly lubed so like I said I've ordered a lonex bucking and rubber. Hopefully that will sort it. Thanks for taking the time sp00n

 
Unless someone has over lubed the cylinder and every time you pull the trigger it's spraying slippy gunk through the hop... ;)

 
So I've done the paper test on the hop up feed and the paper moves quite alot, I take it this means it's a hop issue? Do you guys know any fixes or should the new bucking do It?

 
If you put a piece of paper or tissue over hop-up within the mag-well and it blew it out when fired, it means you have an air leak which will definitely be causing low fps.  This can be caused by numerous things, including leaks from the bucking, hop-up, cylinder, cylinder head, piston, piston head and air nozzle.

 
So would the next thing to try be a compression test on the mech box?

 
The paper test will show up leaks between the nozzle and bucking. If you have a leak there and feeding issues check the alignment between the nozzle and hop /bucking /barrel. Pull the inner and hop out and peer down the outer barrel. The nozzle should be exactly in the centre.

Also check that the hop is actually pressing down on the bucking. With the inner and hop out of the gun wind some hop on and check you can actually see it protruding into the barrel. You should be able to put enough hop on to make it quite difficult to push a BB past.

 
Yeh the hop rubber adjusts well into the barrel and fully retracts. The nozzle does actually look a little high to be fair. Recommendations?

 
Yeh they are all there. This guy and another vid have saved my ass! I was a bit tentative of opening the gear box but I'm glad I did, I've found the culprit... 

View attachment 22682

 
You've certainly found one issue! Where there's one there's usually more...

 
Indeed guys! It's going to get a damn good clean and potentially a reshim. New cylinder is an SHS 3 steel tooth so hopefully that will hold out. Thanks for all the effort guys much appreciated 

 
You're into the gearbox now, so you might as well do it properly. AOE, shimming, sorting out any other wear...

 
Okay so I changed the piston, cleaned everything etc and got a good compression. New lonex bucking installed so everything should be good but it isn't. Granted it's better but I'm out of ideas. Help?

 
Is the nozzle still out of alignment with the centre axis of the barrel?

 
Yeh but it's flush to the cylinder head which is all aligned in the gearbox so I don't know how to adjust it. What do you think?

 
Every time I've had a feed issue it's been related to the alignment of the hop and bucking with the air nozzle, but I'm unfamiliar with the arrangement in the Stoner. The usual one is the nozzle rubbing on the hop which restricts its movement. The spring isn't enough to pull it fully forward, although sometimes it'll unjam and fire a single round. Otherwise it's alignment front to back. Too far back and the nozzle can't pull far enough out of the hop to allow a BB to feed, too far forward and you don't get an air seal.

It's difficult to see as everything moves so quickly, but if you look down the feed nozzle into the hop does it look as if the air nozzle is travelling all the way forward into the hop?

 
The stoner is very similar to the 249 if you have any idea on that? And I do believe the front to back is sound as it does pull back just enough to feed. It looks like it goes far enough forward but is there a way to make it go further? Also how would I lower the nozzle as it is a little high in the barrel so that could be causing and air seal issue.

 
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