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Sako

down on power query...

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Noticed my rif is a little down on power the past day or so, fully charged 9.6v nimh battery fitted (brand new, charged on a vapex), seems it's incapable of penetrating even a cereal box from 5 meters, any possible suggestions? Prior to this it was going through both sides of a thick storage cardboard box. However the gun is cycling well and sounds fine. Any ideas would be appreciated

Thankyou

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This involve stripping down the gearbox? I'm actually new to owning my own RIF, so not sure entirely of all the terminology/parts.

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What gun is it? The M&P15?

 

First step Look into the magazine well and fire a few shots on semi auto, you should see the air nozzle moving back and forth each time you fire (the bit which feeds a BB into the Hop unit and creates the air seal against the hop rubber). If its NOT moving on each shot then its a gearbox problem involving the tappet plate. If it IS working ok it sounds like an air seal leak somewhere as said in Lozarts reply, so check the Hop unit is firmly seated into the gearbox (on an M4 look through the ejection port or mag well with a torch if necessary).

 

M4's usually have a spring around the inner barrel pushing the Hop unit against the gearbox which allows a small amount of movement - it is worth seeing if you can push the hop unit forward a few mm with your finger, then release it so it sits properly against the gearbox and try a few BBs through the gun- when you insert the mag look at the Hop unit through the ejection port and see if moves as the mag clicks into place as the mag can move the Hop unit forward and reduce the air seal- long shot but it may cure the problem.

 

-Are you using the same mag as previously?

 

If the above all looks and works ok and the gun sounds the same as before the problem occurred it could be the Cylinder air seal which is a full strip down job. Likewise if the Piston has stripped some teeth, but this would sound horribly different. If its a new gun I'd suggest taking it back to the retailer to check over if the above simple checks don't highlight the problem.

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I will go and check just now, you certainly know your onions! Thankyou for taking the time to reply.

 

Chris

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Ok, had a look and the nozzle is moving fine when firing, I can't see if the hop is seated correctly to be honest. When you say to press the spring for the hop up do you need to remove the gearbox from the receiver?

The problem only started after I bought a new hi cap mag and now it's all the time, even going back to the original, I thought it was just coincidence though? Gun was flawless up until then.

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Ok, had a look and the nozzle is moving fine when firing, I can't see if the hop is seated correctly to be honest. When you say to press the spring for the hop up do you need to remove the gearbox from the receiver?

 

 

With the gun upside down, looking into the magwell, you'll see the feed tube on the hop unit (where you can see the nozzle going in and out). Put your finger in behind the feed tube (ie towards the stock end of the gun) and push the feed tube forwards. It should return under spring pressure. Basically, above the barrel is a little spring which pushes back against the inside of the receiver to ensure the barrel and hop unit is seated firmly on the front of the gearbox. What MAY have happened is the hi-cap has somehow unseated the hop slightly causing an air leak around the end of the barrel. Pushing forward and letting it come back should re-seat it.

 

If it doesn't, you don't need to remove the gear box, but if you release the upper receiver by removing the large frame pin just under the delta nut (the bit that holds the handguard on) and pulling the receiver forward you can remove the upper reciver completely (loads of vids on YouTube for this by the way). Once you have the receiver off you can take a look down the inner barrel to see if the hop rubber has been disturbed or is obstructing the end of the barrel.

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Update.

 

I have full power perfect shots if I put pressure on the mag when shooting, I gently pull the bottom of the mag toward me (so gently putting forward pressure on the top of the mag internally). And it shoots full power each shot...hop up issue??

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Stripped the receiver down and had a look at hop up, seemed ok, put back together and it seems to be functioning ok again, think it may have been my cheap hi cap had pushed on the feed nozzle/hop up unit and put it out of place causing an air leak path...sticking to pmags!

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Sorry forgot to say, it's actually the Pmag that was causing the problem, not the king arms mag (had them mixed up), I should have realised that the Pmag was such a tight fit and pushed the feed nozzle/hop assembly away from the gearbox.

 

Just a heads up if anyone has an issue with power that conveniently coincides with a change of magazine...also worth taking the upper off and giving the hop tension spring a little stretch too I've noticed.

 

Hope this maybe helps someone else in the future.

 

TAGS: low power hop up moving magazine change different spring air seal problem issue

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Just to note, I've gone ahead and completed the o-ring mod on the hop unit (placing several 5/16" ID o-rings over the inner barrel down to the front of the hop to give greater press onto the GB/air nozzle area reducing air leak paths).

 

With this mod completed I have noticed the hop won't budge at all and is accepting ALL the different mags I have without any issue.

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Nice one, was just about to post saying its worth putting rubber/nitrile O rings round the barrel so it won't move forward as I had a similar problem when using different mags with a couple of M4s; as you've found too, its this movement which has caused most problems with low power issues for me in the past.

 

Cheers,

Martyn.

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