MP5 SD6 bb 'dribble'

FNG

FNG

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Hi everyone,

Thanks for having me. Been airsofting for about 9 months now. My problem. Cyma MP5 SD6 firing on 345 fps, new tight bore barrell, just switched to 7.4v Lipo's (was using 7.4v NiCam before). Having a very good day at Dragons Lair, hitting all I was shooting at, when I noticed something like a 'mis-feed'? Would fire a good burst, then five or six bb's would go about 20 foot and drop. This continued happening, so changed mags (Hi-Cap double mags 560ish bb's) changed battery, but continued to happen. Had a word with the on-site Armourer (good bloke) who advised me to try it on single shot's. Worked perfectly! Switched to Auto and same problem. Armourer advised it was probably air getting past the piston head? Is this drastic (cost?) or is there a simpler reason (hopefully)?

 
Air getting past the piston head, hmm. It does sound like it could be a compression issue, but if it were anything to do with the piston head then there's no reason why it shouldn't happen on single shot as well.

I've not really got any idea what it could be.

I'd advise switching the barrel back to the one you had before, if you stop having the issue, then you know it's something barrel related.

If you continue having the issue then it'll be a gearbox issue, though I can't really think what it could be.

If you can't diagnose a problem, then you have to make it easier by eliminating as many variables as possible.

 
Could it be short stroking? Try lube'ing your piston :)

 
Short stroking would be associated with a drop in compression and ought to happen as frequently on semi auto.

Though it might be that the spring isn't strong enough to fully forward the piston before the gears catch onto it again, giving the effect of short stroking, and that probably would only happen on auto.

You could try getting a stronger spring, a weaker motor, or a lower voltage battery.

What are the fps and ROF? If they are low and high respectively then that's probably your problem. If the above is happening then it could potentially strip your piston after a while. Though as sp00n said, if you lube the living hell out of the piston then it might help it fully forward itself faster than the gears can cycle around and catch it.

Good thought sp00n, I quite enjoy theorising about gearbox issues lol.

Still be best to try the old barrel with it first though, but not before trying it with your old batteries! I'd forgotten you said you'd changed to 7.4v LiPos recently.

System of elimination.

 
Last edited by a moderator:
i meant short stroking as per what Ed said :D as appearing to short stroke, as in ok on semi (long time between cycles etc), rubbish in auto (shorter time between cycles).

like Ed says i would try the old battery ... however it may still appear to do this if your piston/cylinder is dry :( and moving slowly ... no one likes piston'ing dry ..... you know what i mean :P :D :lol:

Ed ... its the engineer in me ... sad i know but its how i am trained to think :o ;) :lol:

 
Gentlemen, Thank you for the replies. I am at Skirmish Billericay on Saturday so will take it with me and try the old batteries as suggested. Will also ask the on-site Armourer to have a look at the lubrecation thing if the battery suggestion doesnt work. Have tried to strip and replace a spring myself unaided on the M4. Gears and tiny springs all over the place! Cost me to get it put right. Its all about the little things in life!!!Practice and more practice. Cannot shoot were I live as in a flat.

 
Actually you can shoot in a flat. Just get a cardboard box, stuff it with an old pair of jeans or similar, then use it as a target from a few feet away. All you are trying to test is if the gun cycles properly, so distance isn't an issue. The box will catch the BBs which you can then chuck in the bin.

 
Like what you are thinking there! Will try it this evening. Thanks again.

 
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