Cyma mp5 sd6

[ghillieguy10]

Hello,

I recently had my gun 'upgraded' by a 'gun doc' and im having some issues. The gun will not fire properly on the first 20 shots of each mag, often jammin or the bbs just drop 20 feet away. This was not happening before the work was done, but now is impeding my play. im using Cyma metal midcaps and goldenball .25g bb on a 330 fps gun. it has 3 rnd burst and semi, neither of which work until part way through the mag. i have not checked the hop up yet as i was wondering if it could be the bb or the mag

[Bellerophon]

Your description is really vague: what kind of work did this 'gun doc' do? Have you tried taking it apart yourself?
Other than that, this sounds like either a dirty barrel or ripped hop up rubber. Remove the barrel and hop up rubber, check the barrel for dirt and scratches, check the hop up rubber for rips, wear and good seal. Clean the barrel with a small square of cloth and a cleaning rod, and if you find any problems with the rubber then just buy a replacement.

Side note: continuing to fire after a jam to dislodge a stuck BB is a TERRIBLE idea and might ruin your barrel's inner surface finish.

[ghillieguy10]

Sorry for being vague, replace the motor, gears, a gate merf mosfet, piston cylinder and cylinder head

I jave not checked anything yet as I was looking to see what the issue could be. Before I started looking. A good side note is I dont open aegs often, only bolt actions

[Bellerophon]

Ok, fortunately the checks I suggested do not involve openning the gearbox. If your MP5 SD is anything like mine, the barrel and hop up rubber should be accessible just by removing the handguard and popping off the little plastic C clip on the hop up chamber.

The only other possible thing I can think of that could explain your problem is if the tappet plate/nozzle was reinstalled incorrectly, causing problems chambering BBs and reducing compression to the point it can barely fire. checking for this problem will require openning the gearbox and so I'd suggest doing the other two things first.

[ghillieguy10]

Okay but if it was tappet and nozel would it still shoot well after the first 20 or so. And what mags/ bb do you use

[Bellerophon]

If it were the tappet/nozzle, every shot will be inconsistent. You may hit a streak of good shots, but it would quickly stop working again.

Also: try loading a few BBs into your mags and then release them by hand. If they come out of the mags dirty or broken, the mags are at fault and the feed track needs to be cleaned.

I don't know what brand mags I use, I bought my MP5 as a package deal on the classifieds. As for BBs I use BBBastard .28 nonbio and Madbull .28 bios. I have no idea how good goldenball BBs are, so here are the tests I use to determine if a BB is any good:
1. Inspect the surface for mould lines, pits or lumps. The surface should be perfectly smooth and glossy in finish.
2. Crush one BB in pliers. It should squish before breaking, not shatter.
3. (not strictly relevant here, but good practice for evaluating any brand of BBs) Cut a few BBs in half and make sure there are no bubbles or gaps in the center. If there are any, these can throw off your accuracy because of the uneven weight distribution.
4. If available, use some calipers to check the diameter and tolerances of a few sample BBs, and ensure these dimensions match those on the packaging. If the packaging specifies tolerances wider than +/- 0.01mm, or worse they don't give tolerances at all, the BBs are probably crap.

Hope that helps.