Brand new Cyma Mp5k running over power

[Mattcrx]

Hey all! Looking for some advice.
 

i took my new Cyma blue edition Mp5k to my first skirmish and my gun chronographs at average 356FPS…. it did come down a tad but then fluctuated back up this was using 0.20g BBs so my gun was not allowed.
 

The specification stated 300fps when purchased. Is it because it needs to bed in more? I didn’t fire the gun too much before I took it to the skirmish… 

 

Has anyone got any advice on this please.

 

Thanks 
Matt 

[Tackle]

Might pay to put a few mags through it, sometimes it loosens things up & drops the fps a wee bit. 

Also did you have the hop on or off ?, some sites ask for it to be off for the chrono but that's bs, hop on will reduce fps slightly & it's not like anybody actually plays with hop off, bb's would go everywhere except where your aiming. 

[Mattcrx]

They weren’t bothered about hop up… it’s a fresh gun so probably does need a few full auto mags going through it but.. if it does not bring it down what’s my play? New spring?

 

strange how it was running higher than all h the co2/green gas guns that were there 😫😫

[EDcase]

That's not much over.

Can you test in your garden to set the hop so it fires nice and straight.

This will reduce the fps a bit if the hop was set low.

 

A definite way to lower fps a bit is to set it to auto and pull the trigger quickly so that it stops mid-cycle and leave it like that for a couple of days.

You'll need a chrono to test it though.

[Tackle]

1 hour ago, Mattcrx said:

They weren’t bothered about hop up… it’s a fresh gun so probably does need a few full auto mags going through it but.. if it does not bring it down what’s my play? New spring?

 

strange how it was running higher than all h the co2/green gas guns that were there 😫😫

Just one of those things, people used to say it was a risk when buying in from abroad, but I've seen it & experienced it myself from UK retailers, one could argue they're selling guns not fit for purpose & therefore illegal in some cases, but that's a discussion for another thread. 

Yep you could change your spring, or snip a quarter turn off the fitted one, but I'm assuming it doesn't have a quick change spring system, so that'll be a PITA. 

As @EDcasehas pointed out, getting it to cycle & stop with the piston towards the rear & leaving it that way for a week will compress & weaken the spring slightly dropping a few fps, without a qc box I'd do all the other things mentioned & then get it chronoed before trying to change springs. 

[Mattcrx]

How do I know when it stops mid cycle??  Iv ordered a tracer with a chrono inside so I can keep testing it. 
 

Thanks 

[Rogerborg]

8 hours ago, Tackle said:

Also did you have the hop on or off ?

 

I can't see that this question was actually answered.

 

 

8 hours ago, Mattcrx said:

was using 0.20g BBs

 

<but-why.gif>

 

Indoors, in CQB, fair enough.  Woodland, you'll want at least 0.25g, I use 0.28g.

 

In either case, get the hop set first, then chrono. Everybody else will be doing that, unless you have a weird site.

 

On the bright side, this means you have a decent airseal, so rejoice.  That's impressive energy out of a short barrel.

 

I wouldn't go opening the gearbox, if only because the V3 triggers in these are a sod to get back in place.

 

Just tap the trigger until it starts to cycle but doesn't fire, then leave it like that.

 

If you do want to be sure about the piston position by seeing the cylinder, splitting these things isn't a huge chore.

 

Take out the rear pins, undo the screw behind the magwell and push the pin through, take the small grub screw out of the fire selector, remove one side and pull the selector out from the other side.

 

The receiver will then split along the dotted line.

 

Reassembly is the opposite of removal, plus a lot of swearing as you try to get the fire selector, nozzle and hop unit lined up.

 

 

[Cr0-Magnon]

If I were you, next time you're at the site (obviously not a public place etc), ask them if you can set your hop and then use at at least 0.25g's when you chrono. I don't know of any sites which will prevent you from playing if you're <1.1J on a 0.25g. With such a short barrel you're probably experiencing joule drop (ie what's 1.18J on a 0.20g, may only be 1.05J on a 0.25g).

[Rogerborg]

Yup. My MP5K with the hop set for each weight chronos at about:

 

0.2g = 1.05J

0.25g = 0.95J

0.28g = 0.9J

[EDcase]

6 hours ago, Mattcrx said:

How do I know when it stops mid cycle??  Iv ordered a tracer with a chrono inside so I can keep testing it. 
 

Thanks 

In a normal cycle you'll hear the motor run before it fires.

What you have to do is let go of the trigger as the motor is running but before it fires.

Usually a quick tap will do it but try several times to get the timing.

 

 

Edited March 17, 2023 by EDcase

[Mattcrx]

12 hours ago, Rogerborg said:

 

I can't see that this question was actually answered.

 

 

 

<but-why.gif>

 

Indoors, in CQB, fair enough.  Woodland, you'll want at least 0.25g, I use 0.28g.

 

In either case, get the hop set first, then chrono. Everybody else will be doing that, unless you have a weird site.

 

On the bright side, this means you have a decent airseal, so rejoice.  That's impressive energy out of a short barrel.

 

I wouldn't go opening the gearbox, if only because the V3 triggers in these are a sod to get back in place.

 

Just tap the trigger until it starts to cycle but doesn't fire, then leave it like that.

 

If you do want to be sure about the piston position by seeing the cylinder, splitting these things isn't a huge chore.

 

Take out the rear pins, undo the screw behind the magwell and push the pin through, take the small grub screw out of the fire selector, remove one side and pull the selector out from the other side.

 

The receiver will then split along the dotted line.

 

Reassembly is the opposite of removal, plus a lot of swearing as you try to get the fire selector, nozzle and hop unit lined up.

 

 

Thanks for the great advice! I’ll have to look into hot to set the hop properly because if I’m being honest other than seeing if it shoots straight I have no really knowledge on how to that.

 

iv just bought the Acetech BT tracer with a chrono so I can keep tabs on it and try and get it down a few pegs. For a beginner gun it’s been quite impressive.

 

 

 

 

When I read the manual it says that if it’s away from the hop it’s off… mine is pretty much all the way out if not all the way out… so maybe my hop isn’t set at all… 🤷🏽‍♂️😂

 

thanks for the hell’s guys! Sorry I’m such a noob at this.

[Rogerborg]

12 hours ago, Mattcrx said:

other than seeing if it shoots straight I have no really knowledge on how to that

 

Ouch, sorry for coming across as peremptory - I forgot that we've all had to figure this stuff out from the very basics at one point.

 

You'll definitely want to get your hop dialled in before doing chronoing.  When doing that, you'll want to use the BB weight that you're intending to play with on the day.  0.2g is fine for short range CQB, and especially if you're using tracers indoors.  Outdoors, go as heavy as your hop can lift, and your wallet can afford.

 

It may very well be the case that your hop unit doesn't need much pressure applied to lift 0.2g.  Apologies, I don't have a dial-style hop on my MP5, I have the very short MP5K with a slide-lever unit, which is quite fussy - a tiny nudge can result in over or under hopping.  Your dial may be the same, and I hear tell that they like to wind themselves off in use.

 

What's important is to have as much range as possible to test with, so that you can see the terminal behaviour. With your 1.2J+ gun you can shoot out to a real-world 50-60m, and should be able to get a flattish trajectory for most of that.  It can be tricky to see exactly how your gun is shooting when you're the one on the trigger, and having someone else standing off to the side to watch the BB trajectory can help.

 

There are loads of opinions about ideal hop and trajectory.  I personally like to see the BBs lifting just at the end of their flight so that I can be sure that I've got sufficient hop on.  As in, over-hop slightly, then dial it down just a touch.  Here's one I memed earlier.

 

 

And as above, if you put a few hundred BBs through your gun, or leave the spring cocked for a bit, it should settle down. Chronoing with (properly hopped) 0.25g or heavier BBs should also sort you out.  There's even a difference between a cold spring on its first shots of the day, and the same spring after putting a mag through it.  I reckon your MP5 will be fine if you just get a little creative with it.

[Mattcrx]

14 minutes ago, Rogerborg said:

 

Ouch, sorry for coming across as peremptory - I forgot that we've all had to figure this stuff out from the very basics at one point.

 

You'll definitely want to get your hop dialled in before doing chronoing.  When doing that, you'll want to use the BB weight that you'd intending to play with on the day.  0.2g is fine for short range CQB, and especially if you're using tracers indoors.  Outdoors, go as heavy as your hop can lift, and your wallet can afford.

 

It may very well be the case that your hop unit doesn't need much pressure applied to lift 0.2g.  Apologies, I don't have a dial-style hop on my MP5, I have the very short MP5K with a slide-lever unit, which is quite fussy - a tiny nudge can result in over or under hopping.  Your dial may be the same, and I hear tell that they like to wind themselves off in use.

 

What's important is to have as much range as possible to test with, so that you can see the terminal behaviour. With your 1.2J+ gun you can shoot out to a real-world 50-60m, and should be able to get a flattish trajectory for most of that.  It can be tricky to see exactly how your gun is shooting when you're the one on the trigger, and having someone else standing off to the side to watch the BB trajectory can help.

 

There are loads of opinions about ideal hop and trajectory.  I personally like to see the BBs lifting just at the end of their flight so that I can be sure that I've got sufficient hop on.  As in, over-hop slightly, then dial it down just a touch.  Here's one I memed earlier.

 

 

And as above, if you put a few hundred BBs through your gun, or leave the spring cocked for a bit, it should settle down. Chronoing with (properly hopped) 0.25g or heavier BBs should also sort you out.  There's even a difference between a cold spring on its first shots of the day, and the same spring after putting a mag through it.  I reckon your MP5 will be fine if you just get a little creative with it.

 

No man the advice is brilliant I didn’t take any offence haha! Mines the slide type Hop. I have a feeling my hop is off. So I’ll try and get a decent amount of space and try and dial that in as best as I can.

 

Just a recap, you suggest I should use 0.25s instead of 0.20s? I do mainly play CQB at the moment. 
 

Thanks again for all your help. I left the spring cocked ( pressed te trigger until the motor sounded but didn’t fire and i am going to leave it for a few days. Hopefully my tracer chrono will arrive so I can keep taps on averages etc. 

 

again thanks very much for your time and help! 👍🏽

[EDcase]

Don't worry, we all started as boobs noobs 😁

 

For CQB 0.2g is fine.  (The tracers will come in handy too)

 

When you play in woodland 0.25 or 0.28 will work well.  You'll have to adjust the hop of course but easy to do at the site range.

 

 

Edited March 18, 2023 by EDcase

[Rogerborg]

Yup, 0.2g is fine indoors, and tracers are great fun. It's just that 0.25g will likely produce a lower energy value than 0.2g due to your short barrel (with longer barrels, it tends to go the other way).

 

I'd err on the side of over-hopping at the start of the day, because if you can see some lift on the BBs, then you can be sure that you've got at least enough hop on, and it'll bring the energy down.

 

Our slide style hops can be prone to creeping off, if the screws aren't done up tightly. This is what your hop and barrel will look like out of the gun - there's a screw on each side holding the slide on, and if you ever have it apart, it's worth checking that they're snug (but not too snug, they're metal self tapped into plastic).

 

 

The other thing you can do is to whip a small cable tie around the barrel and the end of the hop slide and pull them tightly together. You should still be able to move the slide, but it'll add some tension and help to hold it in place.  Once you know exactly how you want it set up, you can put a little piece of grip-tape, a sliver of pencil eraser or something similar between the barrel and slide, then cable tie them together again to hold it very securely in place.

 

I'd stress that none of this is necessary, it's just things that you can do if you want to have a fiddle and try to get it optimised. MP5Ks are great for CQB right out of the box, you've made a very solid choice.

 

 

[Mattcrx]

15 hours ago, Rogerborg said:

Yup, 0.2g is fine indoors, and tracers are great fun. It's just that 0.25g will likely produce a lower energy value than 0.2g due to your short barrel (with longer barrels, it tends to go the other way).

 

I'd err on the side of over-hopping at the start of the day, because if you can see some lift on the BBs, then you can be sure that you've got at least enough hop on, and it'll bring the energy down.

 

Our slide style hops can be prone to creeping off, if the screws aren't done up tightly. This is what your hop and barrel will look like out of the gun - there's a screw on each side holding the slide on, and if you ever have it apart, it's worth checking that they're snug (but not too snug, they're metal self tapped into plastic).

 

 

The other thing you can do is to whip a small cable tie around the barrel and the end of the hop slide and pull them tightly together. You should still be able to move the slide, but it'll add some tension and help to hold it in place.  Once you know exactly how you want it set up, you can put a little piece of grip-tape, a sliver of pencil eraser or something similar between the barrel and slide, then cable tie them together again to hold it very securely in place.

 

I'd stress that none of this is necessary, it's just things that you can do if you want to have a fiddle and try to get it optimised. MP5Ks are great for CQB right out of the box, you've made a very solid choice.

 

 

Thanks guys!
 

So more hop = lower velocity? So technically if my hop is off that could be a real reason why it’s over powering? 
 

Im going to set the hop as best as I can and hopefully after putting a few mags through it it calms down. 
 

Regarding the hop slide altering itself iv read quite a lot about this happening so I will be sure to tighten that up and secure it. 
 

Thanks again guys! Brilliant help! I’ll keep you all posted.

[Colin Allen]

4 hours ago, Mattcrx said:

Thanks guys!
 

So more hop = lower velocity? So technically if my hop is off that could be a real reason why it’s over powering? 
 

Im going to set the hop as best as I can and hopefully after putting a few mags through it it calms down. 
 

Regarding the hop slide altering itself iv read quite a lot about this happening so I will be sure to tighten that up and secure it. 
 

Thanks again guys! Brilliant help! I’ll keep you all posted.

Yes, the slider style hop units in particular tend to have a significant impact on velocity; more hop = less velocity.

[Mattcrx]

Ahhhh! This may be my biggest problem

[Rogerborg]

On 19/03/2023 at 01:53, Mattcrx said:

So more hop = lower velocity? So technically if my hop is off that could be a real reason why it’s over powering? 

 

Yes, generally.  Of course with it being airsoft you'll get the occasional exception where a gun wants a little bit of pressure in order to get a perfect airseal, but yes, more hop = less energy for the same amount of puff.

 

 

On 19/03/2023 at 01:53, Mattcrx said:

Im going to set the hop as best as I can and hopefully after putting a few mags through it it calms down. 

 

With the tendency of hops to go off, or to work differently depending on temperature, I always do it on site, just before chronoing.  Sometimes I'll re-adjust at lunch, or even in game if it seems peculiar.  If you're not sure, give it a little more than it needs, so you can see a definite upwards arc.

 

 

On 19/03/2023 at 01:53, Mattcrx said:

Regarding the hop slide altering itself iv read quite a lot about this happening so I will be sure to tighten that up and secure it. 

 

It's a particular issue with MP5s, either the slide unit like that, or the non-K models with a rotating lever. In both cases, the solution is to add more friction, you'll figure it out.

 

[Mattcrx]

11 hours ago, Rogerborg said:

 

Yes, generally.  Of course with it being airsoft you'll get the occasional exception where a gun wants a little bit of pressure in order to get a perfect airseal, but yes, more hop = less energy for the same amount of puff.

 

 

 

With the tendency of hops to go off, or to work differently depending on temperature, I always do it on site, just before chronoing.  Sometimes I'll re-adjust at lunch, or even in game if it seems peculiar.  If you're not sure, give it a little more than it needs, so you can see a definite upwards arc.

 

 

 

It's a particular issue with MP5s, either the slide unit like that, or the non-K models with a rotating lever. In both cases, the solution is to add more friction, you'll figure it out.

 

Thanks mate! Great advice!! I’m back to a skirmish on the 30th so I’ll let you know how it all goes 

 

thanks again Matt 

[Mattcrx]

So… moving the hop made it fire a hell of a lot faster. 
 

So here is the results from my Acetech tracer BT. 
 

I have tried leaving the spring engaged  for a while and put a fair few mags through the gun and it’s still firing high. 
 

As you can see from the results the 352 FPS is with no hop at all as soon as I start moving the hop slide in towards the magazine it fire a hell of a lot faster.
 

So what options do I have now? Use 0.25g BBs?? 
 

Thanks again guys! 
 

 

[Rogerborg]

On 20/03/2023 at 11:36, Rogerborg said:

Of course with it being airsoft you'll get the occasional exception where a gun wants a little bit of pressure in order to get a perfect airseal

 

Well, am I glad I added that caveat.  Phew, that's a spicy little boi and no mistake.  I honestly wouldn't have expected that from such a short barrel, although CYMAs M4 and AKs do run hotter than UK limits by design, and need down-sprung for the UK market.

 

So what I'd assume here is that you've got one with something like an M120 spring in it that should have been down-sprung by the importer or retailer. No harm in asking them if they want to sort it as a warranty issue - it isn't fit for the purpose sold.

 

If they laugh it off, it does seem like you'll need to replace or cut the spring, and disappointingly it doesn't have a quick-change spring, so it'll be a gearbox out and open job.

 

It can be quite intimidating the first time you do this, but it's not really that complicated. Just take it slowly and keep all the parts safe.

 

Disassembly to the gearbox:

 

 

 

This is a very comprehensive guide to working on a V3 gearbox. And yes, the trigger spring can be a bit of a sod during re-assembly.  All you really need to do is to get it open and change the spring without touching anything else, but while you're in there you could lube and re-shim it (there are plenty of videos on that too)

 

 

[Mattcrx]

That’s a brilliant guide… not sure what spring I’d need to replace with… 

 

would simply using 0.25bb not bring it down under the 350?

[Cannonfodder]

43 minutes ago, Mattcrx said:

would simply using 0.25bb not bring it down under the 350?

No. The muzzle energy would be the same as increasing the weight means your max fps is lower. If a site is allowing players to use guns firing at 350 fps on heavier bbs then it needs to be avoided as the people running it obviously don't know what they're doing

[Nick G]

I was just about to answer that , beaten to it ! 😂