Brand new Cyma Mp5k running over power

[Mattcrx]

Yeah so if I ran 0.25g BBs my muzzle energy would need to be even lower to equal the max 350 of the site. I get it. 
 

so looks like iv got to change the spring! How annoying 😫

[Nick G]

350 fps on .20's is 1.132 j    on .25's youd need to be at about 315 fps or lower

[Cannonfodder]

38 minutes ago, Mattcrx said:

Yeah so if I ran 0.25g BBs my muzzle energy would need to be even lower to equal the max 350 of the site. I get it. 
 

so looks like iv got to change the spring! How annoying 😫

That's correct. Here's a handy chart to show what the muzzle energy is for different weight bbs at different fps limits

[Rogerborg]

1 hour ago, Cannonfodder said:

No

 

Maybe. Short barrelled guns can experience what I'm just about to coin as "Joule leak".  I get sharply dropping energy in my MP5K as I move up to heavier BBs.  It's worth a try, although I still reckon it'll want the spring cut or swapped.

 

Since we don't know what's in it, I can't recommend a replacement. I'd guess that it's got an M120, so anything in the M100-M110 range (maybe up to M115) might do it.

 

Always remembering that there are no standards in airsoft, so one brand/production run of "M100" could be radically different from another.

[Cannonfodder]

While it might happen I wouldn't want to rely on it to get the gun site legal

[Rogerborg]

9 minutes ago, Cannonfodder said:

While it might happen I wouldn't want to rely on it to get the gun site legal

 

Oh, I totally agree. It's shooting so hot that I'd want to get it down substantially with a spring change or cut, particularly if it's going to be used in CQB.

[Mattcrx]

It’s a Cyma CM.041PDW blue edition. It’s actually crazy that the power it is running is with the hop OFF! If I put the hop fully on it’s hitting 372s… 😳 

 

I shot 1001 rounds last night and it did drop to 348s (hop off) and I thought brilliant it just needed bedding in… however this morning it’s straight back to 352s. Maybe the drop in power was battery going flat or everything starting to get warm etc… I’m not sure. 
 

Thanks again for all the advice guys! Looks like I’ll be stripping it myself or sending it to davescustomairsoft… 

 

 

 

 

Here some readings when I shot the 1001 BBs last night 

 

you can see where it hits 360s 370s as I’m putting the hop on. 
 

The last image is when it settled quite nicely but that’s after 1001 BBs

 

 

[Rogerborg]

9 hours ago, Mattcrx said:

It’s actually crazy that the power it is running is with the hop OFF! If I put the hop fully on it’s hitting 372s

 

Just to be absolutely sure, which way are you sliding to add hop?

[Colin Allen]

20 hours ago, Mattcrx said:

Yeah so if I ran 0.25g BBs my muzzle energy would need to be even lower to equal the max 350 of the site. I get it. 
 

so looks like iv got to change the spring! How annoying 😫

No,  the muzzle energy, measured in Joules, could be the same; the velocity would have to be below 313 FPS when using a 0.25g BB.

313 FPS on 0.25g = 1.13J
350 FPS on 0.20g = 1.13J

Sites should really measure in Joules rather than quoting a velocity based on a 0.20g BB, which hardly anyone uses.

[Rogerborg]

16 hours ago, Colin Allen said:

Sites should really measure in Joules rather than quoting a velocity based on a 0.20g BB, which hardly anyone uses.

 

Insert Stock Rant #3 about "lol m8 evry1 noews wut 350 meens m8".

[Cannonfodder]

14 hours ago, Rogerborg said:

lol m8 evry1 noews wut 350 meens m8".

You'd be surprised 

[Rogerborg]

10 hours ago, Cannonfodder said:

You'd be surprised 

 

I wouldn't be at all surprised, I've seen plenty of folk on Facebook ask "wut bb wait 2 get undar 350?" entirely sincerely.

[Colin Allen]

7 hours ago, Rogerborg said:

 

I wouldn't be at all surprised, I've seen plenty of folk on Facebook ask "wut bb wait 2 get undar 350?" entirely sincerely.

That would include the chap that I met at a site the other week; I tried to explain to him that using 0.28g BBs at 340fps was not acceptable but he was not having it.  Watching him try to argue it with the chrono marshal and then the site owner was amusing.

[Mattcrx]

 

On 26/03/2023 at 10:27, Rogerborg said:

 

Just to be absolutely sure, which way are you sliding to add hop?

I’m sliding the hop towards the magazine as the slide says HOP-> which I assume put hop on.. pullin out towards the muzzle is hop off

Edited March 28, 2023 by Mattcrx

[Rogerborg]

23 minutes ago, Mattcrx said:

I’m sliding the hop towards the magazine as the slide says HOP-> which I assume put hop on.. pullin out towards the muzzle is hop off

 

Yup, that's right. I didn't want to prompt the answer.