Src mp5 A4

[Busydad]

Hi, hoping for some advice on upgrading Src mp5 A4. The gun hasn't been touched since brought 4 months ago second hand. It's firing at 270 fps with a 6.03 tight bore barrel. I contacted src who said that the mp5 comes with a m105 as stock. My question is has the original spring gone weak & needs replacing for another m105 spring or do i need to fit a m110 spring & if so do I need to upgrade gearbox internals? I would grateful for any advice.

[Prisce]

I don’t think you need to look at the spring yet. What fps do SRC say it should be shooting at stock?

 

Firstly, before looking at your spring, I’d spend some time learning about the air seal and compression(if your confident enough to work on the gun yourself-if not send it to a tech to have a look- ask for a service)

 

If SRC day it should be shooting 340fps, which I think is reasonable with an M105 spring, you are loosing air somewhere, find this and you’ll solve all your problems.

 

If after sorting this, it’s still low, you probably need a new spring. What length barrel is the SRC using?  You should be able to run any spring up to M120 in a standard box.

[Busydad]

Thanks for your reply, src say that the mp5 should give around 330  fps. I will strip it down to try & find any air leaks. Will replace air nozzle whilat stripped for one with internal seal. The barrel is a ZCI 6.03mm 230mm long.

[Prisce]

Then yeah I’d imagine you have an air leak somewhere, so you know about the compression tests? The paper test etc?  Try some of these first, it may be the hop rubber and barrel seal, could be the cylinder needs lubricating.  

 

Try the “free” methods first, then go onto the replacement parts.

[Busydad]

I do know about the tests thanks, although never tried them.in person. Thanks for your help, like you say start with the free stuff, didn't think it could be a air leak though. I was ready to replace the spring without any tests. Thanks again for your advice. 

[Prisce]

Anytime.:)

[Busydad]

Stripped my src mp5 gearbox over the weekend & could only find a slight air leak from the air nozzle which I replaced for a new one with a o ring fitted. Changed the green plastic bushings for metal, resealed cylinder head, new piston o ring, shimmed gears,cleaned & re greased everything. With doing all that the fps has only gone up 15 fps, so firing around 285 fps. When i asked SRC which spring is fitted to their mp5's they said m105. I brought the mp5 second hand & was told it was only 6 months old. Is it worth changing the spring for another m105 or try a m110 spring? I also don't know if SRC miss informed me as I can't understand how a m105 just gives 285 fps on a un ported cylinder. Any advice would be great as I'm a bit stuck on what spring to get.

[MisterG]

Have you checked for oil in the hop up and have you checked the bucking?

 

If the issue is not the spring, a new one won't fix it.

 

Cheers

G

[Busydad]

Thanks for your reply, I've checked the bucking & cleaned it & the hop up. Also did the Teflon tape mod on the bucking. 

[dazzer306]

SRC MP5's have one downside to them, magazine fit, I have two G&G MP5's, an SD type ( brand unknown) plus a metal bodied SRC, plus about 10 various makes of mag inc SRC and G&G, all the mags fit the G&G and unknown perfectly, but when it comes to SRC here's the problem, only SRC ones fit with on problem, others are a very tight fit, I've even sanded down some of mags to get to fit but are still very tight, this just a heads up .