WE MP5 FPS Drop

[Cipher-032]

Got a WE MP5 SD (longer inner barrel). Yes I know it’s WE....

I’m getting really poor FPS with Nuprol 2.0. Any thing between 180-230. If I use Nuprol 1.0. I get a far better 300-310. This can obviously be seen in BB trajectory. Another thing to note, is if you fill the mag with a short burst of Nuprol 2.0. It fires far better (Less pressure in the magazine maybe?). Also two of the mags are brand new.

I’ve check nozzle, o ring, rocket valve, check and cleaned the bolt.

Check trigger group, made sure the knocker is fine and moves freely. Tried shimming the hammer spring and that made no difference.

Tried undoing the exhaust valves slightly. No difference.

All I’ve done is fit a new hop bucking, and a Maple leaf 310mm crazy jet.

Any suggestions? Any one had some thing like this before?
Its almost like the hammer spring has suddenly gone weak, or the knocker valves are too strong.
Going by Badabing's video, his MP5 was doing 330FPS stock with the short barrel on propane. So im baffled.

Things im considering apart from making it an expensive wall hanger:
Buy a new Hammer spring
RA Tech NPAS
AMG Ice breaker bulb
Run it on Nuprol 1.0 and forget about it.

Any help/suggestions are most welcome! 

 

[AK47frizzle]

Ye, that's normal with WE mags. You can overfill them and they will spew out tonnes of gas the first few shots. When that does happen, let the mag chill for a bit before firing again and it should be like normal. I think it's due to air already inside the mag when you are filling it. It's hard to drive it out without the gas spewing out first. TM mags solve that issue by driving out the atmospheric pressure inside as you are filling it, as well as the "new" ics gas fill valves. That's why "silent fill" valves are trash.

My guess is that nuprol 1.0 has far less pressure, so the difference between the pressure of air and the gas inside the mag is less.

 

[Wo1f]

Almost sounds like it’s light striking on more powerful gas. 

Was it running fine before the barrel change?

 

[Cipher-032]

Almost sounds like it’s light striking on more powerful gas. 

Was it running fine before the barrel change?

Ill swap the stock barrel back tonight and see.

i agree with you. I noticed on Nuprol 2 it was really inconsistent. On Abby 144a it provides even more FPS and more stable. It’s odd.

 

[Wo1f]

Ill swap the stock barrel back tonight and see.

i agree with you. I noticed on Nuprol 2 it was really inconsistent. On Abby 144a it provides even more FPS and more stable. It’s odd.

That is bizarre. Never had a problem with nuprol gas the couple of times I’ve used it. Good old propane gas never let me down. 

Let us know how you get on with the barrel and we can start to rule things out. 

 

[Cipher-032]

Okay so I made a interesting discovery.

The gun came with a A2, full but stock. All was well until a bought, and fit a A3 collapsible stock. 
 
With the A3 stock fitted. It gives me the poor FPS consistency. The A2 stock doesnt.

I asked on a WE Facebook page and they seem to suggest the recoil rod. But that wouldnt make sense as the gun works fine with the A2 stock.

Mind blown. Guess ill have to contact Milspec and see if I can return it.

Also to add, the first round normally shoots fine with the A3 stock. Its all the subsequent rounds. Which does point towards a bolt seating/cycling issue.

Its annoying as I love the look of the A3 stock.

 

[Wo1f]

Okay so I made a interesting discovery.

The gun came with a A2, full but stock. All was well until a bought, and fit a A3 collapsible stock. 
 
With the A3 stock fitted. It gives me the poor FPS consistency. The A2 stock doesnt.

I asked on a WE Facebook page and they seem to suggest the recoil rod. But that wouldnt make sense as the gun works fine with the A2 stock.

Mind blown. Guess ill have to contact Milspec and see if I can return it.

Also to add, the first round normally shoots fine with the A3 stock. Its all the subsequent rounds. Which does point towards a bolt seating/cycling issue.

Its annoying as I love the look of the A3 stock.

My friend has done this but doesn’t have that issue. Is the spring in the back of the a3 stock like there is on the a2? 

 

[Cipher-032]

My friend has done this but doesn’t have that issue. Is the spring in the back of the a3 stock like there is on the a2? 

Yep the springs there. I bought the A3 stock brand new from Milspec. 

The A2 stock has another buffer below the recoil spring. The A3 hasn’t. I’m wondering if it’s some thing to do with that.

another observation I made was that the recoil spring sits further forward with the A3 stock.