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Define "properly"? All it is is to chop off the head of the hop unit. I tested using a Marui, WE, REAPs rubber all with the same result on the MP5, with and without the Ring to stabilise the hop rubber. It needed heavy BBs, and while range is higher, FPS is lower even with BB weights kept consistent. On examination the nozzle width is shorter than the hop rubber breech opening, the airseal is very poor.

The VSR mod doesn't work either on both the M4 and the MP5 Airseal is poor, loss of FPS, BBs rolling out the front. I am sticking to the flat hop mod on the VFC hop rubber and the AEG nub, seems to get the best consistency out to 50m. In the case of the M4 I use the Madbull blue bucking. 400fps for MP5 and 450fps for M4 CQBR.

The Crusader Feedramp adds a noticeable consistency to the FPS, and keeps the mag wobble free. That is a must. I haven't been able to find a azimuth nozzle one but my metal pin insert is keeping my stock one working over a few thousand rounds. Don't get the Angrygun nozzle. I find that the bolt guides decreases recoil speeds, and doesn't really keep the bolt dead centre. But I will continue the test.

AFAIK original HK is baked enamel paint, no phosphate and no bluing.

Bare metal receiver: If it is blued then should provide some protection , or if the receiver is aluminium, which the MP5 is not.

Sounds odd. There are two things which would push the bolt down. One is the piece of metal that pulls the bolt back during the firing cycle. The other is the feed ramp. Can you take pictures of your bolt and BCG and push your bolt head upwards while taking a picture from the side of the gas port?

So with the mag out this issue doesn't occur?

Otaroko Can you take a picture of the broken nozzle? I want to analyse the cause of fracture.

I don't get it, when you pull back the BCG to a point the BCG will pull back the nozzle.

Sitting high can be a good thing so long as the return to battery closes the bolt. It ensures a good seal between blowback unit and the magazine. I am having the opposite problem where the mag is sitting too low on a V1 M4 receiver and a V3 nozzle/bolt set.

Just did a partial axle replacement with an AR15 hammer/trigger pin as a preemptive measure. Surprising it is the same diameter as the original pin hole. I feel like an Orthopedic Surgeon right now LOL Anyone have a picture of any other mechanical failures on the MP9?

I don't have a photo, but here is what I can do in MS paint, by no means a CAD drawing but its as good as Paint can get for technical drawings. http://arniesairsoft.co.uk/forums/index.php?/gallery/image/15103-we-g39e-barrel-fix/ This also requires free floating of hand-guard to the outer barrel by removing the tabs from the hand-guard which slides onto the gas block. I used a soldering Iron to melt the tabs and then chiseled it out.

Telfon deforms over time. I use aluminium sheets from coke cans between the outer barrel and barrel breech interface, and between the Trunnion and upper receiver. I use an AR Barrel shim on the barrel nut. No wobble after that.

Yeah but the hand guard hides the inaccuracy. Basically if you push the foregrip left and right the fall of shot will shift, which is NOT what we want in any rifle. Ideally you need to free float the barrel so that no matter how you apply pressure onto the handguard it doesn't affect the accuracy in any way. There are three sources of inaccuracy in the G39E outer barrel system: - Outer barrel to barrel breech interface - Barrel breech interface to barrel trunnion - Barrel Trunnion to receiver. The barrel nut will only fix the 2nd problem, which can be fixed using an AR15 bar

I dunno how much of the FPS discrepancy is due to the nozzle. My nozzle is pretty much stock. I removed the Angry gun one I will be machining a brass nozzle tip for it to custom fit the hop unit. By machining I will be using my drill as a lathe and using a hand file to trim. The FPS fluctuations cannot be the interface between the gas routing the blowback unit because I installed a crusader feedramp and there is pretty much no wobble. I also don't know if it is the nozzle as my nozzle doesn't really catch on things. But I will check again. I still get a variation mostly around 40

Wow ok, that was simple. But mean while I will keep with my flat hop mod, I am getting good consistency atm though FPS output seems to be inconsistent which is what is causing the erratic hop... I just installed an Angry gun nozzle, FPS dropped from 400fps to 250fps. Its pretty much junk. Any one has a similar experience? Whch nozzle should I get?