Fixing Nozzle Misalignment AKA "Midcap Syndrome"
 

Does your gun feed perfectly with hicaps, but when your midcap has more than 70 rounds loaded your gun lobs BB's 10 feet? You either have nozzle misalignment, or a nozzle timing issue. Simply put, the upward spring pressure from the mag can pushing the air nozzle up, and out of alignment with the hop up. What this means is that instead of the nozzle sitting inside the hop up sleeve lips, it causes a fold in one of the corners. This can lead to simple FPS issues, but can also lead to hop up pinch jams which will cause damage to your piston and gears. If you are experiencing nozzle timing issues, the symptoms are very similar. The issue is the upward pressure is slowing the nozzle and it is not loading the BB in time. The piston is being released before the BB has been chambered and before the nozzle has mated properly to form a seal with the hop up lips.

There are three ways to correct this issue:
-Increase tappet spring tension
-Use a hop up rubber with thinner lips and a wider opening
-Use a nozzle that is more tapered or rounded at the front
-Reduce nozzle wobble

Spring Tension

The easiest way to resolve this issue is to cut a few coils off your tappet plate spring, then re-make the hook using pliers. This will fix the issue in most guns. The problem is that occasionally I will see broken tappet plate springs from the poor quality of springs found in AEGs and the increased tension from shortening the spring.

I have finally found a solution to this issue. I have sourced much stronger tappet plate springs. They are made of much better metal, the metal is much thicker, and there is a LOT more tension. Make sure you have a good tappet plate because it will increase chance of breakage on polycarbonate tappet plates.

Hop Up Lips

For a rubber with thinner lips, my go to rubber is the VFC stock. Unfortunately changing rubbers also means changing your hop up setup unless you're running a R-hopped barrel, so I'll go into some detail regarding the other two issues to correct.

Nozzle Taper

The following picture has four different air nozzles.
http://i34.photobucket.com/albums/d1...pse2aff80f.jpg
Left to right:
Retro Arms, taper enhanced
VFC original
VFC, taper enhanced
Core

As you can see, the VFC original nozzle has minimal taper. This is why many VFC AEGs start having this issue when you start changing hop up parts around. The taper basically helps the hop up lips to conform to the orientation of the nozzle.

These instructions will assume you don't have a lathe. If you have a lathe, you probably don't need instructions. To retaper a nozzle, first remove the O-ring.
http://i34.photobucket.com/albums/d1...ps3564887a.jpg

Next, find a sacrificial cylinder head with an undersized nozzle to seat your air nozzle on. G&P cylinder heads work well for this. Make sure it can spin VERY FREELY or you will ruin your nozzle.

Stick your nozzle on the cylinder head, and get some 400 grit or higher sandpaper. Hold your cylinder head at an angle, and sand diagonally, probably more sideways than forward. Make sure your nozzle is free spinning while it is being sanded, otherwise you will ruin it. Make sure pressure is very light.

http://i34.photobucket.com/albums/d1...ps8f6ec855.jpg

When you are done, the sanding should be even all around, and your taper will be enhanced. If you have done this properly, you will not experience any FPS loss.

Nozzle Wobble

My solution to nozzle wobble, is to buy 10 different nozzles, 10 different cylinder heads, and then get 20 different O-rings. Mix and match until you find the combinations that result in the least wobble.

Unfortunately most people aren't willing to do that, so the easiest way to make what you have work, is by flaring the end of the cylinder head nozzle to stabilize the air nozzle.

Put your nozzle on your cylinder head like so, and test the amount of wobble you have in the fully forward position.

http://i34.photobucket.com/albums/d1...ps363730e2.jpg

If the tip of your air nozzle is wobbling by more than half a millimetre, proceed to the next step. Otherwise you're probably okay.

Take something round and conical that can fit inside your cylinder head. I use a pair of needle nose pliers. GENTLY put it in and spin it around to flare the cylinder head.

http://i34.photobucket.com/albums/d1...psc88d26e4.jpg

Test wobble again, and repeat the method until your wobble is less than half a millimetre. MAKE SURE YOU DO THIS GENTLY AND SLOWLY. IF YOU OVER DO IT YOU WILL HAVE RUINED YOUR CYLINDER HEAD.

Hope this helps some of you guys.

-Z

Awesome.
I have the same method of fitting air nozzles, buy a shitload of them lol

Great writeup. This needs to be a sticky.

Another Tidbit to remember on this issue is to make sure the nozzle, where it fits to the tappet plate, is tight and does not wobble or fall out easily. The more play you have in that fitment the more chance you have of the nozzle being pushed out of position.

Tighter is always better ;)

I've found that tappet plate fitment has little to no effect on nozzle wobble due to the natural flex in the tappet. The tappet also needs to be loose fitting in the gearbox itself otherwise it will get stuck, so it will wobble with the nozzle.

It does however affect FPS consistency as back and forth play will affect where the BB seats in the chamber.

I am referring to where the nozzle slides into the front tappet groove (not the tappet plate itself), sometimes the nozzles are tight and level with little lateral movement (the tappet and nozzle become almost like one solid piece if it fits well), other times you can see significant nozzle play and any upward spring pressure on that nozzle at full extension will push it out of alignment. A tight fit in this groove counteracts this pressure and does not let the nozzle flex upwards as much.

Yep I know what you're talking about, I'm saying that the tappet being long and thin flexes a lot by design so it has minimal to no effect on nozzle wobble. The only way it would help with upward nozzle wobble is if it were too tall and pressed the back of the nozzle up on to the cylinder head, but then you'd run into tappet timing issues from it getting stuck. An aluminum cylinder head won't flex.

It should be noted that there is such a thing as too much taper relative to the hop rubber.

Awesome post. Just had a convo with someone having issues with a mid cap until it has less than approx 70 BB's in it. I'll be sure to send a link for this to him.

Thanks

I have been dealing with this issue for a year and a half... On my second aeg now. A VFC MK18 and receantly had a massive fps loss. From 340 with a m90 down to 240:( Im thinking its the nozzle. So far.....

Great post Z

Post has been updated with another possible diagnosis + fix. Nozzle tension issue described and remedy added.

Nice work!

Either I accidentally posted the wrong part number from McMaster Carr, or the SKU changed. Part number has been updated the the correct one as of 2017-04-11

Great info! Encountered this problem numerous times and always thought of the best way to fix it. Thanks for taking the time to share!

Hey, the SKU for the Spring at McMasterCarr disappeard. Can someone send me a link to the item? Would be very happy:) Kind regards!