Thanks McKee, I'll give that a shot as well.

I was so stoked when i got it but the fact that I have SOOO many mags and non of them worked right was a big piss off. I think im going to throw that fish back in the ocean, or that gun back in the classifieds LOL

Alright so update here. Gamed my gun this Saturday and realized despite lubing the hop-up and shimming the magwell with velcro, the problem still exists.

My theory: It's for sure an issue with mags being filled to capacity. Arkell has a G&P XM177 but the same magazines (MAG VN midcaps) and has the same problem. I was loading them to approx 90 rounds (as indicated on my TM speed loader) and had to regularly shoot the first 8-15 rounds out before they would shoot straight. The gun shoots 400fps normally. The first rounds shoot around 180 until it fixes. Shooting upside down makes no difference.

I believe that the tension in the mag springs is such that when it is full loaded, the BB in the chamber is forced up against the top of the hopup with enough force that as the nozzle loads the BB it drags across the top and has enough friction to slow the BB substantially.

Any help with this issue would be appreciated.. somebody somewhere must have noticed this before.

This is a very common problem. As midcap capacities continue to go upwards, spring strengths have to increase somewhat too. The PTS PMAGs and TMAGs are well-known offenders. Interestingly enough, my Madbull TROY mags have 190 round capacities and do not seem to have this issue. I've run into overly strong mag springs in a variety of AK and M4 mags. I've seen several AEGs that have a nozzle/tappet subsystem that falls victim to this issue.

The thing is, you kinda *want* strong springs, since we all want good feeding at full auto, and we want good feeding with more friction/spin-producing BBs.

A solution to this problem which has been widely-observed to work is to strengthen your tappet return spring by removing a couple of coils. My usual solution is to cut two coils and then bend one more coil to create a new spring loop to hook the tappet to the gearbox shell. Make sure you take care to use a large wire cutter and to secure the coil while doing this to ensure you don't have your coil fly across the room.

+1. I've had to do this to pretty much ALL of my AEGs...

I'll just add that it's my belief that many many compression, feeding, BB-brand, bucking, barrel, hopup unit and mag issues are really just this problem, but mis-diagnosed as other issues.

Sorry....maybe it's just me. How does the spring pressure inside the mag cause air-leak/compression issue type symptoms?

I think he means the tappet spring is the cause not the mag spring.

Many ways.

The bbs could press up against the nozzle hard enough to cause air leaks between the nozzle and cylinder head. Basically, like a prying motion.

The bbs might press up hard enough that the nozzle doesn't seat completely forward and gets caught on the upward force of the bbs. Hence, why you increase the strength of the tappet spring to pull the nozzle back into proper position. I believe this is the symptom and cure Maciek is referencing and honestly makes the most sense in this situation. As the tension in the mag goes down, the nozzle moves more freely given its current tappet spring tension. As the nozzle moves more freely, rounds load better and the nozzle seats properly.

In two piece cylinder head setups the nozzle and cylinder head may not leak under the pressure, but the pressure on the nozzle may stress the two piece cylinder head where the nozzle meets the head (probably not very common) or where the cylinder head meets the cylinder (can also happen in 1 piece). This is probably fairly rare unless your cylinder head/cylinder is really poor quality

I notice that in tappet plates, there is play in where the nozzle sits. In the standard design, there are many areas for leakage in the interactions between just the nozzle, cylinder head and hop up. The fact of the matter is that the nozzle not only operates as a means to deliver compressed air to the bb but also to restrict bbs from entering the chamber. As a result, the entire load of the rest of the mag sits against the nozzle. If you release a fully loaded mid cap, you know how much force this has (hint: use eye pro). All that pressure on one small part that really isn't completely secure itself. That's where these issues arise from.

I believe Maciek has a good write up about this issue on his SIG and its very long nozzle.

(By the way, I know you probably know most of this, the length of this write up was for any other people who find this thread and want more info.)

Cheers!

Both are the cause actually. But really it's all our fault.

The key insight here is that if a given problem doesn't happen on a stock Tokyo Marui gun, it "doesn't count" as a design flaw. As soon as you start jacking up different variables across the compression or gear transmission subsystems in the Marui design, all sorts of strange and out-of-spec behaviour starts to appear. Big surprise, eh ? ;)

Now I'd love to go smack the engineer who thought it would be a great idea to strongly-couple the forward seal to the feeding mechanism, but he has a great excuse for his mistake: Stock Maruis don't have to produce Canada-ready velocities, nor do they have to contend with "high cap" midcaps from Taiwan.

No doubt about it though, as soon as this design had to contend with 120+ rounds pushing against the nozzle, having high trigger response from strong LiPos and also producing 360fps (or higher) in compression, it was going to show some cracks. There you have it.

And it's probably no accident that:

1) the mag that comes with that gun has a fairly weak spring and
2) it is rated for around 300fps.

I probably mixed things up after skimming through the posts...just seemed like McKee's post related a velocity increase to mag spring strength.

Most of the poor FPS air leaks that I've seen attributed to the magazine feed hole not being spaced out/aligned properly with the feed tube of the hopup unit. The hopup unit will be forced out of position and there'll be a resultant airleak at the nozzle/hopup rubber junction.

I definitely know that FPS values can be really low initially, especially in cold weather, as some warming/loosening up is needed. Ripping off a burst of full auto (BBs or not) before chrono'ing is a good idea if the temperatures are cool. But it should be just the first blast after the gun's been cold for a while...not at the start of each mag.

I'll reread this thread more carefully, thanks

The strong-mag-spring-weak-tappet-spring bug can happen in setups that have completely secured hopup units with good "nozzle-bucking kiss", so this is a new distinct issue that you can add to your catalog of infuriating problems with AEGs :)

Don't you just love AEGs?

After years of wrenching on them...frankly I got bored of them.

The only electric guns I would bother with are LMG/SAW's and PTW's.