The two pins of my switch wouldn't stay together at first; no misfires. I applied Locktite and I believe it insulated the pins from each other, so misfires ensued. I installed the brass shim & the misfires stopped & has been 99.999% reliable since. That tells me it was an electrical improvement. Wish I would have taken measurements, but my coils tell me all I need to know - I have only tiny voltage drop.
The shim also took out the play or rattle in the switch, and created a much smoother action. For me it was like a $5 sw turned into $25 one. I applied a single drop of fishing reel oil (the thin stuff, not the grease) into the body of the switch, hoping to reduce reactions between dissimilar metals since there are now 4 diff. metals making the switch: spring, body, brass pin, steel button, brass shim. This isn't the greatest stainless steel, as you can tell by holding a magnet to the device. It's fairly attracted, so there is still a decent amount of electrical reactivity in the metal & corrosion control should become part of your routine maintenance all over this device. It's not out of hand, but just pay attention to exposure to salty environments & flesh eating e-juice.
I also put a tiny drop of locktite onto the outside threads of the switch body, inside the MKB to prevent it from ever unscrewing completely unless effort is applied. BTW use medium strength locktite (blue color, NOT Red!). Although I have the small sw lockring very tight it has tried to skirt out on its own a few times. Loosing the switch would be a severe bummer.
There are two rod stock sizes that have been used successfully to replace the standard 1st issue floating center pin, during our lengthy discussion (my fault): 1/8" and 1.14mm diameters. The metric size was a little more dead on. I can't take credit for anything because it has always been an ability of a real GG to push the atty connector pin up into an adapter. So we mimicked that, and I think I was 2nd at that. There are certainly advantages to having a single solid connection. Namely, less volt drop, & mechanically/electrically more sound as its less likely to .... out & short with less segments.
OR... I'm not a fan of permanent modifications, but I'm in possession of a brass 6-32 female insert. I'm more than tempted to chuck the insulator that came in the MKB, and fill the void with epoxy putty encasing this brass insert, replacing the role of the unthreaded factory insert. I could then use a knurled-head brass 6-32 screw through the insert forming a new adjustable center post of the atty connector. Man, now that I wrote it down, it sounds like a better idea than ever. This would allow adjusting position on the fly w/o a tool and control the pressure on the atty, since I am finding my current pin hits my Terminator slightly off-center and I think it's breaking my seal. Also I'm paranoid about poking a hole in the top of my battery and blowing my face off. I should also mention the downside of a single long pin makes it less convenient to use cartos in the collection tank (no adapter). It's just another type of vape, and the MKB showcases the true possibility of a carto by airflow and excess juice management. You can push the pin back into the battery bay for a carto but I'm not fond of that much loosey metal inside with my batteries & I feel an elevated paranoia over a battery puncture that way.
You may use the original pin for a single solid connection - just push the SS pin out of an eGo connector, leaving the insulator inside, screw it on the MKB and push the MKB pin up watching to see the insulator seats ok. That's a really easy way to test out changes w/o dire consequences & figure if you want to get more radical. Please use a fuse, or a kick, or some kind of overcurrent protection if you choose to perform these mods since an 18650 is at the size I begin to fear what a battery can do. Seriously. Or at least have a multimeter that you know how to use for continuity and check for shorts BEFORE energizing. Sorry I come off opinionated all the time. Experience has made me this way.
Well, I hope my word splat helps answ. a few ques'ns. Eventually I think we'll get all this represented in photos & I see a sticky in our future. I'm only 1/2 done modding this modable mod. I'm out-of-town for the weekend, so see 'yall next week.
Info I'm after... Vego, can you post some close up pics of the MKB adapter? I'd like to see what you are saying about your pin falling out, etc.