Argyld

slight adjustments: install NPAS More FPS: tighter or longer barrel less FPS. less powerful gas, shorter barrel

I think the heaviest for a stock MWS was 0.28, maybe 0.30 Heavier and you need a to change the hop-up rubber.

Do they fly to right in a straight line, or do they curve to the right. Basically you aim at point and they consistently impact at the same point but to the right, adjust sights. I can never remember but I think when you hit right, you adjust to the left. If they curve/turn midflight then the Hop-up is probably misaligned. I would ask the store where you bought it do adjust this. Note: if your BBs are only fliying a few feet, you need to adjust your hop-up.

A high power valve will increase your FPS, but also your gas efficiency (less shots from the mag). I would take a tighter/longer barrel. You get more FPS, but still have the same gas efficiency. Also if get new mags, no need to change the valves on those to get them to the same level as the other ones. Search this thread, there were plenty of posts detailing which barrel length or inner diameter was used to get 400fps

Short answer: nothing Slightly more detailed: Check your FPS with a chrony and be aware that GBBRs FPS vary with outside temperature. The hotter, the more FPS. In Winter (<10°C you might want to switch to Red gas) Your nozzle return spring might break after a few thousand shots. General GBBR: clean and lube regularly, search in this thread for tips and what to use. Ollie talks Airsoft youtube channel is also a fantastic source for MWS related stuff.

This might justify paying a mini plumber pipe cutter, you know 🙃 Remember to thoroughly clean the tube afterwards, don't want any particles getting blown through your nozzle/barrel.

Not the best idea. The oring blocks a small hole which vents air from the mag. If there is air in the mag, it can escape via this hole, making place for gas. When gas spews out of this hole, it means your mag is full. If you block this hole with an oring, air cannot escape, reducing gas capacity or you have to manually vent the mag. I know we Airsofters are used to tinkering with our RIFs, especially AEGs, but in this case TM put quite a lot of thought in every detail, and if something is as it is, there is a very good reason for it. Have a look at Ollie talks Airsoft YT-Channel, he has at least one vid on how to fill a mag correctly. Not saying you are doing it wrong 😉, but with the vid you can compare it to your spitting problem. If it looks the same, it is normal, just means the mag is full of gas, any excess is vented out. (Not sure why you wouldn't have this with propane though)

The fill valve is installed at a slight angle, when the bottom of the mag is straight, the valve is not. Tilt the mag slightly, till the valve is upright (have a closer look at the fill valve, you will see), then you can get some more gas in. But I don't think that will solve your problem, only 10 shots without tilt, seems too low. If you never tilted your mag when filling with propane and it worked fine, it is the WE gas (can). What type is the WE gas (green gas, red gas) or what PSI does it have. What was the temperature when you were playing. Week gas with (very) low temperature, might explain it.

Why? I carry enough mags (6) during a game so that you not have to refill BBs. I don't play milsim types of game. Games might take 1-2 hours. Running around with a rattling speed-loader isn't fun. To get to your actual question, cut the tube, do not remove it. Cut it in such a way that it is still a little longer than the actual fill valve. As I understood it, the tube is there so that a certain space remains which is not filled with gas. Gas can than expand from liquid to gas form in this space, preventing getting liquid gas into your system. The empty space should also help with shot consistency, as the gas expands in the mag and not in the nozzle or barrel.

Try to switch the bolt with your friend (the rest of the upper stays): Does your bolt work in his MWS? Does his bolt work in your MWS? Narrowing down the error ... Or do you really mean the upper outer body (the upper hull), as the z-parts is just that: an empty hull. But I don't see how this part would not work anymore.

Mine is stiff, but no so stiff that you can't adjust click per click. If I remember correctly, usually when the adjustment was too stiff, then usually something was done wrong during re-assembly. I access the through the magwell, my fingers are just long enough

This and: Be aware, that your FPS will also increase during the day when you go from 10°C to 20°C. Might have to switch to green gas later in the day or install NPAS (and adjust accordingly)

The missing cap has no function except to cover the hole. In real steel, that's the magazine tube holding the shells, here it is an empty tube. Shells should be easy to find. Shells function as a magazine here. Check if the gas tank is not leaking, should be in the grip.

KJW are TM clones, so TM fit in KJW. KJW fit in TM but due to tolerances is a tight fit and might have trouble removing the mag. WE has its own design, not TM compatible. Other brands I can't tell. NOT 100% sure, but 95% sure on this: ASG uses KJW as a base, so TM clone Armourer Works uses WE as a base

Project definitely on hold. Managed to control my clickeritis (clicking on anything "add to basket" which I like) and just the bare minimum I noticed it would be much cheaper buying a new MWS than just building a new upper. I keep you updated when clickeritis has kicked in again.