I have to admit that I'm getting annoyed by KJW regularly taking their calipers to TM's work. It's quite alot of effort getting all those parts to move in unison and fire a pellet reliably only to have your hard work getting ripped off.
Recent TM GBBs are on the pricey side for a plastic GBB, but you can really tell that some people really sweated over the design. Good material selections and parts which really fit together well indicate a degree of lifecycle testing and possibly second or third generation tooling. Usually, your first try at making injection moulds on a new product aren't quite perfect. You get poor fits here and there which can sometimes be fixed with a bit of mould rework. Sometimes you have to adjust your tool design and start all over again. To get really good part fits, you often have to do a few cycles of rework and possibly more than one generation of tooling. Crappy fitted parts indicates little rework and sometimes only a first stab at tooling.
My experience with KJW has not been especially positive. Far too many guns malfunctioning out of the box. Some glaring design errors like mistakes in spring design (in the KJW Para Ord) which are consitently repeated in every gun. It blows my mind that KJW still uses single port fill valves in their mags.
Take apart your KJW mag sometime and compare it against it's TM twin. You'll note a stubby tube about 1.5"-2" long in the TM mag base and a brass tube attached to the valve which goes inside the tube in the mag base. Conversely, your KJW won't have this difficult to justify collection of bits.
What most airsofters don't know is that the TM mag has a feature which ensures consistent magazine filling regardless of magazine or propellant tank temperature. TM mags sound leaky because they're double port valves. Depressing the fill stem opens two passages in the valve. Liquid propellant flows down the centre of the stem and gas is allowed to escape around the sides of the stem which gives TM, KSC, WA and many other Japanese mags a charactaristic leak and the liquid backspurt when the mag is full. This is not a defect. What the second port does is allow gas to leak out of the mag to prevent the pressure inside the mag from equalizing with the fill tank pressure. At some point the liquid level in the inverted mag reaches the tip of the stub tube in the mag base and flows up the tube instead of totally filling the mag with liquid. The liquid backspurts out the secondary port which indicates that the mag is full.
The bypass port assures that a measured quantity of liquid is transferred into the mag even if the mag is warmer than the fill tank (warmer = higher pressure). If you're doubtful, try this: warm up an empty mag with warm water (put it in a ziplock bag and dunk it in a sink of warm water). Toss your can of gas into the fridge. Allow 10 minutes to warm the mag and chill the tank and fill the mag. You'll find that you can get a decent fill of gas into the mag even though the tank is cold (low pressure) and the mag is warm (higher pressure).
Allow the mag to return to room temp for 1/2 hr and count off how many bbs you can shoot. Repeat the trial with the KJW mag. Ever wonder why a Japanese mag can often shoot off twice it's capacity in bbs while a KJW can sometimes barely fire off a full load of pellets?
The other thing that the stub tube does is assure that a minimum quantity of gas is allowed in the mag. GBBs do not operate well on unevaporated liquid propellant. If you fill a mag completely with liquid and allow no gas space, you end up with very poor performance which blasts liquid propellant mist. It's difficult to cause this with a TM GBB, but you can do this with a KJW mag. Throw the mag in the freezer for 15min and fill it with a room temp tank (do not intentionally warm propellant tanks). Hold the filling probe down for at least 10 seconds. Let the mag warm up to room temp for 1/2 hr and see how well your KJW gbb works. It is possible to overfill KJW mags if the mag is cold from alot of shooting and the tank is warm (say you left it in the sun).
It's absurd that KJW hasn't picked up on this simple valve issue. They've manufactured perhaps hundreds of thousands of GBBs and they still use the same crappy fill valve. It drives me to distraction when I think that the GB Tech gas grenade/reservoirs have the same junky single port valve. Neat looking gas reservoir disguised as a distraction device, but the thing has been made useless with the single port valve. I can't get more than 10g of propane into it without freezing the thing. A doublestack WA mag holds 8g of propane so you can see how crippled this product is.
Want nearly free GBB gas?