If you've ever dealt with 40mm shells. And all the ball bearings.
Not to mention getting them back together.
It has been known that CBSA inspectors will usually unscrew the two halves on the shells to "inspect" for explosives. Resulting in lost ball bearings and/or a useless shell. If you ever have shells arrive with loose bearings in the box, you can only imagine this is the reason.
The king arms shells come in a set of three for around $100. (check airsoftparts.ca)
I've found the KA shells seem to dismantle themselves while in storage. When you go back to use them after a while, all you can hear is bearings rolling around inside the shell :/
The KA ones are the only shells I have manged to reset numerous times. But even after a few weeks, they stopped holding a charge.
After buying two CA shells, they fired and reset maybe three times. The CA ones are easier to put back together because they have a special locking technique so no balancing ball bearings required. But I still can't get them to hold a seal, I think the o-rings shrink.
In all honesty 40mm shells seem cool from the front end, but after spending over 200-300 and only having two shells that "slightly" work. And the others are all in pieces.
If your really set on getting them, talk to Jugglez @ airsoftparts.ca
Anyone have any experience with the Madbull shells?