Call it an exchange, you are buying something else. ;)
Finding parts for the CA is easy, check the PDI webs store (x-fire.org), everything you need is there.
The Well is unusable stock. Your stock MP5k probably has better range and accuracy. If you really want to upgrade a VSR, start from a good base, a TM VSR 10 is the best, but a JG Bar-10 could be an acceptable base too, it's is way way way better than the Well.
Also, a bipod is not that useful, it just adds weight to your rifle most of the time. A scope is nice to have, but the scopes they ship with Well VSRs are horrible. You can pick up a way better scope for 50$ on Deal Extreme. Or even better, get the real thing, like a Bushnell hunting scope.
Keep quiet. Sound travels faster than BBs.
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