The CA249 mechbox is more or less a solid block of metal. It's like 90% metal and 10% space for your internals
. Seriously though, it accounts for like 1/5th of the weight of the CA249, and given that the CA249 is itself a massive piece of metal, thats saying something.
Anyways the CA249 box isn't going to break anytime soon. However, its hard to say if its due to the sheer thickness of the thing or due to the design (I'm inclined to go with the former). Having said that, the Star M249 mechbox is plastic (and clear plastic at that
) and may be plauged with all the structural issues of your regular V2 mechbox.
Oh, and regardless of which 249 you choose, make sure you can fit a full sized 9.6v battery in there. If your a SAW, your gun will see plenty of trigger time. Having a high ROF won't hurt either.
Upgrade those gears too. I didn't bother with heavy spring upgrades. Generally, with a fast firing weapon, you'll want to focus on efficiency and air compression rather than high power.