.12 gram BBs and Airsoft? Can it be done?

I am planning on buying the Tsd mp7 airsoft gun seeing as i need a gun for when i play medic. The tsd company re-shims and installs a metal hopup, however 235 fps with .20s is simply not enough. With .12s, it chronoed at about 330. If i use .12s, will it break this gun, and why? I would use the best seamless and polished .12s. Also is it possible to upgrade the mp7 with an m110 spring? Thanks.