Build sentry
Destroy
Get crits
loving OP as bullstuff
Sentry has to actually do kills before you get crits, hardly OP. And even if self destructing the engi's sentry does give crits, people who do this are morons, its only good if you need to fall back and rebuild a sentry or defending a point and you loose your sentry.
Its actually quite useful and it only holds 3 shots.