The Engineer achievement Patent Protection is eluding me.
The achievement's description is:
Destroy an enemy Engineer's sentry gun with a sentry under control of your Wrangler.
I've destroyed mini-sentries and regular sentries currently being built with a wrangled Mini-Sentry, but still haven't gotten this achievement.
Are there any restrictions as to what type of sentry you're using, what type of sentry they have, and the enemy sentry's build status?