Whether they knock down the door depends on a) whether you are home when they serve the warrant, and b) if you are home, whether you try to climb out the bathroom window when they knock. They love knocking down shit and coming in hot.

If (a), then they'll pick the door or knock apart the bolt, but not knock the door down.
If (b), then your door is going to be headed for the floor real soon.

As for the underlying question; yes, a pound of MJ is enough for most cops to get a warrant. Whether they can and whether it is valid or not will depend on how much they know and how they know it.

My best advice to anyone with enough money to get a pound would be: 1) If it really is just for you, break it up and put it in different locations. 2) If you're selling, invest in getting a lawyer on retainer. You'll need one at some point.