I give it max 5 rounds before the front of the tripod dislodges from the window sill and either falls forward out the window or backward.

Assuming the window is not somehow fused into being one with gun.

Then I guess it would be around 5 rounds before also the window shatters?

Also the ladder would collide with the grips on the m2 for what seems like a lot of otherwise useable firing angles.