I'm having a lot of trouble with these hack squats - the bar wants to catch the back of my calves going up, and then bang my achilles heels going down (made the tendons really sore when I got to a heavy weight). I'm getting into all kinds of bad form trying to keep the bar from contacting my legs. Is this a common problem? I have gotten pretty damn frustrated with this exercise!

Barbell curl - how stationary can you stand while curling a lot of weight? This may be a stupid question. I'm up to 150, which is a little less than 3/4 of what I weigh. I feel like I've got enough power in my arms to curl it, but I can't do it without swaying back. I think this is probably bad form, but, "for every action there is an equal and opposite reaction," so, on the first part of the movement, when you're pushing the weight away from you're body, wouldn't that inevitably tend to push your body back in the other direction? It's not a movement where you're braced against anything, like the bench press.

I'm rambling on now about a simple question - is sway bad, and if so, how do you avoid it?