When im around the green and try to use a wedge for anything less than i full ish swing i always either thick it or thing it, and i dont know why.
In my practice swings i do everything right, get the nice crisp noise as i brush the grass.

but on my proper go i mess up.

Probably the age old mistake of peeking early with your head to see where the balls going, thus you come up on the chip or pitch and thin the ball. Possibly also the subconsious part of the brain trying to help the ball into the air by making you do a scooping action.

The lifting of the head is something I used to do terrible on short shots. I now actually pick a spot about an inch in front of the ball and focus on that. I then try to make sure I swing to hit this spot. Therefore the ball which is between that spot and the club will be struck and hopefully with the correct desending contact.

cheers Christopher.
thats the thing practice shot fine real shot poor

If you are trying to hit a wedge shot less than full, which in my case is everything below 100yds then it is easy to fall into the trap of slowing down at impact as less distance is required, when in actual fact the way to play the shot is to choke down the shaft according to the distance required, trial and error is required for this, until you have it all in your head, and then play your normal tempo.

for fifty yds down to thirty yds I use the sand wedge, but apply the same principles.

They say that it is because there is no ball present on a practice swing. when a ball is there, we try to hit at the ball instead of swinging through, like we did on the practice swing.

Biggest change to my wedge play has been one simple though - keep your hands ahead of the ball. From being my nemesis to becoming stringth in my game. I now just need one simple thought for my putting that isn't "sh*t, I'm going to miss this one, and the one coming back"!

Like Danny mentions that can also be a factor, pratice swings are just that swings, but over the ball you try to hit it. One thing you can do to change this is go to a chipping green and hit chips or pitches where you don't even look at the ball but the target. Make a few practice swings this way then step into the ball and make the same swing but making sure you only look toward the target. You'll find you hit the ball pretty well.