I am going to get a P-99, but I don't understand the differences in the trigger pulls. Is the quick action a consistent heavy or light trigger pull. Can someone explain the different models. Thanks

DNS,
Go to Walther-USA.  There is info about your question.  Some neat things to find there.  I just purchased a P99.  It will just take a nice day at the range to get familiar with the trigger.  Double action is a long and smooth pull.  Quite light though.  The single action is a long take-up pull then a nice crisp let-off.  It is very much like a two stage trigger.  The fit in the hand is perfect.

www.walther-usa.com
You are lucky that I picked up a Walther Catalog.
Here are the trigger weights for the different models and their operation.

P99- DA trigger pull is 10 lbs.
    SA trigger pull is 5.5 lbs.

P99QA- Basically it is a Glock trigger system with a decocker on it. Trigger pull is set at 5.5 lbs.

P99DAO- A 10 lbs Double Action only trigger pull.

Those are the stats.  However, the double action pull is quite nice.  Though long it is very smooth and does not seem to stack much.  I like it.

Just picked up my QA but have not been to the range yet.  I like the idea of the same trigger pull first to last shot.