I have seen weight changes everywhere from 6 lbs to 20 lbs.
All depends on how much of the F.G. filling and finishing was done before the first weigh and how much paint and primer was applied. Two stage systems can tend to add a bit more than is possible with single stage. Particularly if a lot of clear is use (as is sometimes the case).
I would say that 8 - 10 pounds is probably typical.
