Its a great idea. I've done it before in wheat that the herbicide got away from us on. In grass it may be done, but there usually are quite a few "doubles" in the return. Doubles are basicly the same as a broken off wheat head tip where you have maybe 2 or 3 seeds still in the hull needing to be threshed a little more. The density wieght of grass will vary greatly, but an idea is that a 1680 factory hopper with NO extensions other than the factory fold ups will carry about 2.5 ton when full. Again it varies a lot and can be heavier or lighter depending on those variables.