Last couple of times I've checked with the following method using rifles that have a scope I dial with and a 100 yard 0:

1. Shoot 1 100 yard shot
2. Drive to 200 yards, dial for and shoot 1 200 yard shot
3. Drive to 300 yards, dial for and shoot 1 300 yard shot
Go check the target...but I can already tell from 300.

I shoot from a rest on the back of my four wheeler, in my driveway, and it's just a couple of minutes to do. I usually don't shoot my steel target from 100 yards but I've done it with these, it's just standard short action rounds, no mags. Quick and easy.

Here's my "bench":

[Linked Image]