I've used the cardboard box method and it will work. I only sight out to 25 yards. The whole idea is to get you on paper. Actually if its a good scope and you mount it correctly they will normally be on paper at 25 yards. They might be in a corner or something, but they are on paper.

I also use a RED DOT on two of my rifles. They are a nice sighting device, but I do not recommend them for long range shooting. 100 yards is about as far as I would trust one. 50 yards and closer, they are deadly. I like them in the woods especially at dusk or low light. The shots are close and the dot sure makes placing the shot easier. I think a peep sight with a ghost ring and a good broght fiber optic front sight would also work as well or better for you. Especially if some of the shots were long distance.

Some of the draw backs of them is the dot needs to change intensity, so make sure your RED DOT has intensity settings. My Bushnell Trophy has 11 settings. Bright sun is about a 8 dusk is about a 3. Also be careful of the size of the dot. Also under certain light conditions, the dot can grow a tail, like a half moon. You have to learn to ignore the tail and concentrate on the main part of the dot. I like a 3 MOA. This is supposed to put all your shots in a three inch circle at 100 yards, but from all my shooting, that's a pipe dream. Whether the larger groups are fliers, or you have the RED DOT moved off the edge of the bull which would then expand you POI. Who knows. For the most part I can hold them in there, but a RED DOT is not a guarantee. Another draw back is carry a spare battery with you. They tend to go out at the strangest time. The barrey does last a long time though. One of the red dots has been in for over a year and still seems to be going strong. The last thing is the viewing optics through the dot can be bad. It is almost like it makes your sight darker then normal, but then you are looking through a very small sighting tube which I am sure is the cause of that.

RED DOTS are great if your in low light, and close shots.