for those of you that try out on a pattern plate or paper, what size paper do you use and at what sort of range?

thought i would have a go and see what's what with different loads etc

Any size paper you want. But I use a square sheet that's 40" on a side, because that's the width of my automotive masking paper.
Draw a 30" diameter circle in the center of the paper. Then draw a cross in the circle to divide it into quarters. Step back 40 yards and aim for the center. Count the holes inside the circle. Divide that by the number of pellets in whatever amount of your shot charge. That will yield a percentage.

As he said, 40X40 minimum is the best. You can use smaller 36x36 if you are patterning close (inside 30 yards), but it is easier to use 40x40 min. Why, because you need to be able to capture the majority of the pellets to allow you to easily identify the center 30" portion. After you shoot a few, particularly if you are patterning at 40 or more yards, you will be glad you used the larger paper. Also, if you are going to take the time and effort to do this you may as well do it right so you will have confidence in your findings.

Another point, you do not want to draw the 30" circle until after you have shot the pattern. So, after the shot draw a 30" circle to capture the most pellet strikes. Why, because you are evaluating the load/choke not your ability to center the shot in a pre-draw circle on the paper. You can put an aiming point in the center of paper if you like but you don't really need it.

And, shotguns are not exacting insturments. They don't always shoot to the same point-of-impact (POI) each and every shot. Of course, you need to check you gun for POI, but that is another exercise.

Don't forget, you will need to shoot a minimum of 3 patterns (5 is better) for each choke/load/distance you want to know about. Lots of work? Yeah, if you don't like this sort of thing it is a bit teadious but it is the ONLY way to know what you load/choke is doing.

One more point to remember. You don't have to shoot all patterns at 40 yards. 40 yards is the standard for evaluating your choke's performance. It also happens to be a good distance to test a decoying duck or phesant load, but if you are looking for a good 30 yard load/choke for your quail gun or a 50 yard choke/load for your goose shooting then try you load/choke at those distances. Basically, try your combo at the distance you shoot your game/targets.

Good luck.