About chokes
One thing that really should be done with a new gun is patterning.
Patterning is a boring but informative procedure that will give you very useful info about your gun, your choice of choke and your loads.
A standard rule of thumb about chokes (from the NRA Firearms Factbook) is that a shot pattern fired from a full choked gun will open at the rate of one inch a yard regardless of what gauge is used. A fully open or cylinder choke will open at two inches a yard. The other two common chokes Improved Cylinder (IC) and Modified (M) are steps between.
BUT.....these are rules of thumb and a particular gun and a particular load may be startlingly different, either looser or tighter.
How to pattern a shotgun requires a lengthy description. Google is your friend.
Basically, you get some butcher paper and make a number of targets 40 inches wide....draw a big 40 inch circle on each. Place it 40 yards away. Decide on your choke and load. Sit at a bench. Shoot one shot at a target. Put up another. Do it again. Do it five times (I only do it twice). Then you sit and count how many holes are in the circle. And in a smaller 30 inch circle that you draw inside the larger one; then you take percentages (you need to know how much shot was in your shotshell....there are charts for this.)
And so on....
Patterning will tell you how effective a given load will be between you and 40 yards. It will also tell you about where your gun is shooting relative to where you are pointing it. High? How high?
Pete
.
