Gentry, congratulations on your purchase!
Apologies in advance if any of this covers ground you've already gone over. My belated two
Find a reputable professional instructor and reserve a weekend and a few hundred bucks.
Know your state's laws on the use of lethal force.
Understand your weapon's terminal ballistics (the effect the projectile has on the guy you want to make terminal). Also understand that if you have to use a firearm defensively, you will want to remove the threat by immediately incapacitating him. I suggest the writings of Dr. G.K. Roberts, who moderates the terminal ballistics forum on M4carbine.net
. Go read some of his sticky posts at the top of that forum, starting with Basic Wound Ballistic Terminal Performance Facts
. Then you will understand why I write the next two things:Never use birdshot as a defensive round.
It will not consistently penetrate enough tissue to produce incapacitation.Never rely on the sound of racking the slide as a deterrent.
The effect of this is highly dependent on your aggressor's mindset and may be more of a liability than an advantage. If you need a gun, the time for reasoned discourse and persuasion has passed.
Don't screw around with less-lethal rounds. They are not intended for your situation (as described and implied thus far). They are intended for use by cops who have the equipment and training to restrain a suspect after he's temporarily subdued - and who have backup with lethal firearms on scene and ready to engage if necessary.
Birdshot is fine for practice. You'll still learn how to manipulate the weapon and - this is a subjective observation - its recoil is less fatiguing over a range session or class of a few hundred rounds. For defensive use, do a bunch of research and make your own decision. The general opinion in the tacticool forums in which I lurk seems to be that #4 and #00 buckshot are optimal for most civilian defensive use, while slugs are best reserved for the occasional longer shot or for turning cover into concealment.
Become comfortable with the weapon. Learn how to run it under stress (again, training) to minimize the chance of an operator-induced malfunction and to develop the muscle memory for manipulation when adrenaline turns your hands to flippers.
Understand that you still need to aim. The rule of thumb for buckshot's spread is 1" of pattern per 36" of range. In my house, my longest shot allowed by architecture is just over 30', which gives me a 10" pattern. That's some room for imprecise marksmanship but not a lot. Test your intended defensive load at your maximum likely engagement range so you know
how it patterns in your gun. I got a nasty surprise when I tried out Federal's FliteControl load and got a pattern at 40' that was only slightly larger than a single slug hit.
Have fun! Be safe! And if you can't be safe, be dangerous to the right people.