Alternatives
Of course, buckshot is the optimum load for "welcoming" criminal aggressors.
However, if buckshot is prohibited, unavailable or simply too darn expensive,
I would recommend two fair 12ga substitutes:
Winchester Ranger 2 3/4" extended range HV shells loaded with 1 1/8oz of lead BB shot. This is made by Olin Corp Australia and so may be hard to get stateside. This round actually kicks harder than some magnum OO buckshot and at 11 yards, was able to shoot through 110 pages of paper covered with 3 t-shirts. I'd reckon that it should be able to penetrate 6"s into a BG's body. On average, I was able to get 13-17 of these .18" pellets into a 6 inch group centering around the heart area. I don't know about you, but 13-15 seperate holes perforating my heart, lungs and stomach is something I dread to think about.
Another round I have tested is Fiocchi's PL32 2 3/4" 1 1/8oz #4 birshot load. The kick on this one is quite manageble. At 11 yards, it was able to shoot though a hardcover highschool yearbook. Anecdotal evidence from other shooters claims that feral dogs can be killed with this load when shot from close range. Hence, if a 80lb mean dog can be dispatched by 1 shot, 2 quick successive shots to COM on a 160-170lb home invader should seriously ruin his day.
However, even if I have to load my HD boomstick with turkey or waterfowl loads, my backup plan involves a baseball bat. I figure that if the home invader has already taken a torso full of 1 or 2 shells of BB or #4 shot, he must be seriously hurtin' and I would have the advantage when trying to club him on the melon using my bat.