Correction: Wallyworld did have a few boxes of Winchester .410 3 inch shells loaded with 3- 000 buckshot pellets in stock, but my wife keeps some .410 slugs on hand for repelling boarders.
The little .410 doesn't get much respect as a defensive weapon, but IMHO an 88 grain .410 slug at 1800 fps muzzle velocity would probably ruin a BG's entire day. Or night, as the case may be.
If you're limited to 2.5 inch shells, Winchester has an excellent load (XB41000)which uses three 000 Buckshot. My wife handles it easily and it seems very adequate for "homeland security" in our Winchester 9410. They are available from most of the internet sales operations. I've bought them from Natchez.
Also keep in mind that at short ranges, even birdshot, by not having had much room to expand it's shot swarm is very dense, and will pack a much bigger punch than most people realize. Also, while devastating at close range, birdshot loads will minimize the hazard of overpenetration.