With respect, I think you are very wrong in your choice of the first shot.

Yes, birdshot may discourage a burglar or home invader, but it may not. Shot in the face or eye, perhaps, even probably, but you're talking about correcting for the second shot or even subsequent shots.

I think the first shot, if it needs to be fired at all, should be one that will probably stop if placed in the right spot. Remember, the burglar may be armed and firing, too.

Make the first one a round that will, if placed properly, end the affair.

Bob