I did read the FAQ on top.  I am new to shotguns also.

Anyways, my gun is a new Rem 870 18.5" w/ choke tubes.  What is a good self defense round that won't over penetrate?  I see that 1 buck is suggested but who makes a good 1 buck?  Do you want something that is hard plated or not?

If you want minimal penetration get some of the 'low recoil' rounds. My department did an evaluation of our duty rounds and our low base buckshot was the only thing that was unable to penetrate a vehicle door.

Federal Premium 00 buck with the flight control wad is great. Ive also heard some great things about the Hornady stuff.

Plated is much better than just lead balls. It gives a tighter pattern. But the plated stuff costs more, so I suggest getting enough for 3 mags full and getting what ever you can after that.

A rifled slug is a good thing to have too at the end of your magazine. It will silence the problem.

I still like 00 buck over #1 buck. Bigger balls deliver a much more massive wound channel instead of a lot of little balls spraying all over the place. 00 buck is also much much easier to find.

Get a box of a few different brands of plated 00 buck and a cheapo box of the 15 round value packs of Winchester 00 buck (slugs too if you want) at wal-mart. See which brand will have the tightest group at the longest distance in your house. Try to get all of the balls as close to the center of a paper plate that you can. Use a Modified choke, its an all around good HD choke

What door were you using? I was unable to achieve 1-sided penetration on a car door RELIABLY past 15 yards with anything but OOO Buck. This was an '85 crown-vic car door. I am sure newer fiberglass doors are not nearly such effective cover.

Okay okay, I have finally stopped convulsing with laughter enough to address that. In all the gel tests I have ever seen, OO penetrates 16-20+" while #1 tends towards 12-15". The #1 buck has also been proven to create far more tissue disruption as it has a larger surface area due to more pellets with only slightly smaller diameter.

Buy a variety of buckshot loads and usethe one that patterns the best in your shotgun.

Federal "flight control" or Hornady TAP are good places to start.

# 1 Buck (Rem or Win) and the plated # 4 buck from Fiocchi are my two fav home-D loads.