Which shotgun ammo would be best for blowing a heavy metal lock off of a metal door ?

12 gauge Disintegrater. Not sure why you need it though.

http://www.hi-vel.com/Catalog__24/Specialized_Shot...

Heavy Metal Shotgun Shells

There are a few different maker of what is commonly called a "Door Breacher" round. It's nothing more than a shotshell loaded with iron dust as a projectile. The dust acts like a solid projectile coming out of the barrel at short range (inches) and once makes contact with it's intended target makes a metal cloud that will do little damage to any one or thing on the other side of the door.

You do not want to use it with the barrel right on the target, but slightly way as the muzzle blast will tend to kick the shotgun back.

LAPD SWAT used a 1oz foster style slug for years as their door breaching round, but the "Door Breacher" rounds are better suited for the job.

If you have seen the old Master lock commercials where a guy blasts a hole through a padlock with something like a .308 or .30-06, it will give you some idea what you need. A shotgun projectile like a cluster of birdshot or a Foster rifled slug witl just mash flat upon impact. I have had to break open cylinder locks many times (I used to work on vending machines) that have the meanest and toughest steel you can imagine. They will burn up a carbide tipped masonry bit without any problem at all. You would need a high pwered rifle with at least .30-06 power and armor piercing bullets--and aimed at the shackle to break a lock like that open.

Use a short barrel with a cylinder bore and buckshot. Shoot the hasp, not the lock.

Hell, I'm just guessing.

18-inch barrel with muzzle brake firing door breaching rounds.

I saw that on mythbusters to. You cant, its just hollywood fooling your mind. The only thing you can do is nock the hinges of a door that arn't some heavy ****, like vault doors.

Try checking out these web sites:

http://www.firequest.com/G12-049.html

http://www.gunbroker.com/Auction/ViewItem.aspx?Ite...

http://www.cqbsupply.com/doorbreaching.html

http://www.securityprousa.com/dobr12ga.html

http://www.cheaperthandirt.net/AMM835-5.html

Short barrel...

They did this on Mythbusters and all guns were surprisingly ineffective inc 12 bore shot. It's a movie trick.