Durabilty of interior doors...

None are going to even slow down anything from 9mm up. Nothing short of a purpose built bullet resistant door is going to give you any cover from gunfire.

As far as resistance to breakage. Both solid core wood veneer and steel cased doors reted for exterior use are going to be very good in this regard. The real weakness is the connection between the door and the frame/wall behind the frame. You must use something other than the issued screws for the hinges and striker plates (the brass part that is screwed to the frame the lock plunger or dead bolt go into).

Use 3" long "Deck Screws" to secure the hinges to the frame and the striker plates to the frame. These screws will extend into the 2X4 wall studs and make kicking open the door very difficult.

On an interior door you will want something besides the standard knob. You will want to install a dead bolt also. You may also want to consider a blind dead bolt (the kind they have on rental property like apartments) that generally installs above the standard deadbolt and is only operable from one side.

I kick doors for a living. I am 6'06" 275# and generally have no difficulty gaining entry into a house (when legally required) with one good kick. If the door has been secured in the above fashion, it takes me 2 or 3 really hard kicks and I am larger than most people you have ever met or ever will meet.

 

All of my exterior metal doors have extra deep set dead-bolts, with cheap store bought steel striker plates, backed by two extra 2x4 set with ring tail nails and 6" screws, additionally I have screwed 1/4" metal plates to hold the jambs and striker plates to the entire assembly to make it real. This is all set in a 2x6 frame in a brick home. I'm 6' 2" 365, I think you would find yourself on your keister if you tried to kick one of these suckers down! I do agree that a normally constructed door frame/jamb is a joke and offers little or no real protection. As a former emergency response trainer I've been through a few doors myself.

 

Forget bullet penetration... unless you buy a door specifically designed for bullet stopping, you are SOL. And you won't find that at Lowe's... Besides that, your door frame is the weakest part of the door assembly. Unless you plan on building a fortress, just use a steel clad laminated exterior door, with a steel re-enforced frame, anchored with titanium lagbolts.

 

I can't see any reason why that wouldn't work... Don't forget to put a peep hole in it. You certainly don't want to open your door to a gun wheelding invader.

 

It's enough time though. There was a home invasion about 4 days ago, where 2 BG's kicked a front door open. Upon entry, the first BG met a 45ACP to the forehead and died instantly. The second BG was showered with 45's but he managed to somehow get away... The door was a solid hardwood door with a secured deadbolt. However long it took to open the door, was long enough for the owner to prepare for a fight. The perps were armed but never got a single shot off.

Robocop10mm knows what I'm talking about. Once the act of breaking in is in motion, all you can do is run or be ready. Some doors take a little longer than others but all doors are breachable.