I just can't really justify using this card. Anyone else see some use for it? Even as a boss killer it stinks with only two ammo. Needed at least three if not four to be in line with the other 4 XP cards.

My main problem with the Shotgun is that it's a two handed weapon.  Roland needs his second hand for either a Flashlight or Magnifying Lens unless he has backup help for investigation.  Just relying on his card ability seems too slow especially if Cover Up gets drawn.  Maybe for a different Guardian it will be easier to utilize.  Preferably a Guardian primary with Rogue secondary since the combo of Shotgun + Extra Ammo is so expensive.

I can see how this seems too expensive both in experience and resource cost, but right now what other single card options do Guardians have to burst damage up for the beefier enemies?  Not many that I can recall.  Dynamite Blast is the only other single source if big damage and it can be tricky to use (especially in a higher player count game).  Other options are combos of 2+ cards like Vicious Blow + a weapon in hand or firing twice with a handgun which runs into the same issue of limited ammo.  I suspect as the Guardian's options grow using Shotgun with Extra Ammo as a boss killer will fall out of favor for some more optimal routes. 

That said Roland's big problem for me so far is not that he has issues killing monsters.  He's a pretty impressive monster killer even without a Shotgun.  It's that he goes insane relatively easily.  So If I need to bolster his weaknesses I don't want Shotgun.  I want an Elder Sign or something like that.

A monster can't drive you crazy if it's been turned into hamburger.

I agree but Treacheries certainly do a number on Roland for me with his relatively bad Willpower and low Sanity. It was rarely monsters that drove him insane.  He has a talent for pulling things like Rotting Remains from the encounter deck for me it seems.  My first game he went into the Attic and lost sanity and hit Rotting Remains twice.  The second time I had Guts in hand to play, but he hit a tentacle from the Chaos bag and that was it.  Wendy was forced to take on the Ghouls herself (Which she did.  I was surprised just how effective Wendy can be).