Preliminary comment this just to state that the GoodKarma archive GLoups just posted is the exact same one I'd be uploading for you, Cat, so you can begin experimenting with that one. I'll be checking out GLoups' Torlan GK demo later to see how far that gets us.
Lastly and regarding attributing frags, this has to do with the Instigator/instigatedBy variable, not DamTypes, which is info received during a TakeDamage call about the Pawn who last shot at (and/or imparted momentum to) the exploding/karma actor, being remembered/stored in order to be used during an Explode (with resultant HurtRadius) or Bump or EncroachOn call later on within the same class' code; stock DECO_ExplodingBarrel uses a DelayedDamageInstigatorController Actor variable for this, which is relayed to the Victim actor via a function reference. For more on that, one can review the stock exploding barrel's UScript code here.
Anything about UT2004 mapping, Uscripting & more