Re: Dealing with high DR
 

No need to make the DR lower or the horrible crap that is ablative. Laser weapons have at least an Armor Divisor of 3, and that brings effective DR down to 35. Should power armor be immune to dinky little guns that have barely been maintained for 200 years? Absolutely. Should lasers and blasters be a threat to the meat in a can? Also yes.

Get used to looking at the Armor Divisor on your weapons. The reason DR gets so high is that weapons develop higher AD instead of constantly going for more dice of damage. This also lets you shoot the guy without armor, and not create a fine, red mist or turn them into a pile of ash.

Re: Dealing with high DR
 

From the background you've described, them being functionally immune to small arms fire doesn't really seem too out-there - the OpFor will have to switch to heavier weapons to reliably get through.

That said, the power armor in the books is appropriate for a brand-new suit, not one that's been repaired and rebuilt from scavenged parts. The armor panels of the latter suit may give incomplete coverage (allowing foes to take a penalty to hit unarmored sections, or even allowing for random armor-ignoring hits) or be made of poorer materials (for reduced DR). You could also make them semi-ablative against burn damage, so that foes with lasers can eventually melt through the armor and hit the character.

One thing that may be causing a disconnect is that very few games use the GURPS DR model, simply because "No, your weapon can't hurt him, sucks to be you" is rarely all that fun in a computer game (in a tabletop game, you can figure out other ways to defeat/escape from the foe). At least for Fallout 3 and later (can't speak to the older games), armor gives something more akin to IT:DR - it serves to reduce damage by division rather than subtraction.

Re: Dealing with high DR
 

Fallout and Fallout2 used the GURPS DR model for Damage Threshold, which was subtracted from damage. Fallout's DR was the percentage reduction after the damage threshold (GURPS 4e IT:DR). The AC bonus was like GURPS 3e PD. In Fallout 1 or 2 power armor, you could engage in fisticuffs with an entire village armed with hunting rifles and pistols and not be harmed except on some lucky critical hits that multiplied damage (and then only harmed by a few HP).

Re: Dealing with high DR
 

As others have said: Armor divisors are the key.

Basically at higher TLs the toughness of materials raises to such a degree that you need to use proper penetrations. Armor divisors have the added benefit of causing less one shot kills that raising the base damage has.

Basically if you want to penetrate 105 DR 50% of the time will ball ammo you would need 30d damage, say 6d*5. The problem is that on a roll of 27 of the 6d (almost 10% of that or higher) you take 30 points damage after armor and on a roll of 30(almost 2% of time that or higher) you take 45...

But if you use a armor divisor the required damage is less. As example using a small shaped charge, a 3d(10) has the same 50% possibility of penetrating, but even on high damage rolls you single hits do not cause multiple death rolls though armor. The same to a lesser degree with lower divisors. Further when using firearms with AP ammo the injury modifier is lower, further limiting the maximum damage.

Re: Dealing with high DR
 

Power armor needs power.

How about attacking it with EMP-based weapons (or ion weapons or whatever it is called in your setting).

Re: Dealing with high DR
 

Outside of nuclear explosions, EMP's are pretty rare in Fallout, and aren't as effective as they are in our world (as Fallout uses vacuum tubes and the like, having deviated from a normal TL progression somewhere in the 50's). Seeing as they were presumably designed for nuclear warfare, I'd expect any power armors that would normally be susceptible would have proper EMP shielding.