Thursday is GURPS-Day, and I’m going to try and answer a question that +Jason Packer probably already answered for himself. But I write what hits me.
He noted in a post that there are ways to randomly hit lots of things in GURPS, but “chinks in armor” doesn’t seem like one of them. Are there any ways to hit the chinks or armor gaps in GURPS randomly?
I think formally, no. But practically, there might be one and one can squint the way to another.
The only RAW method might be that on a critical hit, it’s possible to roll a result that halves DR. That could easily be read as “you just hit the chinks in armor!” What that precludes is an actual defense – the only time this happens, it happens automatically, with your foe not able to parry, dodge, or block due to the crit.
The alternate might be to say something like “if you make your hit roll on a random location by X, then you hit armor gaps.” This X should be fairly large, since the basic penalty for armor chinks is -8 to -10, depending on what you hit. “Make it by 6-8” works for most locations, and since the penalty to hit a random location is 0, putting it as “make it by 8” is probably a decent way to go.
Edit: Chinks on the torso is -8; everywhere else is -10. “Make it by 10” and “score a critical hit” aren’t that different, so I don’t know if that’s a good option.
The best option to get this done easily is to grapple the guy (halving location penalties) and make a telegraphic attack, which brings you to -0 on the torso and -1 for everywhere else. Use a proper CC weapon. That doesn’t really address Jason’s original question (the random part of it), but it is a much higher percentage option for a difficult location. If you’re using Technical Grappling, you can skip the Telegraphic Attack and spend Control Points to lower the hit location penalty, too.