A way to make blast charges much less OP.

[ApexPredator]

1) This is not an option. As long as charging blasters are in game, they do affect game balance. New players will be bored by how easy the defence is and will balme - and rightfuly so - the design. Or the game, more likely. If they game is balanced around defences with BC, their usage will become more or less obligatory.
2) This only nerfs outside bases while keeping undergrounds and funneling unchanged.
3) This does not address issue at hand in any way.
4) This is actually a resolution to the problem.
5) This is just an awful idea. It makes no sense whatsoever, it makes BC useless and heavily random in effect and is simply a bad design. It would need to be really heavily explained to the player, and if you need to do that for something so small, you've failed in your design. If it's not explained properly, players won't know what hit them and will blame - again, rightfuly so - the game. It's counter intuitive, unfair and punishing. It's simply really, really bad idea.

All in all #4 is the best of mentioned if you want to fix the BCs problem. #5 is best, if you want to get rid of BCs problem and half of your players at the same time.

To your responses:
1) Really? Not an option? I just proved it with my game play. My hand wasn’t shaking at all either when I was choosing what to research.
2) Are BC so important to your game that you will funnel raiders into your base just to use them?
3) In the amount of time it takes someone to go get metal and build a BC then clear the area and set it off I could have had one person mine out the equal amount if not more. There is no reason to use them to blast rock when they only take a few blocks. Maybe if there were some blocks that you could not mine then maybe.
4) Removal because the average user can’t control themselves is a sad “resolution”. Maybe remove the damage they do to col/raiders.
5) Clearly this was a joke.

[Trensicourt]

It could be a fix to make charging blasters destroy (not detonate) other charging blasters within a good radius - bigger than explosion itself. Of course to work it would need a way to make it impossible to detonate all mines at once to work around it - one way to do it would be manual detonation (through console or a detonator item). Another possibility would be to add a random (1-100 ticks) variation in fuse time. The later would nerf mine fields double as much - not only because of the initial mines destroying mines rule, but also by ensuring you don't know which mines will actually blow if you try to set them all alive at once.

The fuse variation is an easy fix to balance to BC. Also, HOW COULD YOU NOT DETONATE ON A RAIDER?? If you can't, make a barrier and force the raiders to break through the door while it is in range of the BC.

[Galileus]

1) The way you play your game is not a proof to anything else than that you play your game in a certain way. The fact one beat's the game is in no way a definitive proof of anything at all. You've also not touched on the argumentation I've provided.
2) It is still the same argument of balance. If there is a possibility of using funnels with mines, you have to account for it. If you ignore it, you'll teach your players one technique and you're stuck - because you can't provide anything different. If someone finds the funneling trick, he'll abuse it and fail on any challenge that does not work with this trick. And it is your fault, because you've failed to communicate to the player what option he does have.
If, on the other hand, you account for funneling trick in balancing of the game, you make it more or less obligatory to use them - because they are as powerful as they were, and so the challenge will be scaled so.
It could be indeed ignored, if we talked about some minor and hard to find strategy. It's not the case. Underground expansion at this point of development is a very natural way to go, and way too many players would find funeling/mines combo as the way RimWorld is supposed to be played.
3) The issue at hand is the way BCs are too powerful as a defensive tool. Changing it's balance as a mining tool does not address that issue.
4) A game element that requires players to make a conscious decision not to use it, because it makes the game too easy is a sad state of affairs. It's by no means a player's fault he uses the most effective tool at his disposal - after all, he paid for a product that is supposed to be well balanced and pose some kind of challenge. If player is forced to rebalance it by making up handicaps for himself, it means it's a shoddy product with a bad design.
5) With triple A titles design decisions, I wouldn't put anything past a random person on the interwebs. Nevertheless, you've successfully proven my lack of humor.

[divious]

Grenade/motolov and shotgun raiders come up close. Rifle raiders are in the middle and sniper raiders at the back. Mortar raiders all the way at the back. What about tunneling raiders.

On Randy Random I had 2 raider packs spawn in the space of a few minutes with each other. That did not allow me to replace my set of BC's which I specifically use to neutralise close range raiders, where when they are all gone I fall back to choke points and force the snipers to come in close, then I punch them to death.

Granted I haven't played as far as some of you, I would have the game expose more variants of the raiders before I would let the BC get reworked.

[Anemia]

As kind of a spin-off on Galileus thoughts I think that the blasting charges should be manual detonation with a timer (something like 5 seconds, so that you can time it for raiders and you also have a good amount of time to get away). In combination with having them destroy other BCs within their radius. I think that would keep them viable as base defence to take out a couple of raiders or if you have a several fall back positions with BCs. As for their "intended purpose" I think they should be left as they are and if we get some other mineral/rock type that takes a longer time to mine then they could be used for that. 

[Karakoran]

I like the idea of using blast charges as a last ditch effort to prevent raiders. It seems silly that a colony would fall because no one wanted to use them purely on rock. Possibly making them have longer fuses, being not particularly effective on walls and people, and making them better at mining would be nice. Also an alternative like mines would be great as people wouldn't need to or really want to use blast charges for fighting in the first place.