If there was a "knight killer" crossbow, it probably would be something like this:

https://www.youtube.com/watch?v=MMoL_SBD6gw

Even then, it's questionable that it could punch through a breastplate:

https://www.youtube.com/watch?v=XMT6hjwY8NQ

Anything less than a single heavy plate though would probably be swiss cheese.

Lever cocked crossbow:

https://www.youtube.com/watch?v=M0m5udFoPnA

In GURPS plain plate armor is DR 8 but you can layer armor like quilt to get an additional DR 1 or 2. The Knight Killer does 3d6 impaling so the odds are good that a hit will be ineffectual or deal insignificant damage to a plate armored foe. Even with the 2x damage impaling does after the armor is penetrated.

Which is why you probably should try to aim for a different hit location than the torso. The +4 accuracy gives options. I had PCs shoot for the legs for example. Ultimately the key is to have the whole patrol armed and ready to shoot a volley.

Unrelated to knight killers are bows in Adventures in Middle Earth. Because of the low fantasy magic one of the keys to effective combat is to have everybody equipped with at least a short bow. I had two groups out of three adopt this within a handful of sessions as helped them with the opening rounds of combat. Compared to the usual setup where you may have an archer or two.

Opponents dodging is the real reason crossbows are suboptimal in GURPS.  Four rounds to load, one to aim, one to fire, and whiff, they dodged it.  It's a big investment in something that's not a sure thing.  Again, heavily armoured targets largely mitigate this because they've traded off move for damage resistance.

The Scout with Heroic Archer from Dungeon Fantasy can fire every second but is far more effective standing off, aiming and putting out eyes.

However I don't run my campaigns at the 250 pt Dungeon Fantasy level instead at the 125 pt heroic level. Scouts with Heroic Archer are not part of my campaigns.

As for dodging, yes that is a factor which is why it works best with the entire patrol shooting. I am not sure how many times I have to repeat that is it is situational tactics. Even the D&D version is situational.

Quote from: estar;1105874Here is my take on crossbows in D&D. The video is consistent with I learned and experienced. The one thing they didn't talk about is that crossbow came in different size and pose ranges even in medieval times. The knight killer below is based on the heaviest man portable crossbow that was recorded..

What is the estimated draw strength on each?

The crossbows we made in woodshop class in High school have a draw strength of 120 lb. I still have mine. That I can draw by hand with some effort.

Quote from: Omega;1106059What is the estimated draw strength on each?

The crossbows we made in woodshop class in High school have a draw strength of 120 lb. I still have mine. That I can draw by hand with some effort.

160 lb draw weight longbow vs 860 lb draw weight crossbow. The longbow arrows penetrated deeper into the target. In the video comments Todd says he expects the longbow would have superior performance vs the breastplate from the prior video.

I thought religious discussions were not supposed to be on this board?  

I'll see myself out.