Re: Reverse Missiles / not an "attack"
 

Uh uh. Beyond 1/2 Max. That's not necessarily the same as 1/2D range.

Re: Reverse Missiles / not an "attack"
 

Sure, but determining the kinetic energy requires diving into "The Deadly Spring." Now, you can get a fairly rough idea just by taking the RAW damage and applying the cinematic scale from that article in reverse to determine KE, then apply your equation (with the default 0.1 lb arrows GURPS assumes; I don't think your M value would be necessary, here) to figure out velocity, but I'm not sure it would really be worth the work. Much as Tactical Shooting basically just goes with, IIRC, Move 300 for handgun bullets and Move 600 for rifle bullets, just using the same velocity for all arrows may be the easiest way to handle things.

Re: Reverse Missiles / not an "attack"
 

The problem is in balancing everyone's needs. It's already a 240 page book, and the degree to which all GURPS fantasy players love it can be measured in all the books spelling out alternate treatments of magic, from Thaumatology to Religion to the Dungeon Fantasy line. Would people love it more if it were 350 pages instead? Or be all that less likely to bother with it?

The unfortunate problem is that you can't include every spell, and you can't put enough info into every spell to satisfy everyone, and you sure can't write any spell to make it idiot- or argument-proof. At some point, we just need to rely on our judgment as GMs to make rulings that make sense to us. If the subject came up in my own campaign, I'd do exactly that. The only reason I started this thread was to find out if there was an official answer I could take back to that Reddit topic, but I'd be entirely comfortable with doing things my own way regardless.

Re: Reverse Missiles / not an "attack"
 

No, that's just basic math -- it's equal to the area under the draw weight curve, which will be equal to draw weight * draw length * K", where K is a constant that depends on the design of the bow and is generally going to range between 0.5 and 0.8.

The Deadly Spring suffers from "too much math for a simple approximation, too little math to actually get it right".

Re: Reverse Missiles / not an "attack"
 

And what, pray tell, is the draw weight, draw length, and K-value for a GURPS Regular Bow at ST 11? ST 12? ST 20? I'm talking about determining the velocity of a GURPS bow, not a real one that you have in your hands or have the specifications for.

Just for the heck of it, however, here's what the velocity values look like, using my prior suggestion (determine KE assuming the damage of each bow is on the cinematic scale in "The Deadly Spring," assume 0.1 lb arrows - the GURPS default - and work out velocity from there). This looks at everything from an ST 7/8 shortbow to an ST 29/30 reflex bow; note the damage value is before accounting for things like Fine arrows.

I doubt anyone would want to bother with looking at that at the table, but there you go.

Re: Reverse Missiles / not an "attack"
 

It won't match real world bows because archers use heavier arrows for stronger bows.

Re: Reverse Missiles / not an "attack"
 

Real-world answer: arrow velocity will be 50-70 yards per second; the more powerful bow is just heavier and has a heavier arrow. The max speeds shown there are pretty much impossible even with a modern bow, let alone an ancient bow.