This is for a hunting rifle in .458 SOCOM. Shortest legal length in my location is 17.5".

Barrel blank will be a 1:14" Douglas .458 from Brownells.

Any comments? Too light? Too heavy?

could always buy an off the shelf 16 inch and pin the flash hider to make your length?

There are no .458 SOCOM barrels to find in the US. Finding one in Sweden is more or less totally impossible.
But I have good availibility to .458 blanks and a good gunsmith that can do the barrel work.

The questions that remain for the profile sketched above:

1. 18" is pretty long. Would it hurt to not have it threaded for muzzle device? (I do not want a 16" with pinned device)
2. Is the length of the taper on the OD of the chamber area enough?
3. Would a longer taper of the .980 to .750 be more beneficial in terms of less risk for stress cracking of the material?

My socom barrel was very similar.  I don't think it had a taper, but I think the dimensions were almost identical.

Made for a handy gun.

TROMIX has 16" lightweight barrels with the same barrel taper as your original post just go to http://www.tromix.com/458-socom-parts-1.html. I recognize that isn't the length you're looking for but I was just saying the barrel weight isn't too lightweight. also I am not sure what length gas system your barrel is but try to make sure its a carbine length system. I hope your gunsmith has the ability to obtain the true chamber dimensions from marty(teppo jutsu) as there have been a lot of QC complaints with the reverse engineered barrels out there. Also about having the barrel threaded for a muzzle device, I personally run my socom with just a thread protector, the rifle does not kick hard at all so a brake isn't needed. If possible I would have got mine wouthout a threaded barrel. for a plethora of information I would join the 458socomforums.com and also try to get in contact with Tony Rumore

How do Swedish regulations treat flash hiders and muzzle brakes?  Do they consider a blind pin and weld or silver solder as a barrel extension?  

Regarding shooting with no flash hider at all, it's no that bad.  I imagine the burn time for the powder in an 18 inch barrel should be generous, and flash shouldn't be excessive.