Thrown prop_physics with "onworldimpact stick" behaves strangely

I made a sword, which is supposed to act like the harpoon from halflife 2 when thrown with the physgun (stick to the wall and pin NPCs)

Sometimes the sword sticks to the wall without even touching it and sometimes it disappears entirely into the wall. Also, it starts to spin soon after the launch, despite having the “spin_none”-parameter, and often sticks to the walls with a blunt side.
Any ideas what could be wrong?

Those were thrown from not more than 128 units away, one sword is “sticking to the air”

The .qc:

$modelname	"Sword.mdl"
$scale			8
$body mybody	"Sword.smd"
$surfaceprop	metal
$cdmaterials	"models\Sword"

$sequence idle	"Sword.smd"

$collisionmodel	"Sword.smd"
	$mass		100
	$concave	1

		base		metal.Medium
		allowstatic	1
		mass		100
		preferred_carryangles 	"0 90 0"
		onworldimpact 			stick
		onfirstimpact			impale
		onlaunch				spin_none