Matthias is right. And perhaps one of the foremost contributing factors in Engvall's triumph over Bray's record was the fact that more of his energy went into enhancing velocity as none need have been traded to achieving spin stabilization.
On a side note, I heard back from Guiness and the internet must have really pinched their market....as they seem to be a 'shadow' of their former selves and appear uninterested in our sport. That is unless one is willing to use all natural materials, ammo included.
Interestingly, their requirements say absolutely nothing about prevailing wind direction and speed for the attempt.....!
Ratio of mass density to drag profile is of paramount imoportance to achieving maximum distance, which is why I sometimes use 1/4" Tungsten rod for extreme distance exercise.
Also, regarding fin stabilized ammo (and perhaps even spheroid shapes employing the overhand cast)....an excellent way of adding velocity is to control the timing and release angle such that the dart is made to slide forward along an arcuate contributor mass at the moment of release.
Similar in principle to this example:
TS