Comrade Dmitriy,
Accuracy is a term difficult to generalize....blah blah blah.
You must consider the distance in question. 2 meters or 7 meters or maybe 10 meters shooting range ? It is easy to make an accurate gun to say 3 meters shooting range but to go 10 meters and have pin point accuracy, it is not easy.
Since accuracy grouping expand or get worse as distance is further, a 1 inch accurate gun at 3 meters is good but 2" accurate at 7 meters is superb.......up to the hunter requirement and definition.
As long as a gun can place the shaft 'roughly" where u aim with enough penetration for your kind of hunting and stoned the fish, that's a good and accurate gun.
Also one must try enough guns to say that a specific one is accurate, you must have something to compare with or a reference grouping on a target sheet. Spearguns do not have an industry standard like fire arms or precision air guns where the common "accurate" standard is :
This is a 1.5" gun at 100 yards for 3 shots grouping (firearm ) or
This is a 0.13" gun at 10 yards for 5 shots group (airgun )
I never try a Beuchat, so I don't know if it is the best in accuracy but I once owned a Scubapro 85cm pneumatic and for 2 meter work ( that's all it is potent for, under 5kg fish ) I never tried anything this accurate ( it is consistently accurate ). I am comparing it to Mares Stern and Mares Cyrano, Picasso band gun, JBL band guns ....basically small guns category that I shoot within 2 meters of range. Also I shoot target board not only moving fish, thus I can say that I have done enough test to satisfy my curiousity.