Each time a Stenguard Veteran squad fires, the contorlling player can choose which type of ammunition is being used.
Well, that's not really specific. Lets look at shooting.
2. Check range. If a target is beyond this maximum range, the shot misses automatically.
In order to carry out step 2 the range of the weapon must have been established. There is no permission to measure before that. The latest you could select ammo is between steps 1&2 (i.e. after choosing a target and checking
LOS).