When do your players can announce that they will be using Bolter-Drill (RoF +1), before or after they make a BS test?

Kain McDogal said:

I make them declare it beforehand. It makes Bolter Drill a much better Talent for, say, Bolters than the Heavy Bolter, but it just seems that it's more fitting if used that way. It seems somewhat odd to be able to fire a burst, then decide to squeeze out one more shot since your target didn't go down and your shots were accurate.

Before. It would be bizarre to pull the trigger a few times and then decide that you actually pulled it faster than you did.

INterestingly while before it was better for bolters than heavy bolters, with the optional weapon rules it has now probably reversed. Now both weapons need 6 DoS to take advantage of it (rather than 4 for bolters and 10 for Heavy Bolters) and it is easier for the HB to get more bonuses to increase the chance of getting those DoS (full auto, longer range, Devastator almost certainly going to have BS as high as he can etc).