New BAA impression taking guidelines.

Here

Personally I'm not keen on the bracing hand position used in the gun technique as it won't prevent the tip being pushed forward if the trigger 'jogs' on the ratchet mechanism. The problem is that the bracing hand sits against the fist of the trigger hand - exacerbating the issue while not preventing the force from the palm of the trigger hand pushing the gun forward as the unloaded/skipping trigger collapses backwards.

I can't see why clamping the actual nozzle between thumb and forefinger while using either the back or front of the hand and remaining fingers to support and steer the nozzle isn't preferable.