TargetTalk

You are not allowed to make a grip with pieces aiding the hand to stay on the grip (free pistol being the extreme where the hand is completely surrounded by material). So no hand rest, thumb hole, material between the fingers where they cant rest, thumb shelf etc. But there are still things to improve like making a part thicker another slimmer or taking away a bump which doesn't fit your hand. The result has to have a smooth and flat surface, similar to the stock grip where you have to use hand strength to stay on the grip.
But like previous stated, the rule isn't perfectly clear so be careful that the result can not be interpreted as an "anatomically" fitted grip.

EJ wrote:You are not allowed to make a grip with pieces aiding the hand to stay on the grip (free pistol being the extreme where the hand is completely surrounded by material). So no hand rest, thumb hole, material between the fingers where they cant rest, thumb shelf etc. But there are still things to improve like making a part thicker another slimmer or taking away a bump which doesn't fit your hand. The result has to have a smooth and flat surface, similar to the stock grip where you have to use hand strength to stay on the grip.
But like previous stated, the rule isn't perfectly clear so be careful that the result can not be interpreted as an "anatomically" fitted grip.

Like mentioned previously that only applies to air rifle. You can do what you want to the prone grip.

Rob.