Are sand bags that fit under the stock legal in HFT / FT? Obviously in HFT they can't make the fore end deeper than 150mm from c-b.
Any hamster type support has to be fixed to the rifle, you can't use anything loose on your knee, like a cushion, or sand bag. as you say, UKAHFT rules limit depths as well.
Gus
The ox is slow, but the earth is patient.