Why?
Butt hooks are not permitted on air rifles, there are specific ISSF regulations as to the max depth from bore line, curvature, etc. Look on the ISSF website for the full rules.
The only exception would be if you are shooting an air rifle prone in NSRA 25yd comps, but then a butt hook makes little diference prone and is not used by many prone shooters even though permitted.
Good Shooting
Robin
Walther KK500 Alutec expert special - Barnard .223 "wilde" in a Walther KK500 Alutec stock, mmm...tasty!! - Keppeler 6 mmBR with Walther grip and wood! I may be a Walther-phile?