What’s the twist rate on the slug .22 23.5” LW barrel?

Please do your homework. Diabolo pellets are designed to stabilize via drag..
I did my homework for 40 years, working exclusively on the aerodynamics and ballistics of gun launched projectiles. Pellets are flare stabilized as stability is all about moments, not forces, and the drag from the flare base gives no stabilizing moment about the CG due to acting directly through the CG with no moment arm. The flare produces lateral forces when the pellet is yawed with long moment arms about the CG, thus giving large stabilizing moments. It is all basic projectile aerodynamics.