With that short barrel on that pistol I wouldn't hesitate to go down to even 70 grs. You also didn't state it you were using a scope or not. My Accura doesn't shoot the 240 bullets very well butlikes the 300 gr XTPs
Another thing I've found shooting a pistol off bags is that they are sometimes pretty picky how they are laid across the bag. And you grip and trigger finger placement is also critical and must be consistent.