I have a FX400 22 caliber smooth twist and I shot some NSA slugs today. I knew they would not shoot as good as pellets but wanted to try and see how they would shoot. 35 yards. Not so good.
No mention of FPS, so the assumption is that you are shooting slugs and comparing groups with pellet tuning. Therein lies the possible determining factor.
This is an original smooth twist FX400 not the full rifled smooth twist. No slug liner. No tuning. I just wanted to see what would happen when I shot a slug vs a pellet.