It is a BSA 30mm collimator with adjustable shotgun arbor. When I say the alignment changed it was 3 grid line lower horizontally but still dead on vertically. My guess the reason being that when the choke is removed the arbor goes in farther (deeper) because the barrel opening is larger than the tighter choke which make the collimantor a little higher. wow thats a mouth full! Does tha make sense?