What kind of reflex?
Haven't seen a direct reflex to Contender mount, I think you'll have to go weaver/picatinny.
The basic Weaver mount covers just the 4 holes in the back.
But you may need a picatinny rail if your red dot has that mount.
Some pic' mounts work on weaver rails, some don't.
Look at EABCO or match grade machine.