Reflex or Red Dot Sight Question

[Chainsaw2]

I'm thinking about getting an AR15, and adding either a reflex sight or red dot sight. I hear they're both good, but have no experience with them. So, my question is:

With a 20" bbl and 55-60 gr. slugs, using these sights, what is the effective range of this combo on say an 18" circle?

Thanks!

 

[trickyasafox]

I cant say to your particular set up, but I run a 16in carbine with a reddot (4moa dot) and paper plates at 100 are fairly easy. I would think depending on your final setup, 18 inches (chest sized targets) would be fairly easy hits to 300ish yards

 

[Chainsaw2]

Thanks!