I am currently running a 507c on my CO gun and really like the clarity of the dot. It is very easy to pick up. I have a Atibal MRD v2 on my open pistol and have considered buying a 510c for my open pistol. I have noticed several for sale in the classified with a mount and have to wonder if the weight is an issue. I would just change the 507c over to the open gun but I will need to buy another mount and don't want to end up with an extra mount if the 507 is to small for the open pistol.