Ahhh a bolt action inline muzzleloader
I'm not an expert on them (theres a reason for that
), and don't quote me but I think that gap will close up when you pull the trigger. I believe its like a plunger type inline. Someone with more experience with these things will be along shortly. But That breech plug SHOULD Be snug and not backed off. If you do that you are increasing the distance for ignition and probably can bust the primer allowing gasses to escape rearward. If this thing operates like I think it does.