Something I've noticed is that most guys are pretty good with the smaller guns that they use all the time. Doesn't matter the brand or style with practice we learn how to shoot our guns well.
I've had a few guys come out and try to shoot bluewater using guns that generally spend a lot of time in the closet - it doesn't always go well for them.
Bluewater hunting is different in that we don't usually pull the trigger very many times in a day. It's funny when you think about it, we spend so much money, time, effort, etc. to get ourselves into the position to shoot a fish of a lifetime and we are taking a longer shot than normal while shooting a gun that we almost never swim with, much less shoot, that is totally different from the style of the gun that we shoot every day - logically it makes no sense, yet it is generally what most people do when the go bluewater hunting.
I know a couple of guys who hunt well using totally different style guns, but they do a lot of both types of hunting and they know their guns VERY well.
I think the "average" guy who doesn't shoot bluewater much would be much better served to keep the style of his gun the same when going from reef hunting to bluewater hunting. That and even if it means shooting chum with your bluewater cannon, DO IT, you must pull the trigger repeatedly to get a feel for how the gun shoots, what the trigger pull is like, how much recoil to expect, how to reload it quickly, how best to handle it in the water (the extra length and mass can affect your diving) - basically you should know the gun well enough that you don't have to think about it.