That certainly is an exposed cap in my book - and you are sure that Winchester still offers a #11 breech plug for it?

I was not sure about your 150 but I do know the Firebolt is exposed....

That really looks like a good wrap on your BP - that extra tape on the outside of the plug is a neccesity also as the the first primer will blow some of that tape into the threads at the rear of you barrel and seal those threads also... I am assuming you have a overwrap on the nose of the breech plug also....