I don't know for sure, but from what he has written, i don't think Mike has looked much at an Accura breech plug. If he has he can fix what i say. Otherwise, please allow me to jump in here.

The flash hole of the Accura breech plug is only about 1/8" long. There isn't enough steel there to 'add much more of a concave end to what's already there. This is why i intend to install a vent liner in said breech plug. Installing a vent liner will allow one to make more of a concavity.

Please forgive me, if my intrusion here is unwelcome.