It makes little difference anyway, because anything that changes the way the double rifle recoils, will also change the regulation of the rifle and it will have to be re-regulated. I'm not talking about working up another load, but re-regulating the rifle with solder, and heat, after any porting is done.

If someone wanted to do this, and I can't immagine why anyone would,

it would be better to regulate after the porting was done, with the muzzle wedges behind the porting.

However, I think the Double rifle Gods would strike you dead for such a sin!