Jim, a plug bayonet grip would fit rifling if the inner bore diameter was less than the grip diameter.
Rifle bores were generally less internal diameter than musket ones. The early UK Baker rifle of 'Sharpe' fame had a 0.625 in. bore. the Brown Bess smooth bore musket of the same era had a .75 in. bore.
As rifles and powder improved, rifle bores got smaller, the American Pennsylvania ((sometimes known as Kentucky) rifle had a bore around .36, and the similar Plains rifle was ~.45. This bore size is getting too small for a stable dagger tang & grip. Even the ubiquitous American Civil War Springfield rifle only has a .577 in. bore for it's Minié ball & cartridge rifles of the mid 19c were trending towards .45 and late 19c to .30. Flimsy Rat tail tangs would be required!