The Hodgdon Triple 7 pellets have been formulated to approximate the Pyrodex pellets, so a 2 - 50gr pellet load of either ought to give practically the same results.

About the only thing between the two to be concerned about depends on your ignition method. The 777 pellets were designed specifically for 209 primer ignition, so if your gun uses #11caps........there "might" be some ignition problems.

Also, the 777 will leave less fouling behind, but what it does leave will tend to be hard & crusty.