Edit: Be very careful with that 777. The suger ring/can't seat bullet deep enough/barrel obstruction is very real with that stuff. Bought some of the pellets a few years back. 3 shots and I was done with it. Put a mark on your ramrod to be certain you get seated deep enough. Plus it didn't have the wonderful rotten egg smell.
This brings up one of "Doyle's tricks" to get good accuracy. When shooting at the range ALWAYS, ALWAYS, ALWAYS, remove the breech plug and do a wet swab between every shot. That is the only way you can be 100% assured that the shot you make on a deer (from a totally clean barrel) will match with what you sighted in.