Who made it? Is it a shotgun, rifle or handgun?
Yes, you can remove the barrel of a model 66 Shotgun!
Best left to a gunsmith.
hire it done.
It would help if you stated the model.
with a torch
you cannot remove it. it is all in one with the receiver frame
Your Marlin model 780 was made in the year 1977 with the serial number that you have provided.
You really want to let a gunsmith do this.
You don't - you'd need to take it to a gunsmith for this.
Best left to a trained and equipped gunsmith.
Your Marlin model 780 was produced in the year 1977.
Your Marlin model 780 was made in the year 1987.