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
Your Marlin model 780 was made in the year 1977 with the serial number that you have provided.
you cannot remove it. it is all in one with the receiver frame
To remove the barrel on a High Standard Model 66, first ensure the firearm is unloaded. Then, locate the barrel latch on the underside of the frame and press it to release the barrel. Gently pull the barrel away from the frame until it detaches. Always consult the owner's manual for specific instructions and safety precautions.
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.