John Blissett worked in London from 1843 to 1877; his son, Thomas, began work with him in 1864.
That rifle seems a bit odd to me at that period, but maybe someone can provide more info. I doubt it was made for any kind of dangerous game, since those guns were usually double barrelled, but maybe the shooter had servants to carry at least one spare rifle. The caliber would be right for big game, as would that style of sights.
The gun appears to be well made, but I strongly recommend against firing. No matter how well made it was, it is now over 130 years old. More important, when that gun was made they did not have the technology to drill barrels from solid steel. The barrel is made up of steel and iron heated red hot then wrapped around a rod called a mandrel and welded by pounding with a hammer. As you might gather, those barrels were not very strong and many have been weakened over the years by rust or corrosion not just on the outside but in the joints between the welded pieces.
It looks like a nice piece and a very suitable decorator.
One suggestion, use the ramrod or a rod at least as long as the barrel and insert it into the barrel. Mark the end of the barrel on the rod, then measure the outside. If the rod won't go in down to the bolster (the part that has the nipple in it), the gun may be loaded! If so, take it to a competent gunsmith or come back to us for information on what to do.