yes there is a ring around the barrel that can be tightened. You might have to remove the barrel first depending on how old it is because some of them you could adjust with the barrel on the gun and the older ones you could not without removing the barrel but both are easy to do.
The Browning Challenger (Belgium made) first model barrel has a removable half circle shaped approx. 3/16th inch insert (which is part of the barrel) which creates a tight fitting once you tighten the barrel screw. This may be missing in your pistol and the best way to check it is to remove the barrel, turn it sideways, and if a hole is showing above the "V" shaped lower part, then that's why it's not tightening up as that part is missing. BT100dc
Nice rifle. I think the youtube will get you there. I have the Mirouku version and the ring around the chamber part of the barrel will need to be turned counterclockwise as you are looking from the rear of the gun.
It is hard to turn and makes a click for each adjustment. Don't try it with the barrel on the gun. It is easy to grab the stock and damage the wood if you are holding it while trying to twist the locking ring
I'm assuming the Mirouku is the same design as the Belgian.
The Jap version is somewhat the same as the Belgian version. But over the years it has changed some. The original Belgium versions did not "click" but where adjustable. The later ones have a small pin that has a spring behind it that does "click". The round ring has also changed in side and shape over the years. Some you can adjust with the barrel on the gun (the ones that click) but to really get it tight you might have to take the barrel off but some of the older ones you cannot adjust unless the barrel is off the gun.