After asking this question about a month ago and not getting a repley. I'll tell you what I found out and why I bought the one that
There are 4 different ones that I know of that attach to the end of your barrel and remind you of a bloop tube.
Fudd Tuners- Don't have a number for him
There is also one that fits between your barrel and stock called
a BUGHOLE TUNER. Don't have anything on it either.
When a rifle is fired, vibrations occur throughout the barrel as the bullet makes its way out. These vibrations cause the barrel to move, usually against the force of gravity that prior to the shot, was applying a force in a downward direction on the barrel.
In centerfire arms, handloaders "tune" or adjust their loads to most effectively stabilize this vibration to a point where the vibration is consistant from shot to shot. The barrel will still move, but the load is tuned to impart a harmonic vibration that is more or less predictable from shot to shot. It is in essence a predictable damping effect on the moment forces acting on the barrel during firing.
In rimfire arms, we cannot tune the load because we don't handload. Instead we find an ammunition that has the most favorable and consistant characteristics in our particular gun. This goes most of the way toward taming inconsistant vibration.
The next step is to install some sort of passive vibration damper, or tuner. The photos already posted are of the type that install on the end of a barrel. They adjust mechanically by changing length. The mass added to the end of the barrel, and then adjusted during firing, changes the moment force acting on the end of the barrel. One spends a lot of time with the best ammo you can find, tuning (changing the length of the tuner) until the most consistant point of adjustment is found. This is the point at which the mass of the tuner, combined with a specific change in its length, dampens the peaks of the waves of vibration in the most effective manner, thus letting the bullet exit the barrel during each shot when the end of the barrel is in a specific place during each shot.
Tuner settings change for each different type of ammo shot.
There are also tuners that are pressure points installed under the barrel, that apply specific pressure between the barrel and the stock.
Do a search on the RFC site for tuners and you may find similar discussions to this one.
When the bullet is fired, the barrel starts vibrating back and forth, much like a string on a guitar. The muzzle of the barrel is whipping back and forth, but as it goes one way, it has to come to a complete stop before it turns back and goes the other way. Theoretically, then, the barrel actually stops its movement for a fraction of a second before it heads in the other direction. Heres where a barrel tuner comes into play. Since the tuner alters the vibration pattern, the shooter is attempting to modify that motion to get it to be at that stopping point, just as the bullet leaves the muzzle of the barrel.
IF all the ammunition is exactly alike in speed, and IF the powder charge is creating exactly the same vibration every time, then, each bullet will leave the muzzle under the same conditions (the theoretically motionless barrel) and its theoretical flight path will be identical to all the others.
In the real world, there will always be a minor difference between the actual speed of the bullets, and each ignition will create a slightly different vibration pattern due to some inconsistancy or other... but to a large extent, the conditions will be similar. The more similar, the tighter the group.