First, an obligatory safety message: airguns are dangerous, and should be treated with the same safe handling practices as firearms. Do not replicate what was seen/done in the above video. Please note the rifle was degassed for this, for safety reasons. Even still, this violates several best handling practices and should not be copied.
So what exactly are you seeing here? Well, this is a .30 caliber Smooth Twist X barrel on an FX Crown. Note that the camera starts rotated approximately 90 degrees clockwise from vertical, and so the brass transfer port actually appears on the right hand side.
0:00 First you see the bolt probe, slowly being retracted, and the magazine indexing a pellet. Note how rapid/violent that is. It really chucks that pellet sideways surprisingly forcefully. No wonder groups shrink when pellets are single loaded as opposed to magazine fed.
0:13 The pellet starts to be fed forward. Again keep in mind the camera’s rotated perspective. The pellet slowly noses its way forward.
0:21 The pellet visibly engages the rifling here, showing slight deformation at the points. Notably, this is key to good accuracy on most airguns and firearms, firing the projectile before it has engaged the leade will tend to result in poor accuracy.
0:36 We’re just examining the bore here. Note this barrel has not been cleaned at all recently, so lead buildup should represent normal use. The majority of the bore appears quite smooth, although far from flawless as there are clear tool marks of some sort at various points. Notable is the leading of the lands, while the grooves appear remarkably untouched.
1:07 Now we’re at the choke. I would recommend you pause the video here, click the little gear in the bottom right hand corner, and set the playback speed to 0.25 (1/4 normal speed) and watch the whole thing carefully, potentially multiple times. It is VERY interesting. Its significance is difficult to fully discern, but the leading certainly suggests the pellet goes from riding the lands to being constrained by the entire bore in a very short distance. There is also, at least the appearance, of the lands getting wider toward the muzzle within the choke.
1:14 Out of the bore and into the liner system. Visible here is the liner retention tubular bolt and the inside of the internal shroud brake.
So what all this means is very much subject to interpretation. There is a great deal of speculation regarding the Smooth Twist and Smooth Twist X systems, how they are similar to and different from conventional rifling, etc. So here it is, a solid video showing a peek behind the curtain of what exactly is in the bore. Hopefully it is interesting, if not otherwise useful.