You may have worked on hundreds of rifle barrels, but that doesn't mean you have good diction. In this case, your understanding of alignment is limited. And really, do you have to be "that guy?" Does it really matter if I say "fires a weapon" vs "activates a weapon?" They kinda mean the same thing, even though one is more commonly used. But let's pretend you're not invested in 2-dimensional thinking where you have to be all correct and I have to be completely wrong.
You're right, alignment can, and often does colloquially refer to objects in a straight line. I think it's great you threw out a few TMs and FMs. But see above and also consider that there is a book you forgot to mention. It's called a a dictionary, and if you can get past that first part about straight lines, you will see that that alignment also refers to relative positioning of two or more objects. Notice how there is a comma after some words? Or even multiple numbers underneath a given definition? You're supposed to read all of that. Besides what do you do when you have a headspace that is too loose or tight on an M2? You screw or unscrew the barrel and put the gauge in the T-slot between the face of the bolt and rear of the barrel until the GO end enters the T-slot and the and the NO-GO end doesn't. Meaning....SURPRISE...you have just changed the position of one object relative to another (and in a single plane for that matter) which meets the definition of alignment. Mechanically speaking, you are still aligning because you have two mechanical objects that must be in very particular positions in order for the system to work properly. Another example is wheel alignment. Especially thrust alignments where only the front wheels are adjusted. In a situation where you may not be able to adjust the rear wheels, and where one may be completely straight, and the other slightly off (for example), you adjust the front wheels only and get them as close as possible to the thrust line, or the average of where the two wheels point. Certainly, not everything is nicely "lined up" in this case, nor is that the purpose. They are positioned relative to one another to produce a desired outcome, which meets my definition of alignment. Oh, but the distance the doesn't change between the wheels you say, you're just changing angles....because you seem to be an individual who favors 2 dimensional thinking meaning you see yourself as only all right or all wrong. But a synonym for angle is angular distance, or the degree of separation between two objects. And while angles are measured in radians, which is just a ratio of the length of a circular arc to the length of the initial side of the angle....length (or distance) kinda does play a role.
How about a more complex system, such as varus alignment in the knee in medial compartment osteoarthritis? Medial meniscus extrusion is often the result of medial meniscus posterior root tears, and medial meniscus extrusion is critical factor in progressive knee OA. Varus alignment of the knee can be affected by factors such a ligament laxity (meaning the ligament stretches and lengthens), cartilage volume, and bone morphology which includes subclassifications such as medial meniscus extrusion. Want to know what affects varus malalignment and OA progression in the knee significantly, especially hip-knee-ankles angle, medial proximal tibial angle, joint line convergence angle, and percentage of mechanical axis? A medial meniscus extrusion DISTANCE of 3mm or more. And that's one of the ways candidates for high tibial osteotomy are determined. A great example of how alignment is affected by distance.
Wanna talk about spines next? Cervical sagittal translation > 3.5mm (a measure of distance) OR intersegmental angle > 11 degrees meets criteria for spinal instability. I'll spare you that one.
So evidently distance/length IS a factor in complex systems, but you're somehow arguing that it is not in a simpler system? That seems silly. Or you just don't like my word choice because it's not what you would have chosen and decided to put me on blast.
But hey, apologies to the original poster. You were asking about M2s, not trying to see me argue with some guy that got butt-hurt over my word choice.