BUR #18020 has been approved by @nonamethanks.
create alias bullet_trail -> projectile_trail
create alias tracer_fire -> projectile_trail
I have discussed with few builders and contributors regarding this issue. Bullet_trail currently has no descriptive wiki, while I assume the usage should be for subset of motion lines that indicates bullet flight path (for instance post #6109183) and it is not luminous. As we generally know from the wiki, tracer fire is for glowing linear trail of light left from fired tracer ammunition (post #5753405).
Yes, I think there are significant differences between them visually, but someone gave me an advice that such tags should be more usable generally (not simply catering to firearm "enthusiasts").
I am all for making tagging as correct as possible, while not making tag gardening job a trickier vocabulary check for most users. This proposed alias should be applicable for flying projectiles that are not just bullets:
Updated