I looked for over 2 hours yesterday, even tried converting tf_weapon_particle_cannon.ctx (from tf2_vice) to .txt (using valve's ctx converter) to see what explosion effect it says in there but it was the same as the default launcher, i also looked through tf's vtf files and in there found drg_cow_mangler.pcf, it was full of nulls and random characters but between them there was stuff like "drg cow explosion", when i tried using this i got the default explosion effect, on the valve particles list site cow mangler isnt there probably because cow mangler was either added after the site was made (2010 iirc) or the explosion effect was updated after that, also everything i mentioned i tried by updating tf_weapon_rocketlauncher through both a folder and a .vtf directory from the no smoke explosions thread.
(@wrub1x)
Also some of these file names i mentioned might not be 100% correct because i'm writing this all from memory.