They are 35mm and 40mm respectively.
Their power difference isn't substantial, but in Oasis Town and even in the Holy Spring Sect's domain, the popular choice is 35mm caliber.
Most grenade launchers also use this caliber.
Moreover, making grenade launchers is quite simple.
There's no need for an accuracy of 0.1mm or even smaller error precision; typically, a cylinder fitted with a striker and launcher suffices.
Many rifles have a dark cylinder attached beneath the barrel, serving as a grenade launcher to supplement the firepower output of a soldier.
It's similar to a signal emitter.
In essence, the grenade launcher delivers a hand grenade with greater precision, projecting it hundreds of meters away.
Although for Late-stage Enhanced People or Evolvers, throwing a stone the size of a fist three or four hundred meters away is not surprising, the issue is that a hand grenade doesn't necessarily explode right upon hitting the target.
