It's this group that's been doing the scanlations for this series actually. They just never uploaded the first 2 chapters cause another group did them.
4 rounds per second is nothing. You can fire more with a revolver. I reckon it was meant to be 40 per second. That would be something in a world with no highly developed firearm technology (no fully automatic weapons before that).
Rereading this, something I noticed: the orcs are really brave in this chapter, still fighting even after seeing such a powerful enemy decimate their comrades.