This has been a topic I've always been curious about in RWBY. How exactly does dust ammunition work? Is it really deadly? We've seen Coco use her mini-gun to literally cut Nevermore in half, but in V5 C10 we see the White Fang's ammunition get blocked by Kali with a serving tray. Is there inconsistencies with the strength of dust rounds or is there a logically explanation for both extremes? I'm gonna present what I think the answer is but I also hope to here what you think.
First point is, what does a dust cartridge look like and how does it compare to a IRL bullet. Well, the one time I can remember seeing a dust bullet was in V2 C11 when Weiss hands Blake a magazine for Gambol Shroud. The magazine contained 6 colored cylinders that look more like the cylinders in Myrtenaster (except shorter) than bullets. From that, I think dust ammunition just fires dust's "magical" properties rather than bullets. Further evidence to support this is in the Mercury vs. Yang fight of V2. Mercury fires a bunch of rounds of neutral colored (what I'm assuming is standard, but might be air) dust ammunition around Yang. Instead of just being bullets circling her, it's blobs f white colored dust circling her, suggesting there isn't a solid projectile. Another example is in V5 C10 when Blake shoot ice ammunition at Ilia. When a round hits Ilia's weapon, it freezes, further suggesting that dust ammunition just possess the properties of the dust being used, and not a solid projectile.
There is a catch to this though, and that's Coco. She clearly has an ammo belt on her purse/mini-gun with very real looking bullets. Her mini-gun also has a large drum magazine like what you would see in real life. One thing we don't see is shell casing being expelled from the gun or laying around where she was firing. This either means spent casings are still housed in the drum magazine, or there are no casings at all and dust ammunition is like I stated in the paragraph about and has no solid projectile.
That brings me to where this all comes together. Is dust ammunition really that deadly in the world of Remnant? Can it both cutting through a Nevermore and and still be blocked by a serving tray? To me, that depends on if Coco's mini-gun uses a solid projectile like a normal bullets, or acts like the dusts rounds analyzed in the first paragraph.
If Coco uses realistic bullets:
Then there are 2 main styles of dust ammunition in circulation. There is ammunition that uses purely dust and isn't very deadly, and seems to be the majority. This style is used more for the "on hit effects" like freezing things using ice ammunition or leaving behind stone copies of yourself like Blake does. It may also be used to redirect momentum like we see Ruby use to cut through big targets, or Yang use to deliver powerful punches. Then there's the more realistic, and deadly, ammunition that Coco uses. The kind that can shred through huge creatures with ease.
If coco uses the same type of dust ammo as everyone else:
In this case then maybe there are just inconsistencies with how powerful a dust round is. Perhaps the longer barrel length or larger ammunition of the mini-gun makes it exponentially more deadly than the pistol style weapons we see most other characters use.
Another interesting thing to note is how guns are used in Remnant. They're secondary weapons. This is completely opposite from our world where you wouldn't bring a knife fight. There are only a handful of characters in RWBY that use a gun as the primary form of their weapon. Why? Is dust ammunition really not as deadly as a blade or hammer? Or is it purely for the aesthetic of having characters using swords and melee weapons rather than just having fire fights? We haven't seen any human or faunas killed by a bullets alone that I can remember so perhaps because of the superhuman speed and abilities of the huntsmen and huntresses render most people unable to hit them on the move so they rely on blades. I'm not really sure, but I would love to here from all of you on this topic!