Ammunition is cheap in Chaos Fighters and Phantalleum, thanks to the ease of manufacture of the bullets and the use of copy spell, which is very effective only in manufacturing in large quantities. To put things to perspective, a newbie gunner can own ammunition comparable to bullets fired by police officers all over Earth for 125 days without borrowing any money and most gunners have ammunition comparable to that of a legal enforcement ammunition warehouse. But in the early days of battling sport, firearms are useless because of the need of reloading.
However, reloading ammunition instantly after firing them became possible when internal modifications to firearms allowed direct teleportation of the ammunition straight into the firing chamber or magazines loaded into them. With that, battling sports became viable for firearm users as they can just firing practically without needing to reload ever. However, this does not give them an edge over other people as bullets can be dodged, blocked or deflected away easily, battlers are trained to calculate how bullets are fired through looking at the firearms and bullet usually operates at 10% power compared to blades.