Short and simple are there any actually effective alternatives to firearms as the main alternative for WW1-1920s era aircraft including biplanes and airships?
1: The weapon must be able to be mounted on the vehicle.
2: The weapon must be actually effective at either dealing with hostile aircraft (assumed using similar or the same weaponry), infantry, armored vehicles, or all of the above.
3: The weapon must not be a conventional firearm in any way. This means no self contained projectile that use black, smokeless, or chemical explosive to propel a projectile via combustion. Rockets are an exception to this.
Research and argument:
In short I am wanting to design hypothetical weapons for a universe in which technology has advanced into around 1920s tech generation wise, but there are no fire arms to speak of. Please do not ask why it is massively complicated, and yes gunpowder, fireworks, and explosives exist. No massive cannon artillery, no machine guns, no rifles or pistols in the conventional way.
For ranged weaponry I have come up with several ideas that can be utilized to great effect I feel. These being mechanized crossbows using compressed gas to cycle a feeding mechanism and reset the tension system which can either use a conventional bow shaped tension bar or even springs. Think something like how the Hellsing crossbow functions in the movie, but actually plausible. These crossbows can be semi or fully automatic. There would also be large mounted ballista type weapons for the equivalent of cannons that even have explosive tips for armor piercing capabilities.
Another ranged weapon I have an idea for is simply a high powered air gun. Lethal air guns have been around for quite a long time. We’ve had air guns since 1580 and they were used to hunt big game like boars and deer from the 17th to 19th century and could reach velocities of over 1000 feet per second. There have also been airguns used in war such as the Windbüchwe or the Girandori rifle, both of which were noted to have great lethality and effect when in the hands of experienced marksmen. So simply I thought that considering the lack of conventional firearms would cause significant advancement into airguns. These would mainly exist as either the equivalent of bolt action requiring manual cycling of the ammunition store or semi automatic. There would also be fully automatic handheld and mounted airguns.
Expanding on my airgun idea, I also thought of utilizing large caliber air cannons to deliver explosive payloads, as well as armor piercing rounds that could have internal rockets that aid in propelling the projectile further through the armor. This idea is a logical upscaling of airguns and draws inspiration from historical weaponry, such as the dynamite cannons used on the U.S.S. Vesuvius that had a range of over a mile and were capable of blowing cellar-sized craters into the earth.
Next up we have rockets as these could be a really good ranged weapon. Unfortunately you won’t see any Gyrojets here as those were kind of a laughable failure. My main ideas for rockets would be to use them as long range artillery in the form of Katyusha-like launcher systems as well as anti-vehicle weapons.
There are various other weapon ideas I had such as compressed air grenade launchers, flamethrowers, and electrified melee weapons, along with air or spring propelled tasers. Bolas and electrified nets fired from guns were considered as well.
The problem I am having is a coming up with a creative and effective ranged weapon for air-to-air dog fights and anti-infantry ground attack runs for aircraft. Crossbows are not the best idea unless they're explosive tipped or fully automatic, and specifically constructed to function on a plane. While I like the idea of using airguns for planes, and having large air machine guns that can utilize the extra power from the engine and additional air from the intake to fill the compressors easily, for some reason it doesn't feel as satisfying to me. It seems like it's just a "gun reskinned" and lacks creativity.
Finally, small air-to-air unguided rockets with a small explosive payload mounted in rocket pods have been proven over and over again in real world combat and rockets were used to great effect by planes in WW1, but if the rockets are too large then ammunition would be very limited, and if they are too small they could be underpowered.
Ultimately I want to form a creative solution to all of these problems, hopefully using a mixture of all the ideas I came up with and possibly hear any weapon concepts I may have overlooked or have no knowledge of. Any help would be appreciated.
(Also sorry if my format is off, my grammar or writing is bad, or this ask just doesn’t make any sense as I am writing this late at night and this is my very first post here.)