Phased plasma rifle in the 40 watt range.
If you want something sci fi but conceivable with foreseeable technology, there have been proposals for man-portable railguns.
Just what you see on the shelf, pal.
I think everything I was going to post has already been discussed
Guns/bullets that do most of the aiming for you
Smart bullets that explode at the right distance (in case someone is hiding under a window or taking cover)
Guns that can distinguish friendly from hostile targets
Guns that will not work unless the authorized person is holding it
Guns that are held by remote controlled robots rather than by soldiers
Aside from that, I don’t know.
Someone will finally be able to shoot a regular-load Browning .50 caliber cartridge through a hand gun. Next challenge: a regular 20mm cannon shell from a vulcan cannon.
How about ammo which uses a primer-type charge to get the projectile out of the muzzle, then a solid rocket fuel motol for acceleration?
Low weight, the barrel does not over-heat, and minimal kickback.
Do I win?
Beats the hell out of a bullet which has to spin x rpm at y fps - as the distance-measuring ammo.
And how precise does the rifling need to be before you get to the point that each weapon needs a dedicated ammo production line to make the telemetry work?
Has there been any recent (post-ACR program) development in flechette weapons? Those are the one sci-fi staple that actually had working models, unlike your lasers and plasma rifles.
That’s why it’ll be near-term! The advantages are huge if the technical kinks can be worked out.
How much of your average round’s weight is the cartridge case? How much of the production cost? How much money do the cartridge cases cost the military to ship a million rounds of ammunition to Afghanistan? How many weapon malfunctions are due to failures to extract or eject the cartridge case?
All of these can be mitigated to some extent with a move to caseless ammo.
They said the physics were impossible!
I think that there will be a breakthrough sometime where we wind up with laser weapons in a pistol-style format.
2020s style Death Rays.
You can get a laser powerful enough to use as an antipersonnel weapon. Except you’d need to mount it on a Humvee to carry the necessary power supply. And if you had a choice between a Humvee that mounts a temperamental multimillion dollar laser that kind of works, or a Humvee that mounts a cheap effective reliable machine gun, which do you choose?
The problem with lasers or particle weapons is that there’s no conceivable breakthrough anywhere on the horizon for powering the things. If you can come up with a battery or capacitor that could power a useful small arm laser, the power supply would be 1000 times more revolutionary than the weapon. Make that 10,000 times.
Batteries like that will lead to the biggest revolution in infantry warfare since gunpowder, though. Laser pistols, portable railguns, power armor… the technology is all there, just waiting for a power source.
Actually, they did invent reliable, effective laser rifles for infantry. But it turns out they really do go, “Pew! Pew!” when they fire and no one ever wanted to be caught using them.
It’s sort of like bow & arrows. you can use advanced materials to make a very reliable and accurate high-tech compound bow. But physics dictates a maximum performance you can obtain from a projectile launched by a human pulling back an elastic string. We have pretty much solved for the most efficient solution for using small explosions to launch small pieces of metal.
I heard it went “zzzzzzzzzzzaap!”
The energy densities needed lead to Routledge’s Law: “Any interesting battery material for a laser gun would be more usefully deployed as an explosive warhead.”
I’m focusing on the weight of the propellant. There’s been some interesting advances in “bang” that, even if it’s only a few dozen grains of weight reduced per round, can add up to savings in pounds on a kit or in a ruck when considered over the several hundred rounds of ammo each Airman, Soldier, Sailor or Marine’s gotta carry into combat. Less weight = go faster.
I’m not offering a change in caliber or ballistics–I think we’ve reached the limits of physical science there. But maybe shave an ounce off of certain action parts, plastic parts (i.e. the pistol grip on my M-4), etc., and squeeze out some additional weight savings where possible, and it’ll make a grunt’s job just that much easier.
Tripler
Caseless ammo? Hrm. . . maybe there is something there too.
Overzealous gaming geek friends of mine back in the 80’s did way too much research on possible weapons for Twilight 2000, and found some studies which showed that laser weapons have big, big problems, one of the primary ones being that a laser powerful enough to deliver enough energy to a human target to kill it before said human can pull out a rifle and shoot you with a bullet is also powerful enough to blind anybody looking at the target with reflected light if the shooter happens to hit anything made of metal. Permanently. So, everybody on your side needs to wear special goggles that block that frequency of light, which only helps if the OTHER side is also using the same frequency of light in THEIR laser rifles. If you’re on different frequencies, in any engagement, whoever fires first wins.