Double-check the subject? "when armor has out-paced armor"

"How does this affect infantry warfare and more specifically guns": what is this "infantry" you are speaking about? You mean set-piece battles, with battalions maneuvering on a battle field? Isn't this pretty much obsolete? Modern infantry is quite well protected against small arms fire already; that's what machine guns are for, and why close artillery and air support are so important.

Armor isn't magic. Even if you made an armor that could prevent a .50 caliber bullet from penetrating, the energy from that bullet is still going to be absorbed by the body. And if your armor is really lightweight, it won't dampen the impulse much either. So even if the armor is perfect, a single .50 caliber bullet is going to transfer roughly 14,000 ft pounds of energy into your body at close range. In comparison, a punch from a heavyweight boxer might impart 300-400 ft pounds of energy. So a large caliber bullet like a .50 cal will likely kill you even if your body armor stops it.

Very true. I'm just wondering what the standard infantry can luge around with there assault rifles that can compete with this armour. While it is true that the Russians have weapons like the Ash-12 which is basically a 50 cal assault rifle. The logistical issues (Supply, carry weight, magazine capacity etc) of such a rifle would probably make militaries look for other options. If there are any.

@DanielPoirier go caseless, caseless ammunition is a lot more lightweight and compact, if their material science is that advanced making the rifle lightweight is easy as well. Making a rifle that only weighs 7 or 8 pounds is not hard at that point.

Good point, very good point. I initially was hesitant to think of caseless ammunition due to the fact that it crumbles. But if the the material science is advanced enough and combined with perhaps a 8mm or 10mm bullet with some kind of armour piercing core...very interesting

There are similar historical accounts of armor outpacing weapons. The first to come to my mind were the first ships clad in iron. They seemed almost invincible during the US civil war. If I recall, there was even a battle between 2 of them which was a long, futile effort of shooting each other in vain. I only had a couple minutes right now, hopefully this is the right link to get you started: en.wikipedia.org/wiki/USS_New_Ironsides

hi, how common is this type of armour? often high-end quality armours are expensive and so only the wealthiest can afford them.

Unless it's a full-body armor including a helmet (think Halo), anti-personell-landmines and/or explosives would be effective countermeasures, since the guy in the armor still can be killed by pressurewaves.

@DanHanson if you have a lightweight framework and say several CNT strengthened spidersilk layers draped over, then the force of the bullet is spread over the framework before it goes into your body and while it may seem miniscule the extra time taken for the bullet to slow down is a significant drop in force taken.

@DanHanson Are you using foot-pounds as a unit of energy? I've never seen that and I've taught a handful of college freshmen intro physics classes. I get torque and energy have the same units, but it's always newton-meter for one and joule for the other. Is there a field of science that actually uses foot-pounds for energy?

Carbon-fiber is electrically conductive. That could be an exploitable weakness.

@user1717828 it's common in firearms talk, which uses a bunch of weird units. I guess if you consider that a barrel is of order 1ft long, you can think about it as the work required to lift x/g pounds a foot against gravity to get some sort of intuition for it?

You don't even need high caliber. You shoot 500 rounds of 9mm into someone with the top of the line body armor and they're still dead. Same concept. 500 rounds of 9mm is a lot of energy, and that turns your target into jelly, regardless of what you wear.

@Loduwijk: Battle of Hampton Roads between USS Monitor and CSS Virginia.

Oh, I know that caseless ammunition is a thing. I was hesitant at using it at first due to its...issues. though, considering the material science to make this armour, i believe that those issues would be greatly reduced.

@John, I would NOT want to try to shoot a .50 BMG from a rifle that only weighed 7 or 8 lbs. A .308 hurts bad enough on the shoulder. Unless you have extra padding or support a .50 would be tremendously painful.

@user1717828 A lot of us gun nuts don't have any truck with your weird space points :) Seriously, the conversion would be from foot pounds to joules. .50 BMG would likely be around 16000 Joules hitting the target. compare to a 9mm with less than 500 joules. middle of the road 7.62 would have around 3000 joules.

@PaulTIKI the weight of the firearm has less of an impact that how good your recoil absorption mechanism is. The US army used to make recruits put the stock against their crotch and fire automatic rifles to get it through their heads these were not their daddy's hunting rifles and actually had good recoil absorption.

@John I know about that as it applies to the 5.56 since I did exactly that in ROTC many years ago. The thing about the .50 BMG is that you are talking about orders of magnitude more energy so the engineering is going to be Non-Trivial to keep it within a 7 lb mass. Many modern sniper rifles are Bolt action and could be more easily reduced in weight, but all of that recoil goes right into the shoulder. One could reduce weight by shortening the barrel, but that sacrifices accuracy. I like the idea of being able to hit the target from 2 miles away.