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Context:

This armour was designed to be a full-body "bulletproof" suit, only capable of stopping bullets from military assault rifles that have the same capabilities of today's ones. Of course, the design has a big part on this question, so let's say they work like deep dive suits, which use something akin to those "three bearing swivel nozzle" mechanisms as an articulation.

Not because these (today's assault rifles) will be exactly the weapons of this history's scenario, but because I believe it will facilitate the question. It is easier to asnwer using something that is real than something that isn't. And I "just" need to change a few things from the answer to fit in the history.

In this scenario they are build to withstand even 50 cal, but you don't need to actually use this as a base to your answer if you don't want. And again, it is easier to think/answer using real world bulletproof materials to base your answer on.

Its weight and other things aren't a big concern for this question, but if you include these, no problem.


So, the problem/question:

So, The articulations/joints/bearings wouldn't be as thick as in the image of the deep dive suit, but my biggest concern is how "pierceable" these bearings would be in an actual gun fight.

So, using conventional ceramic/metal bulletproof plate materials (in the same thickness or not), how well bullets would be able to just go through these joints?

I searched about tank armor and its vulnerabilities, like when two armor plates connects in different angles, because I thought it would be useful for this matter, but I couldn't find results.

(Of course, some shots would eventually distort the plate/joints and the rotary mechanism would fail, but that's not my concern because of some reasons that doesn't matter to this question.)

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    $\begingroup$ I think there would be a lot of engineering design breakthroughs to get conventional materials to stop assault rounds consistently. Most of these would need to improve limb and articulation designs. Have you considered powered armor where the person is in an armor pod with mechanical limbs? It eliminates joint issues, since they become engineering (and also disposable - blow off a mechanical arm and keep fighting). $\endgroup$
    – DWKraus
    Sep 24, 2022 at 0:06
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    $\begingroup$ Consider liquid armor. It's basically bulletproof oobleck. science.howstuffworks.com/liquid-body-armor.htm and en.wikipedia.org/wiki/Liquid_Armor $\endgroup$
    – DWKraus
    Sep 24, 2022 at 1:01
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    $\begingroup$ You can also minimize the need for arm flexibility with a head-tracking shoulder turret for weapons. Or have armored sleeves extending down from the arms/legs to cover the joint from the most vulnerable angle (akin to some samurai armors) $\endgroup$
    – DWKraus
    Sep 24, 2022 at 1:31
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    $\begingroup$ the face plate will always be a vulnerability we don't have anything that transparent, thin, and bulletproof. even bulletproof acrylic is like 4 inches thick, and once its been shot it is no longer transparent. $\endgroup$
    – John
    Sep 24, 2022 at 15:01
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    $\begingroup$ @John Aluminum oxynitride might interest you! It provides the same level of protection as acrylic/polycarbonate but at less than half the thickness. $\endgroup$
    – Niras
    Sep 27, 2022 at 2:58

3 Answers 3

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You say weight and size isn't an issue but those are absolutely major issues with modern materials. There's a reason we haven't made any full body bullet resistant suits in real life.

I am assuming you are referring to the .50 BMG and not something like the .50 AE or .50 Beowulf when you state .50 cal. The .50 BMG is an anti-material round that can punch through an inch of tank-grade steel armor from 100 meters away.

The joints and plates of the suit would need to be ridiculously thick and heavy to be effective against that sort of firepower. You could make the suit lighter by using composite materials like ceramic and UHMWPE but those need to be thicker than steel to get a similar performance so your suit would be even bulkier. There are similar issues with titanium or aluminum alloy. And that isn't even including the massive amount of padding you'd need underneath the plates.

For reference, the deep dive suits you give as an example are extremely heavy. A more modern suit weighs approximately 500-600 pounds. And even then they are not bullet resistant to any significant degree.

Making armor proof against intermediate cartridges (5.45, 5.56, 7.62) used in modern assault rifles would be easier but still not exactly man portable. AP ammunition means that the joints and plates would still have to be >12mm thick.

At the level of performance you require you're better off with a mini-mecha like DWKraus mentions or else you would require some form of powered exoskeleton to move.

But theoretically, if your joints are the same thickness and material as whatever plate material you are using they should also be bullet resistant to a similar degree.

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There are three answers to this based on how the armor is intended to be worn and the material technologies available to the users.

My first answer is considering this material to be incredibly thin and strong and the person inside to be the only thing propelling the armor. The armor wouldn't need to penetrated to kill or incapacitate the person wearing it unless they were augmented somehow. Shooting the very end of those limbs would cause the things to swing backwards with enough force to snap the joints within beyond used.

My second answer to this considers the material to be just like before, but the humans within to be augmented with either an exoskeleton or an additional endoskeleton system. So, despite those joints being horrible for mobility, it is entirely possible to create them in such a way that they're mostly impenetrable. The only caveat to this is the binding method used. A hail of many .50 rounds could either dislodge the fasteners or foul the bearings/bushings enough that they would be immobilized.

My final answer to this considers the material to be the same again, the humans within the be augmented again, but this time the joints to have a shroud around them with an essentially perfect seal. In such a situation, you would have zero hope of destroying it with man-portable arms except for anti-tank weapons.

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If the plates of the armor are strong enough, then the joints can be protected very nearly as well. Here is how. This is King Arthur's armor from the 1981 movie Excalibur. Note the overlapping plates. And the "fins" that would protect the neck joint when the helmet is added. This dramatically cuts down on the angle a bullet could come from and still penetrate.

This particlar armor was designed to look good on camera. (And was probably made of spray-painted plastic, considering that the actors were able to walk around while wearing it.) But one could easily imagine optimizing it for protection from bullets.

It adds to the weight, of course.

enter image description here

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  • $\begingroup$ This touches on a common misconception about full plate armor/plate harness. Unless it was a specific, jousting-of-peace tournament-only armor, a fully armored knight can do nearly everything a modern armor soldier can do. Historic accounts talk about armored knights dancing, running, and climbing ladders upside down! Don't believe me? Check this out: youtu.be/pAzI1UvlQqw $\endgroup$
    – PipperChip
    Oct 4, 2022 at 15:15
  • $\begingroup$ The folks you are referring to would typically have done a lot of practice in the armor. That is, they will have muscles and bones and such that have trained for it and so can take the load. Your typical actor won't have that. $\endgroup$
    – BillOnne
    Oct 4, 2022 at 16:02
  • $\begingroup$ That's just a note for anyone who misinterprets that parenthetical statement on your answer, that's all. Also, IMDb seems to think the armor from Excalibur is made of aluminum! (m.imdb.com/title/tt0082348/trivia) That's lighter (and more importantly, easier to work) than iron/steel, but not negligible! $\endgroup$
    – PipperChip
    Oct 4, 2022 at 17:13

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