Is the armor worn by knights bulletproof?

Answer 1

yes

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Sorry, no, the armor worn by knights is not bulletproof, unless the bullet has very low energy. In the Renaissance, when personal firearms first appeared, armorers made heavier armor than had been used, and tested it by a firing musket into it, with the dent being proof that the ball had not penetrated. The problem is that they were never able to make armor heavy enough to withstand the heaviest musket balls, without making it too heavy to be worn.

The mounted knights had long been in trouble before the introduction of gunpowder, because their armor was not arrow-proof. They were cut down by the hundreds when they charged against the English at Agencourt, and the thing that was most murderous was the English archers.

The Real Answer:

Yes: most of the high quality Milanese armours of the 15th/16th Century were bulletproof to a greater or lesser degree and these "harnesses" were of a comparible weight to the armour and equipment fielded by today's soldiers (50-70Kg)

At the time of Agincourt the reason why english archers were such an integral role in the battlewas not becuase the bodkin could pierce the armour (it couldn't) it was becuase the arrows killed the horses trapping the knights underneath the horse or leaving them to slog their way through the churned mud towards the english line.

Samurai in 16th-19th century Japan bought and maintained western style plate armour that was tameshi gusoku or bullet-tested armour with the last recorded use being in the 1877 satsuma rebellion.

Australian outlaw and folk hero Ned Kelly was famous for winning gun-fights against the police using his cobbled-together plate.

the reason for the decline in armour was more due to it being extremely expensive and the impossiblity of fielding a large force of steel clad Man-at-arms.

So yes Armour can provide protection from gunfire though I would point out that Steel Plate has NOT been tested against modern ballistics and I would advise you NOT to test it out for yourself.

AnswerIt, of course, depends on the time period. I'm assuming you are comparing armor to firearms available at the same time.

Early firearms were notoriously inaccurate, slow to reload, and generally with poor ballistic characteristics. However, from the outset, they were able to easily penetrate contemporary chainmail armors at "reasonable" (50+ yard) distances. Shortly after their introduction in Europe (roughly mid 1400s), plate armor makers began to thicken breastplates and helms in an attempt to stay ahead of the increasing power of firearms.

For about a century or so after their introduction, the better-quality breastplates were "proofed" by firing bullets at them, to indicate their trustworthiness. So, YES, the better quality breastplates were bulletproof from a contemporary firearm, up until the early 1700s. However, none of the other plates of the armor suit (legs/arms/groin) recieved the same upgrading, as it required ever thicker armor to remain bulletproof. And, of course, armor made a few decades before would no longer remain bulletproof against the current generation firearms.

With increasing enhancements, particularly the introduction of the flintlock, the muzzle velocity of the bullet became too high to be able to protect against, unless one wore a suit so thick as to be impossible to move in.

Thus, there was a period of "qualified immunity" between 1450 and 1650 or so, in which time a current armor suit could stop a current-generation firearm's bullet if it hit the breastplate.

Oriental armors were of such construction as to never be reliably bulletproof against contemporary firearms, though, as noted above, they did import western-style solid breastplate armors well into the 1700s.

Ned Kelly's famous "bulletproof" armor wasn't real armor; rather, it was a 1/2 inch thick cast-iron plate that he wore over his chest only. It was more of a very primitive precursor to the modern-day flak vest than a suit of armor, and was so heavy and bulky as to be nothing more than a curiosity (certainly not something usable by an army).

Finally, the real reasons for the decline of personal armor was in fact the increasing effectiveness of firearms. By 1650, a flintlock smoothbore musket could reliably punch through any thickness of armor plate suit worn, at ranges over 100 yards. With the increasingly cheap production of a flintlock came firearms proliferation, meaning that armies were now being equipped with large fractions of firearms; against such massed firepower, an armored man could no longer be sufficiently protected to enable him to close to melee distance. That is, the range at which a firearm could reliably kill an armored opponent was much greater than melee weapon distance (or, even charging distance when mounted), so armor was no longer effective (and, being no longer effective, was abandoned). Cost had nothing to do with it - indeed, large armies of steel-clad soldiers had been fielded throughout the medieval period (over 600 years prior).

Answer 2