[Philip Dyer]

This perplexes me, I got into a discussion on why plate armor got heavier with the development of firearms and this guy said this.
Unlike you, I'm not drawing conclusions from anywhere, it's a documented fact that armourers that specialised in producing quality armour like Greenwich armoury and some guilds from South Germany which before 17th century used only hardened steel for their armours suddenly stopped doing that for a reason I do not know.
https://www.youtube.com/watch?v=mxQ2q2KSmk8
And lastly I would like to point out something that many doesn't seem to notice. The actual reason that caused the armour weight to increase was not the ever increasing power of firearms, but rather the response of armourers to it: if before 17th century armourers used steel and hardened steel to produce armour, then in 17th century almost no armour was made out of steel.
This perplexed, why would armouried would spent so much time and effort figuring out how to made armour out of high quality hardened steel plate armor suddenly stop making it, even for the wealthy. Can anyone prove or disprove what this guy said?

[Ralph Grinly]

Fighting styles/fashions changed. Armies took on what we today would consider a more 'professional" style- large bodies of infantry, cavalry. The nobles who *used* to take part in battles in armour now wore fancy uniforms - the need for armour just faded away, especially seeing that, as firearms improved, armour had to get heavier and heavier to prove effective.

[Mike Ruhala]

I'm not sure I precisely follow what you're asking but...

Early steels weren't anything as good as what we have now. In the 17th century you'd have been more likely to experience a brittle failure on your breastplate than an actual puncture so the solution at the time was to go much thicker, usually around .20"+ at the deepest spot, and use a more malleable metal, wrought iron even. Nowadays firearms are way, way more powerful but our steel is super good, too. A .25" thick piece of heat treated alloy steel can stop full powered rifle rounds as long as they don't have a hardened penetrator and/or exceed a certain velocity threshold... somewhere around 3,000fps IIRC. It's actually pretty cool in a way, if we had the smiths to do it we could make replicas of 17th and 18th c. bullet proofed cuirasses and they'd work against a wide range of modern firearms. The improvements are across the board actually, modern 14ga stainless steel will stop many modern handguns.

Firearms alone didn't really chase armor from the battlefield, we could always make some kind of breastplate that would stop most contemporary small arms and every century saw such armor in service in at least a limited capacity. The big issue is overall loadout weights... a sword weighed 2 or 3lbs, a rifle-musket weighed more like 10lbs and then there was ammo to consider.

[Philip Dyer]

[Neil Bockus]

I agree with his statement, overall. Based on what I've read, armor quality drop during the 17th century had largely to do with the change in clientele: the rise of mercenary, then professional armies, and economics. Dr. Alan R. Williams had pointed out in his 2003 book "The Knight and the Blast Furnace" that armorers of Nuremberg had stopped hardening their armor regularly by around 1540, and that orders out of Nuremberg increasingly were for munitions-grade and export armors (pg 596-597). And while the knowledge of how to heat-treat metal wasn't lost (clocks and gun barrels from Nuremberg around this time were still heat treated steel), many of the export armors out of Nuremberg by the 1570's were made of wrought iron, rather than steel (Ibid).

Generally speaking, from Williams' book, most of the great armor producing cities in Germany/Austria ceased producing properly heat treated armors from between 1580 to just about 1600 (Anton Peffenhauser was one of the last armor producing masters of Augsburg, dying in 1603). One of the last extant Greenwich armors for which an attempt to heat treat was made dates to 1612. The shift from heat-treated high-quality steel to low-quality steel or iron plates of increased thickness made economic sense given the movements in military structures. Instead of taking months to produce a high-quality harness and risking a breast plate or bowl of a helm cracking during a quench and temper, costing more time and money or hiring someone skilled enough to do it properly, it was easier to just make a thicker plate to improve its resistance. Williams explains on pg. 948 of TK&TBF: "Increasing the thickness from 2 to 3.1mm will double the resistance, and have a similar effect to the use of hardened steel at a fraction of the cost." Now you didn't have to pay top dollar for decent protection, nor risk delays to production schedules to make 1500 breast plates by the end of the month because of botched quenches, and you could mass-produce armor of fair resilience. Problem is, the wearer had to endure thicker, heavier plates.

Not all 17th century armor was ridiculously heavy, however. From my own research, there's a few 17th century 3/4 armors that weigh down in the 30's of pounds. Others get up into the 80's. It is important to remember that many of these are composites. Among the 55 3/4 armors (as displayed) that I sampled, the average weight was 46.5 pounds, but unlike head to toe plate armor of the 15th-16th centuries, which had a pretty tight grouping across time (110 out of 150 weighed between 40 and 59 pounds, avg. 51lb 15oz), the 3/4 armor range was much broader.

[Dan Howard]

Williams has a table listing the thickness of around 120 breastplates dating from 1470 through to 1685. For the first 50 years or so they are all pretty light - around 2-3 mm. After this they vary greatly in thickness from 2mm up to 8mm. The only breastplates he lists after 1635 are cavalry ones, which seem a little heavier than infantry ones. I don't see any trend of them getting heavier as time goes on. The only trend I see is that cavalry armour tends to be a little heavier than infantry armour.