Proof

The disappearance of body armor from the battlefield was from guns getting ever better and causing protection to get ungainly.

WFRP has guns in it, so I decided to see what I could get...

An Elizabethan musket is a BIG gun.  TL4 .80 Caliber smoothbore.

It'll do 4d+2 pi++.  Out to what we think of as pistol ranges today.

That will score an average hit of 16 and anything that penetrates gets doubled.

You need DR 26 to be immune.

Let's start with a TL4 heavy plate corselet with DR 9.  $4,000 and 32 lb.

The average hit penetrates.

But we can upgrade!

For $36,000 we can get our corselet to DR 10 and reduce it's weight to just 29.7 lb! using the duplex armor rules.  Fluting drops the weight to a mere 25.6 lb. for $52,000.

We can get to DR16 just by making the normal plate thicker.  $18,000 and 56.5 lb.  Using duplex armoring we can get to DR 16 for $162,000 and a "mere" 50.9 lb.  Fluting it as well drops the weight to 45.2 lb. but cranks the price to $234,000!

And that's just proof against average die roll.

DR 26 will weigh 272 lb. and cost $38,000.  Duplex and fluting to get the weight down is $494,000 but only gets it to 217.6 lb.

BUT!

WFRP is a fantasy setting and that means magic!

For a "mere" $131,200 we can cast Fortify on it five times for +5 to the DR.  That's DR 15 for our duplex and fluted heavy plate corselet.  DR 15, $183,200, 25.6 lb.  Starting with a thicker DR 10 corselet gets us DR 16 with enchantment, duplex and fluting for $209,200 and 38.4 lb.

For an extra $16,500 we can cut the weight of the armor in half with Lighten.

DR 15, $199,700, 12.8 lb.

DR 16, $225,700, 19.2 lb.

DR 26, $485,700, 83.2 lb.

Notice that enchantment is most cost effective than more steel!

Be cautious, that enchanted stuff doesn't work in low or no mana areas.

Getting the to work in low mana ups the prices to $240,012; $266,012 and $526,012 respectively.  Well worth it if you stumble into low mana areas.