expires_in max-age cache control doesn't work - ruby-on-rails

Question

I can't get the max-age cache control to work properly,
I have used expires_in that resulted in a "Cache-Control:max-age=86400, public, must-revalidate" header.
But yet, the browser still sends the request to the server, at least it is defined as "304 not modified", meaning that the ETag/If-None-Match headers works properly.
I have tested it with webrick on my localhost and on heroku,
with chrome 45 and Safari.
And no, my development tools are not opened, and the "disable cache" is not checked.
I also have tried to remove the ", must_revalidate: true" of the expires_in method call.
What am I missing?
Here is the output from the network in chrome:
General:
Remote Address:127.0.0.1:3000
Request URL:http://localtest.me:3000/api/books
Request Method:GET
Status Code:304 Not Modified
Response Headers:
Access-Control-Allow-Origin:*
Access-Control-Request-Method:*
Cache-Control:max-age=86400, public, must-revalidate
Connection:Keep-Alive
Date:Tue, 08 Sep 2015 13:28:01 GMT
Etag:W/"1f1b2d0b822830bc74e7c47a116205be"
Server:WEBrick/1.3.1 (Ruby/2.2.1/2015-02-26)
X-Content-Type-Options:nosniff
X-Frame-Options:SAMEORIGIN
X-Request-Id:c70d4715-dcff-4558-85af-9d21556d406a
X-Runtime:0.553353
X-Xss-Protection:1; mode=block
Request Headers:
Accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,/;q=0.8
Accept-Encoding:gzip, deflate, sdch
Accept-Language:en-US,en;q=0.8,fr;q=0.6,he;q=0.4
Cache-Control:max-age=0
Connection:keep-alive
Host:localtest.me:3000
If-None-Match:W/"1f1b2d0b822830bc74e7c47a116205be"
Upgrade-Insecure-Requests:1
User-Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.85 Safari/537.36
And here is the ruby code:
before_action :cache_control, only: [:index, :show]
def cache_control
expires_in 1.day, public: true, must_revalidate: true
end

Answer 1

Well, the headers are fine, it is just a meter of how browsers treats the reload button or shortcut keys.
I found the answer here: https://stackoverflow.com/a/16510707/789658
Here are the findings in chrome:
Pressing Enter on the address bar respects the "max-age" and doesn't send a request to the server.
The reload button or Cmd+R sends a request to the server with If-Modified-Since and will return 304 if resource wasn't modified since...
Cmd+Shift+R sends a request to the server without even If-Modified-Since