Changing the weight of bold text with CSS - not working!

So I am trying to customise the weight of the bold text on my portfolio site. I am using the attached lines of code.

When I input the weight value as 500, the text is no longer in bold. But when I input the text value as anything above 500 (in this example 600, but I have tested this with 501, 510, with the same results), the text is very bold. It doesn't increase incrementally, it just seems to only have two settings. I know that Halyard (the typeface I'm using) has a range of weights to choose from so it's not a problem of actual availability of a range of 'boldness' of the typeface itself.

Am I making a mistake? Is there some sort of code I can write where when I make a bit of text bold, it makes it a custom font, and then just insert that font as a slightly bolder Halyard? 

I hope that makes sense! Thank you for reading and for any help, I really appreciate it! 

Maybe the font doesn't support this weight.

Can you share link to page where you use text?