There are 2 things

- first 2 lines look good, but how do you switch between normal crouching and crouching with variable crosshairsize? There seems to be one bind missing that allows to change crouching modes.

- make sure you don't use space between '+' and 'movedown' or 'vstr'. +vstr and vstr are 2 different things but I think you know that.

Here's how I'd make it work, but can't test it right now:

set RD "+movedown; cg_crosshairSize 50"
set RD1 "-movedown; cg_crosshairSize 62"
set RD2 "set next_RD vstr RD3; bind space +movedown; echo Regular crouching"
set RD3 "set next_RD vstr RD2; bind space +vstr RD RD1; echo Small crosshair crouching"
set next_RD "vstr RD2"
bind SPACE "+vstr RD RD1"

bind key "vstr next_rd"

I'd also add variable cg_fov to that small crosshair crouching (if you don't use it at 90 all the time) to make it perfect:)