basically yea. i dont have time to make a elegant solution right now since i need to get to work but ill post a little description of what needs to be done so maybe it will put you on the right path.
basically you need to create a variable in your projectile that will be the initial speed, make this variable public/ editable and check expose on spawn. this way you can set the variables value when its created from the spawn actor node(see picture below). then you need a script in your construction script that sets the inital speed of the projectile movement component to the value of the variable.
then you need to get a way to reference the widget from the player so that we can use the sliders value to modulate a max speed value. i did this here by getting the widget in the hud then getting the slider component then get the value.
i would explain in greater detail but like i said im late for work haha
