Century Arms C308 basic forearm options . Cetme G3 HK91

Well lets start with what fits:

 Replacing forearms " front handgaurd " may require a little fitting like some sanding , filing or a Dremel maybe handy if it was desighned for the HK G3 or HK91  .

Cetme rifle sight bases " triple trees " have a raised ridge that fits under the forearm the HK91 does not. As you can see the ridge has been removed from  the sight base on the right side to allow a better fit  . I find it easier and preferable to remove material from the forearm to make them fit .

Early Cetme rifles used a ventilated sheet metal forearm
 with a built in Bipod like the one  pictured above.
They are a bit uncommon but I'm sure if a person looks they can find one .

Wood forearms are available and were used on the Cetme, G3 and HK91 .
 There seems to be several variations .
The Cetme forearms seem to be retained buy a screw that passes through the front of the front of the forearm and HK types seem to use push pins .  They are pretty easy to get a hold of but condition varies along with the price . 

Century Arms C308's have came with Plastic Forearms based On the G3/HK91 slim forearms but they are not a perfect copy . The number one difference is they lack a internal metal heat shield and tend to heat up faster during sustained fire.

The G3 plastic slim forearms are available in pretty good shape for very low prices in a variety of colors and are therefore a great way to change the Look of your C308 without spending a lot of money .

G3 wide forearm with bipod popular and expensive .