If your looking for a lite spring for 300 blkout this may be it. - GUNTEC USA AR-15/AR-10 Adjustable Flat Flex Chrome Stock Spring

If you have ever used any other flat springs you will know this is junk. First off its short for a flat spring at about the same length as a regular carbine spring. It provided no benifits to using a carbine round spring and in most cases ended up overgassed in my ar15 16" As for ar10? Good luck not beating up your gun. I originally bough this spring to replace the stock spring in my 308 16" and ended up using this spring in my 300blk 8 1/2" barrel where it does ok. Time will tell if it has enough to cycle the gun when it gets dirty.