Very high, 50% in some cases Headshots per round. i know that he has 4000+ hours but.. 

Ill just pick a few

35 from 65 kill were headshot kills

http://battlelog.battlefield.com/bf4/battlereport/show/1/952555224800564224/363483517/

21 from 66 kill were headshot kills

http://battlelog.battlefield.com/bf4/battlereport/show/1/952285723433086336/363483517/

21 from 46 kills were headshot kills 

http://battlelog.battlefield.com/bf4/battlereport/show/1/951883096064708160/363483517/

18 from 34 kills were headshot kills 

http://battlelog.battlefield.com/bf4/battlereport/show/1/948690781596005312/363483517

As you can see from the link below this is a regular thing high HSK per round

http://bf4cheatreport.com/?pid=&uid=LittleG78&cnt=200&start=&startdate=

The overall stats show an overall higher headshot rate, so these reports seem to be possible for this player. I do not see significant evidence for cheating.

https://bf4db.com/forum/thread/littleg78-is-hacker-aimbot-hs-4169