welcome to MC.
And it all depends on brand , as 300mg sustanon sounds like an under ground lab to me. I have only seen 250mg sustanon which doesnt hurt too bad when made by organon or Jelfa, but i dont know of any 300mg 4 ester sustanon
Also sustanon is suppose to be 2 short 2 long ester and now days guys call all kinds of stuff sustanon lmao, so everything is relative i suppose