Testosterone makes a big difference. Average people have 500 ng/dl, but people who inject up to 3000 ng/dl have triple the muscle gains and even gain muscle without exercise.
See this image -
From this article -
Your 300 ng/dl is only 60% of what the average male 20-40 years old has. Improving would be beneficial.
okay and the guy with 3000 T levels for an extended period of time would also have blood like oil and die of a heart attack .. you cannot keep your levels that high for a long time or you will run into major health hazards