Look, 400mg/ml no matter how you make it will make you sore if it is dosed correctly. Chances are, if it si a single ester or double like cyp and E, it is under dosed. You can make 300mg of test e or c painless but not 400. And if it has any prop, or phenprop, it is going to hurt.
And 600mg.ml, BS, unless it is made with some solvent that is not suppose to be used in humans.
And it is not the alcohol content that always causes the pain. With high concentrations, the oil and solvents will be absorbed faster than the compound leaving crystal knots that cause a lot of inflammation. I've seen 75mg TP, 75mg TPP, and 250mg Test E made with 2% BA, 18%BB, and all EO and it hurts. Some times you will get a relatively sore less shot, but others are very painful.
I doubt 600mg would even hold in 100% EO even with BA as High as 5% and BB at 20%+. There are chemicals that will allow it to dissolve, but they are not meant for human use as they are toxic.