The BA isn't higher in 400 to hold it in solution. It would be the BB.... BA is used as a preservative to inhibit the growth of bacteria in the vial. 2% or 3% BA in a vial is plenty and that is the same for 250 test or 400. It is the amount of BB used that is different. 0-15% BB used with Enanthate to hold 250 in solution but I use 20% BB to hold 400 in solution.
The reason for the burn is not the Chemicals used BB or BA, the reason is the super saturated concentration of Test powders crammed into one little vial! This is just so much in one area that the body's inflammation reaction takes over and is forming an abscess around the compound because it is in too concentrated of a dose! Adding the deca (which is not as reactive to the body's inflammation process) dilutes the solution of test down to a bearable level.
You can take 1cc of the 400 and draw it up into a pin and then 3/4 cc of GSO (sterile) and run it under hot water for a bit, flick it around and then pin it and you will be fine but you might as well be buying two bottles of test 200 and shooting 2cc a shot..... same thing!!!
Test 400 is for ppl whose bodies have become resistant to extreme doses of test per week and even still then, alot of guys experience knots and inflammation.
Chemist