I’m not an expert but it sounds like the force you need to apply to the plunger to push oil based testosterone through an extremely small opening creates high discharge pressure which damaged muscle or tissue. Also, the insulin syringe technique described here is for sub q injections, not intramuscular. That is why they pinch the skin, the drug goes under the skin but above the muscle basically. Insulin needles are not for intramuscular injections. Additionally, imo 5/8" needles are not long enough for injecting in your quads, i would go with 1" for quads and delts 25 or 23 guage. This is what I do with no issues.