I figured i'd share this information that helped me get through the extreme pip i had with some over concentrated gear. I constantly see posts and questions about dealing with this, so heres the information that helped me.

What causes (non infection related) injection pain?

first the shorter the ester, the higher the melting point
secind, the concentration of the gear.
third, the solvents used.
fourth, injecting too quickly
fifth, virgin muscle.

Pain is caused when the oil/solvents are absorbed by the body and crystals are left behind.
Short esters (propionate or acetate) are harder, more painful crystals with melting points in the 100c range.
A hormone with a longer esters (excluding cypionate - cyp is long but also high melting point) can have a melting point in the 20c-40c range. not far off from human body temp.

Pain is also caused by concentration of your gear.
Building off of point 1: Let's say it takes the body 24 hours to absorb 1mL of a certain oil/solvent blend, and 24 hours to absorb 50mg of Testosterone Propionate. If 50mg (or less) of testosterone propionate is in 1mL of that oil, this injection should be painless. On the other hand, if 100mg of testosterone propionate is in that same 1mL of solution, then after 24 hours the body will have absorbed 50mg and 1mL, leaving 50mg behind in the injection area, crystalized and painful.
Its better to shoot 3mL of 50mg/mL Testosterone Propionate than 1mL of 150mg/mL Testosterone Propionate.
This is also why water based suspensions (Testosterone base/no ester, Winstrol ) hurt the most, water is very easily absorbed in the body

The solvents used can cause pain in 2 ways. Benzyl alcohol (BA) is used at 1%-2% as a preservative and antiseptic. If the alcohol content is too high the gear will burn. Pain in the first 24 hours is usually caused by heavy solvents, pain in the next few hours is usually cause by crystalization. Another way is a bad recipe. if someone used 2% BA, and the rest of the solution oil, the mg/mL would have to be low due to oil's weak ability to hold crystals. On the other hand, a recipe like 2% BA, 5% Guaiacol (super solvent), 10% Benzyl Salicylate (liquid asprin) with the filler split 50:50 between Ethyl Oleate (oil/solvent hybrid) and normal oil should be far less painful.

If you inject too quickly it can tear tissue.

If your muscle is new to the hormone, it will absorb the hormone very slowly, but absorb the oil/solvent very quickly. This will cause more crystalization and pain. As your muscles recognize the hormones, they will be absorbed more quickly, thus less pain. The deeper you inject into the center of a muscle group, the better.

How do I prevent pain before I inject?

Cut your shots 50:50 with sterile filtered oil. If you want to use 50mg of Testosterone Propionate, and you have 100mg/mL Testosterone Propionate- pull 0.5mL of your test prop, and 0.5mL of sterile filtered oil to shoot 1mL of 50mg/mL Testosterone Propionate. This is the #1 best way.
Dont bother with b-12, its water based- absorbed so quickly it will have little to no impact.

Before you shoot, it can help to warm your gear some (especially suspensions). You could put the vial in the bathroom sink and let hot water run over the vial for 2 minutes, and shake well. This will lower the oils viscosity also making it easier it pull into the syringe.

Inject slowly, take 30 seconds per mL. Use a 25g pin to inject so it forces you to move slowly.

If none of these work you could have dirty gear. Its possible there could be particles (although bacteriostatic) in the gear that are not causing infection, but still cause in site infection that made it through a filter.

How do I deal with pain once I have it?

The worst thing you can do is ice it. Cold will help the crystals fall out of solution/suspension.
Its okay to take some ibuprofin to decrease the swelling, and help with pain.
Also being in a hot tub, or jacuzzi, or warm bubble bath will help melt the crystals down. Using a heating pad can help also.