I dont think it would be the pins. Not sure what the issue is. It could be a chance in solvents and your body is a little more irritate by this new batch, You can get some sterile oil to mix in the barrel with each shot, that will cut the pain, most of the time. I would start with a 1 to 1 ratio of sterile oil vs gear. Then in your next shots, see if you can use less sterile oil. You can also gently heat the gear up before injecting to lower viscosity. This will make it absorb faster. Just make sure it isn't hot, so that you don't get burnt while putting it into your body