Recently I did some experimenting with pinning oil based gear with slin pins.
I pinned my wife with a low dosage of test prop 100. Point 1ml in the delt. The equivilent of 10mgs. She is a mature adult and her levels were low. We had some blood work done prior to starting the therapy. Even tho it was a fast ester we went with 2 injections a week. I figured for a woman the levels would be stable enough. We did the treatment for 12 weeks and things work out great. She dropped bodyfat, libido went up, training intensity was there, and so were the visible gains. The pin was a standard 29awg 1/2 inch pin.
At the same time I pinned my training partner with a 29 awg 1/2 inch slin pin. His results were not so good. Within 3 days he developed a golf ball type of swelling that was bright red in his delt and according to him was extremely painful. His dose was a full cc of test prop 100. 1 ml in the delt. The equivilent of 100mgs. 48 hours after pinning that delt I pinned his other delt. Same reaction. After one week elapsed the redness, swelling and pain went away. After the site cleared we did the same product and amount but this time used a 23 awg 1 inch pin. The result was normal. No redness, swelling, or pain.
The female in this was 120 lbs with a body fat level of 14-17%. The male was 300 lbs with a body fat level of 25%. He is a power lifter not a body builder. I believe that if you are a smaller person you can get away with the slin pin but if you are a larger person that the oil does not go deep enough into the muscle to get absorbed properly and gets trapped in the space between the skin and muscle and becomes an irratant. It eventually did get absorbed but not being able to train as a result of the discomfort out weighed the comfort of the small needle. The moral is a little more pain from the bigger needle was better than the lesser pain of the small needle during injection with the one week of down time from the gym. This information may not be relevant to a seasoned veteren but I'm sure there are a lot of new guys thinking about the big needle vs the smaller needle. Good luck in getting to your goals.