Wow, an 18 gauge! I'm impressed. That's one hulking needle. I fill the syringe using an 18 gauge needle.....but being a softy, I change it out for a 23 gauge to inject.
believe it or not, i get much more pain from using small needles such as a 23 gauge or a 25 gauge than i do from an 18 gauge, especially if we are talking about glute injects.
i hate nothing in life more than shooting 3 CC out of a 25 gauge, and the process taking 15 minutes.
however, i love shooting with the 18 gauge. you control the speed that the oil comes out. obviously you should inject at a somewhat slow pace so the oil spreads or whatever bro science has dictated us to do, but i like that i can get a quick 1 cc shot in in under 1 second if i so choose.