Get 26 or 27 gauge needles with a 1ml syringe. They wont be marked with international units and it will be a lot easier.
Using a narrow 1ml syringe over a 3ml syringe allows the viscous oil to flow easier.
Sub-Q can work perfectly fine.
Source:
Pharmacokinetic Profile of Subcutaneous Testosterone Enanthate Delivered via a Novel , Prefilled Single-Use Autoinjector: A Phase II Study