I've been heating gear in the micro for years. Just unscrew the pin, stand it up in a coffe cup, blast for 30 secs, screw pin back on, mix a bit so it's evenly distributed, then shoot. Even if you don't have full blown scar tissue repeated injects does toughen up the muscle a bit. Besides, warm oil disappates better when you massage it in the muscle and it's less likely to cause pain and swelling with hot gear like prop.