318 Magnum first fire...timing?

Definitely 180 degrees out of time. I had the exact same backfire 2 weeks ago on my first start. I was sure I had #1 on the compression stroke, but didn't actually test it with my thumb. Once I did that, pulled the cap and the rotor was pointing to the back, pulled it out and rotated it 180 degrees to point to #1 and she started up just fine.