It's conventional double rifle wisdom one must shoot the left barrel first on a side by side double rifle for regulation to work.

I agree this is how they are made to regulate. But some double rifles seem fine with either barrel first.

Test yours out.

Shoot the normal sequence, 1,2. Then repeat.

Then reverse the sequence, 2,1 and 2,1.

Note, record, photograph, report back.

As many DRs as possible.