Would it be correct to assume arming took place after so many fin section rotations?
No. There were two elements that initial impulse rotated into position, aligning the striker with the detonator. The delay allowed the round to get 5 meters beyond the muzzle before it was fully armed.
I have fired about 150 FRAG-12 rounds, so it’s safe to the firer.
We ran a test where we fired about 20 rounds at a medium-sized car and they tore the heck out of it and at midway through, the gas tank went up.
We had a fire truck standing by for just such an outcome. Completely destroyed the intake manifold of the engine and blew big holes through the windshield, showering the plywood dummies inside with fragments.