Mag timing

Got a weird one. Screw Hemi with grid and 44 mag, with Spud mag/trigger switch.
Set mag at 25 like I normally do statically.
Started on crank trigger - perfect at 25 on timing gun
Switch over to mag - big flames out exhaust.
Ran mag on its own - same and could not adjust timing to 25
Changed mag - same
Am here missing something?
PC