You're correct, 9v. It's been so long since I have needed to change batteries, I just had old man brain farts. I would toss the included 9v to the side and either use a new 9v or spring for the 123's. I never place any faith in included batteries.
You're comment on a slug skirting the end of the blade is an indication that the blade is not properly tightened down. I initially had problems mounting the blade on my Donnyfl. After fiddling with it for awhile, I discovered that the machining in the ldc prevented the base of the blade from being flatly mounted. Switched out ldc with the stock FX one and the blade mounted up perfectly. Put the Donny back on, moved the blade slightly forward of the machining, and problem was solved.
The best way to ensure proper clearance and alignment is to use a long wooden dowel inserted into the barrel. The dowel will give you a visual representation of the projectile leaving the barrel. You now have an easy way to ensure the blade is horizontally level with the bore and the clearance is properly maintained to the tip of the blade. I have shot 10's of thousands of rounds across my blade using this method and have never once clipped the blade. That's firing everything from my 5.56/7.62 rifles all the way up to using my .338 Lapua Mag rifle. Use this method and I guarantee you will never hit the blade again.
So quick recap. Mount base on flat surface of barrel/ldc. Tighten the living poop out of it. Use dowel to verify horizontal alignment and clearance of the blade. Shoot and be happy!
Oh poop, one more thing I just remembered. Check the left/right axis of the blade to the dowel. If I remember correctly, my blade would point slightly off axis to the right. I was able to straighten it out by simply applying a little pressure and bending it perfectly straight in line with the dowel. This is very important as there are two magnetic fields that the projectile will pass through. The first field is by the blast shield with the second field being towards the end of the blade. If the end of the blade is not in line with the dowel (projectile path), the blade will fail to register the flight of the projectile and won't read correctly.
I know that is a lot of info to digest. And I'm sure I am missing something. But hopefully this will get you squared away. At the very least, you will be able to scratch these things off the trouble shooting list.
p.s. Use the included micro sd card. TRUST ME!