Got the recipe for the potion from Bobby. I've attached it below.
Witch Killing bullets are pretty easy to put together, but they can really turn the case around if you're up against a particularly nasty witch. Once you have all your ingredients (see pdf) then you just have to mix them up, and chant the correct spell.
We've found that both; "Ego voco impetu delere vos... coelum et infernum." or "Furor divina virtute in infernum eam detrude." seem to do the trick. Though we recommend you go with the first one.
Quick side note: Make sure the chicken feet are chilled and added at the very end right before chanting the words. Trust me. The spell won't work if they're not properly chilled. First time that happened to us, we had to Dr. Phil our way out of it with some good old fashioned witch marriage counselling.
Once you have the potion, it's potent for a long time. We haven't been able to fully determine the shelf-life of the potion or the bullets yet, but we always make sure to keep a batch ready.
You can choose to just use the potion as is, but it's a bit clunky to be carrying around a bottle all the time. Which is why we found a way to make witch killing bullets with it.
Once you have your witch killing brew, making the bullets is easy enough; all you need to do is fill a batch of hollow tip bullets with the brew and you're set.

Use:
The bullets can kill any witch, even stronger witches that are normally immune to bullets. However, they don't actually limit the powers of any witch, so make sure your first shot hits its target. The spell causes the witch to completely disintegrate in ash and blood, but with the bullets the witch'll just die as if hit with a normal bullet.
If you need any help with putting together your ingredient list, or creating your bullets. Let me know. I'm happy to help.

Witch Killing Brew.pdf
Thanks, mate, this will make my next witch hunt a million times easier!
This is... wild. To think I've been killing witches the hard way.
Thanks a lot for this, @S.W_Kansas_83. I'll definitely use this the next time I encounter a mangkukulam (well, that's what we call witches in my native language - just thought it's something I can share). Will share these to my other contacts, too.
Thanks son... Would ya say normal hollow tips work, or should they be silver?
If anyone needs help finding a particular ingredient, send me a message. I own two stores dealing in spells, potions, ingredients etc. I promise not to sabotage, as long as you promise not to kill me.
Thanks. The last witch I hunted turned me into my two year old self. As protection, you should try wearing the talisman of a head witch of a coven. Good luck.