That tool is crap.
Take a sacrificial case and use a dremel tool to make a slit down to the neck/shoulder junction. Finger seat a bullet and chamber the round a couple times. Done.
If you don't have a dremel, then size the case just enough to catch the very rim of the case mouth and proceed as above.
This is almost, how I use to do it, also. 3 months ago I acquired the 21centruy expanding mandrel kit for my 6.5CM.
I use a Fire Formed case.
I anneal The case.
I use a Redding Body die to reset just just below the shoulder about a Thou.
I bump the shoulder back 2 thou.
Then I use a lee collect die to collect the neck down about .2620.
I then use the .2650 expander to expand the case neck out. "Slowly when expanding anything."
Depending on the case that you use, I use Lapua, with annealing, the bullet has just enough tension to slide with out any unwanted slipping or binding in the case neck.
I seat the bullet Long. I remove the bolt from the rifle. Insert the bullet in the chamber and push it forward into the chamber. I use a wooden dial about a foot long that fits the action of my Howa to push the case into the final position into the rifle lands. DO NOT push hard, you can feel the bullet seating itself in the lands. Once my shoulder has bottomed out in the chamber, I remove the wooden dial and take my BoreStick with a jag on the end and insert from the muzzled end and very lightly push the bullet point backwards.. The cartridge will easily move backwards with out the bullet sliding back into the case, 98% of the time , if you take your time, Fineness is your friend. After the cartridge is out of the rifle I am looking for LIGHT, LAND MARKS on the tip of the bullet, Not hard gouges cut into the bullet tip. That defeats the purpose. Then I take a measurement with my Hornady Ogive comparator "CBTO" and a measurement from the tip of the bullet to the base, "OAL". I Repeat this three times because I'm OCD and If I'm Lucky, so Far, my numbers come out the same every time. Then I subtract 20 or 30 thousandths and start my seating test from there.
This sounds like a lot, But it's not. This is how I prep my brass for loading except my final expanding mandrel is
.2620, not .2650. All I'll say from here is. This is how I do It and it works for me. I had to figure out other usages for that expensive Kit from 21Centrury. They could of at least put it in BIG LETTERS that the Mandrel Die was not included in the KIT. Yep I didn't read the small print.. Yes I had to turn around and order the expanding die. LOL