I have been fighting Missouri 44 Elmer K Hi-Tek ever since I bought them. They too are 18 hardness and it does not matter what I do with them, they lead. Where in the barrel and how much depends on how hard I'm driving them, but I have been completely unsuccessful in getting the stop leading completely. On the other hand, their 12 hardness "cowboy #3" work perfectly.

I asked for advice on many forums and the overall thought is...they're too small in dia for my super redhawk, and too hard. Fixing either of those issues would probably fix the issue...sadly, Missouri doesn't give the option to get them in a larger dia, so I have to go softer, thus the CB #3.

Sadly, I'm mostly just out the $$ I spent on the harder ones...but you live, you learn.

I've used that exact bullet - without the hi tek coating.
Mine were .430" and I coated them with 45-45-10 before I loaded any. They don't lead my revolver and I run them at 1250fps.
If I could have the cylinder throats opened up, I would've tried to order .431" and skip the 45-45-10. But nobody seems to want to touch titanium.

Had horrible luck with coated bullets in most calibers at higher velocity. Tried many combinations. Poor accuracy(25 yard bench rested not 10 or 15 yard plinking) and much leading/coating residue. MB’s, acme and others. Lower velocities under 900 FPS and I got decent results. Keep Velocity low and results will be decent

My first try with coated bullets was a 125gr RN for my C9 3.5" 9mm pistol.

I had .356, ,357 and .358 dia. bullets shipped to me to test.
The .358 dia. did not fit my chamber........

but with several powders and a OAL from 1.06 to 1.16" I got this bullet from 938fps up to 1173fps.

I did not have any leading with this Eggleston coated bullet.

One just needs a good quality coating and a fit that is close to the barrel, for a good load........... maybe?