Use alcohol to make up a thin white syrup, then dip the part of the bullet that protrudes on your existing rounds.  It is not totally covered, but the coated part leads the uncovered portion into the barrel and it will establish the rubbed in place barrel condition after a bit.

As good as impact coating the entire bullet?   No.  It is a wash coating, and it is not beaten into the metal.  The part in the neck is still raw un-lubed copper jacket.

Would it help cold shots and barrel life?  Yes, to a degree.

Would it slow down the pre-built existing rounds some.  Yes.

I just put together another 30 round exploratory series, containing 150 grain and 160 grain slugs fully impact coated and at 48 grains, 49 grains and 50 grains of R19.

Also rebuilt my chrony to replace the damaged arm that got shot off at your house (by me of course) so I can put the glare shields back on so I can get a higher rate of read off the thing again.   The "hit or miss" rate on the fps readings I was getting was excessive, with more errors than good reads, so I think I needed my glare shields back in place again.

Fixing the Chrony was required, as it would be my luck to be all excited over "progress" that is simply a sick crony kidding me along.

Got ammo builds that I have chrony data on to use as a back check, they were ones we did at your house BTW.