Tuning Which abrasive to use for "brass screw" crown job

I've used mediun valve lapping compuond with good results. Inexpensive and easily obtained at your local auto parts store.

I use JB Bore paste followed by Flitz,just as I do for the actual bore of the barrel. Hope this helps You.

Mike.

I use “Clover “ medium grinding compound in the green metal can that I have used for decades. Permatex makes some in a tube for about $5.00. Most grinding compounds are made of silicone carbide dust captured in a grease. Hope this helps. MM

For the first timer, just be aware there isn’t a specific abrasive you have to use. Any of the above suggestions are fine. You’ve seen close ups of a proper crown with a neat bevel revealing the distinct profile of the lands and grooves. So just start slow and monitor your work, and if it looks like it’s removing material too fast, back off and use something less aggressive. Or if it’s going very slowly, move to something more aggressive. Better to err to the side of going too slowly though. For example, I find J-B to be too slow by itself so I mix it into a slurry with a medium polishing compound…the stuff you buy in stick form to load onto a polishing wheel (Porter Cable #2 in my case). Once I’ve established the bevel, I wipe it clean and do a run with J-B bore compound and then finish up with J-B bore bright.

As I mentioned in my little accurizing guide, the most common mistake I see is where someone uses too much pressure and pushes a very slight burr into the bore. It may not be visible with a 5x loupe, for example, but you can feel it as a slight hitch just as the pellet’s head gets there. The old saying “go slowly and let the abrasive do the work” holds true. I limit the pressure to something less than probably 2 pounds.

An example I posted a few days ago:

NICE looking crown!

I'll second that^

I have been guilty of burring a crown before. Wayyyy more than 2lbs of pressure was used

To test for any burrs use a Q-Tip. Any burrs will latch on to cotton fibers.

Provided it is an unchoked barrel, I recommend pushing a few pellets through. You will pick up a subtle burr that won’t snag a cotton swab.

Doesn’t work on a choked barrel though because you’re already overcoming a restriction.

But for sure it’s bad if it grabs cotton fibers.