Crown Fix

[dtknowles]

I thought the crown on my Ruger #3 might have been a problem with the gun accuracy. It had a big spiral tool mark from the OD to the crown. I used a lapping plate and sandpaper to take it down and polish it. I got rid of the tooling mark but I might have stopped too soon as I left most of the original crown. Judging from the lube star it is not perfect yet.

126137

The two bright spots are from threads of a cloth, I was going to wipe it before I got the idea to take the picture.

Tim

[country gent]

A brass ball and some of that lapping compound will clean up the crown as long as it not a major ding. In a bind a brass round head screw can be used also. If the #3 is a 223 then a fmj 45 bullet would work too.

[dtknowles]

A brass ball and some of that lapping compound will clean up the crown as long as it not a major ding. In a bind a brass round head screw can be used also. If the #3 is a 223 then a fmj 45 bullet would work too.

I have looked really close and I don't see a ding or even anything untoward. It is more of a .224, it is a .22 Hornet. I might give it a go with the 45 fmj, Do you think that is better than a 40 or a 9mm?

Tim

[GBertolet]

I have had good luck using jacketed bullets of proper diameter, coated with lapping compound, to finish up a crown job.

[country gent]

All will work you want a smooth even true transition from rifling to face. The 40 and 9mms will make a deeper angle due to radious being smaller due to smaller dia. Another little trick is to coat the muzzle and existing crown with black marker allowing you to see the "cut" made. This also will show any low spots or poor form when starting cutting. On my match rifles that had to be cleaned from the muzzle ( Garand M1A) I would lightly touch up the crown every year right before the nationals. If you have them start with an automotive valve grinding compound and then a finer grit to flitz or simichrome polish.

[Ballistics in Scotland]

I have looked really close and I don't see a ding or even anything untoward. It is more of a .224, it is a .22 Hornet. I might give it a go with the 45 fmj, Do you think that is better than a 40 or a 9mm?

Tim

I think it would be. You really need something round and well over bore diameter, so that you can move its axis of rotation around as well, and avoid cutting a groove in the lapping object. If that happens, you can actually lap a tiny bell-mouth in the bore.


Even though it can be time-consuming, I wouldn't use a hand-held electric drill for this. The moving rotor is rarely perfectly balanced, and this can cause it to cut off centre, and your hole in the rear of a bullet may not be perfectly centred either. An electric screwdriver, being slower, should make the tool follow the lap or cutting burr, rather than the other way about.

[sbowers]

One of the very best things I have ever found for touching up a crown is a small round ceramic stone like those is in the mini grinders (dremel ect.). Use it by hand it is quick and works like a charm. I use it before matches on my Winchester 52's.
Steve