Thread: tidy up crown on .22lr

I used a brass screw with a round slotted head from Mitre 10. I chose the size that was about twice as big as the bore. I think it could have been smaller. I checked the head of the screw for flaws such as burrs. All was well. I mounted the screw in my trusty Makita drill and selected the slow speed range. I pushed a bit of toilet paper into the muzzle to stop valve grinding paste getting inside the bore. I smeared some valve grinding paste onto the head of the screw and ran the head of the screw lightly on the bore of the muzzle of the rifle at a varying angle for a few seconds, lifted it and smeared the paste a bit and did this a few times until there was a bevel in the muzzle which went below the grooves of the rifling. It is essential to make sure that there is no bias of the screw/bore interface. So, shift the barrel to different positions to compensate for the probable bias in the way the electric drill is held to the muzzle. I checked for uneven result periodically with a bore scope. When the level was below the grooves of the rifling I changed to 600 grit diamond paste until the coarse scrapes of the valve grinding paste were gone and replaced by a smooth surface. It was an easy process. I didn't need the bore scope but I wanted to be sure that I was not creating a problem which was not visible to the naked eye. A magnifying loupe would have been quite enough to inspect the muzzle, and this is what I used for another couple of rifles. The valve grinding paste was not of good quality. It was imported from India and the only product in the auto shops. I don't recommend it (comes in a small tallish round tin). The grit size is not consistent. A coarser grade of diamond paste would have been ideal, before finishing with the 600 grit. The size of the screw head was a bit big and it took too long to create the bevel. A smaller head would have got there quicker. I bought a few different sizes and found that a small acorn-type brass nut on a screw worked better on other rifles. It all takes about half an hour, including clean up of the muzzle. I had a muzzle refaced at Gunworks later and they did a great job and it was not expensive. But I had to leave the rifle and then pick it up. Also, doing the job myself gave me some satisfaction. Don't use a stone of any kind. That would be brutal and may produce a muzzle/bore that is not symmetrical. Just gentle centering weight on the power drill/screw is all that is needed with regular refreshing of the grit. It is just like doing a valve grind but easier with the electric drill.