View Full Version : can i use this to crown the barrel of my 8mm mauser?
March 30, 2009, 09:01 PM
okay im in the proccess of turning a turk into a sporter. i have heard of using hand tools to crown a barrel. is this what there talking about?
March 30, 2009, 09:05 PM
Use a tool like this one (http://www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=855&title=POWER%20CUSTOM%20BRASS%20MUZZLE%20CROWNING%20LAP). I've done it with a marble and valve grinding compound.
March 30, 2009, 09:21 PM
Please don't use that tool to try to recrown your barrel. There is a tool put out by brownells that looks similar to that but it uses pilots to ensure the tool is concentric to the bore.
I've also used the lapping tool the other poster linked to. It does a pretty good job but there is no substitute to a dialed in barrel in a lathe.
March 30, 2009, 09:31 PM
okay now i understand a little bit more. but do i just use that lapping tool or do i have to use somthing else to get it started? (i am cutting down the barrel not repairing a original crown.)
March 30, 2009, 09:51 PM
Years ago I crowned a barrel with a hand crank drill, valve grinding compound, and a couple of really big roundhead bolts.
You'll also need a very fine file to break the burr that's left inside the barrel after you're done.
March 31, 2009, 10:32 AM
A lathe and crowning cutter is the best way to do it, but if your like most table top gunsmiths, you work with what you have.
The round head brass bolt trick works very well. You want the end of the barrel to be a perfect 90* when you start. Like mike said, look for any burrs after you have finished it. Use a q-tip on the end, the burrs snag the cotton.
March 31, 2009, 11:25 AM
I don't think I'd use the tool linked by the OP. It's just a countersink and will not result in a concentric cut. Some of the other methods seem OK, if a bit time consuming.
March 31, 2009, 11:55 AM
I figure it took me about 4 hours to do a credible crowning job.
It was an old rifle that belonged to a friend that had a badly mangled crown. He didn't know how it happened, it was like that when he bought it. It looked like someone had gone after it with a tire iron.
Anyway, we cut the barrel back by several inches with an electric hacksaw and went from there.
I figure it took about 4 hours total time to get it crowned, polished, and the burrs relieved.
It simply wouldn't group before we shot it. Literally shots all over, at 50 yards groups were at least 2 feet.
After crowning we shot a couple of quick 3" groups over iron sights. He later put peep sights on it and turned it into a credible 1" at 100 yards rifle.
March 31, 2009, 11:59 AM
You want to take it in two steps, IMHO. First you want to cut the barrel off square. Otherwise a lap will not work the edges equally, and that results in uneven muzzle gas ejection following bullet exit, and that tips the bullet and can spoil accuracy rather dramatically in some cases. A square cut is most easily done in a lathe because the muzzle doesn't need to be centered to get a true 90° cut. You just chuck the muzzle in a 3 jaw chuck and run the parting tool straight in with the cross slide.
If you don't have that available, the next best thing is a piloted square end cutter like this one (http://www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=18289&title=90\%20MUZZLE%20FACING%20CUTTER%20&%20STEEL%20PILOT). It takes some skill not to let it chatter. Use plenty of oil and cut lightly. Take your time.
If you can't afford that, you will need to true the cut with a file or a scraper. If the barrel has the usual straight military contour, just laying a square against it and filing the high spots it touches until it is even all around will do it. M.L. McPherson has been known to do this at the range, and draw stares, while he shortens a barrel to find a sweet spot.
Another method of squaring a barrel end will get you surprisingly close. Again, this is for a straight contour military barrel. You put a post level on the barrel and clamp it straight up and down. Put a circular bubble level on your file and file very slowly and carefully, keeping level. Walking around the barrel helps even out your errors. Check the post level periodically for shift, and don't forget to plug the barrel with a wad of tissue to keep the filings out.
Once you have a trued end on the barrel, you can lap it. Rather than buy a lap I prefer to make one. You can download instructions in PDF format from my file repository (http://drop.io/unclenick). If you buy the crown 90° cutter, you can get cutters with other degrees of taper to finish the crown with. I own them but prefer the lap, as it is self-centering.
March 31, 2009, 12:22 PM
A square cut is most easily done in a lathe because the muzzle doesn't need to be centered to get a true 90° cut. One could certainly cut a muzzle out of square using a 3-jaw chuck. Gotta be careful with that. Uniform runout along the chuck's axis is OK, but if the muzzle end is describing one circle in space and the breech end is describing another circle that's not concentric to that one, you won't be cutting perpendicular to the bore. I don't know how close to perpendicular the end of a barrel need to be to cut a proper crown, but I personally would indicate the barrel to run within a couple thousandths of an inch.
March 31, 2009, 12:27 PM
If you are going to recut it you will need a tool to recut the crown, a lapping tool just to clean it up.
The tools need a guide that enters the bore to keep the tool aligned properly and not damage the bore or you will not get the best from the barrel.
Read a lot about what to do and how to do it before preceding with this operation.
March 31, 2009, 01:00 PM
Using a round bolt head or a countersink (the tool shown by the OP) can cut the crown unevenly; you need the crowning/champfering tool with a guide.
The neatest tool I have seen, which works with a lathe having a hollow headstock, is a tool ground in a shallow "U" shape. It is set up so the tool is parallel to the barrel and then moved straight into the crown, cutting, smoothing and facing all at one pass. The shop needs several for different barrel thicknesses.
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