Shredded patch

[Zonie]

M.D.
The way I read your comments, you are talking about working on a barrel that does not have a crown formed yet.

I agree that using a lathe or the round ball with an abrasive is the way to go in this case.

I am talking about finished barrels on factory made guns where the crown has already been machined.
The factories don't take the time to dull the rifling where it meets the finished crown. They just deburr it by removing the hanging burrs, blue it and assemble it.

In cases like this, using my method does not "form the crown". In fact, the only material it removes are the sharp edges where the rifling meets the factory crown.

Now, if there is no crown at all, like one finds on some new barrels, that's a horse of a different color and as I said, I agree with your methods for dealing with that problem.

 

[Hylander]

Nice shooting,
The GPR's are good shootin' Iron's

 

[Elkeater]

And I agree with the "rounded" land edges in the bore. I mean, that's what one gets with radius groove rifling; right? That way, no cut patch.
[/quote]

I'm going off topic Hanshi, what's new?
I thought radius groove was the bottom inside corners rounded; the top outside corners still sharp. Or is every corner rounded?
I suppose this may be specific to each barrel maker. :idunno:

 

[SgtMaj65]

:thumbsup: :hatsoff:

 

[Grenadier1758]

Only the bottom of the grooves are rounded. The edges of the lands can be sharp. You want the muzzle edge of the lands to cure lightly toward the muzzle or what is sometimes called a crown. Sharp edges at the muzzle cut patches and contribute to shredding of the patch.

 

[M. De Land]

I guess I have totally failed to convey my thinking.
Let me try again.
I cut the crown in the lathe with tool bits shaped for such work that leave the land and groove edges on a radius but with tool marks that need to be removed and the profiles maintained. A ball shape does this the very best because it maintains all the radial and land corner integrity cut there by the lathe bit.
Sanding these areas off with a back and forth rotation by your thumb rounds off both the radial chamfer integrity and corner profile of each land in a random, inconsistent profile that can easily be seen in a magnification comparison. It ruins the crisp radial shape the lathe tool bit formed on the edge and two corners of each land.
When a thumb is used to do this in a back and forth rotational method the land end radius and the land end corners are rounded off inconsistently both radially and over the end.
A ball maintains the radial cut as well as both corners of each land in a consistent shape, profile and depth. Your thumb will round off both inconsistently.
The other draw back is that the emery paper bend over from your soft thumb will often scratch the land tops in the bore in back of the edge your working on.
Use of the thumb for this job is very poor practice for crown profile but will certainly round things enough to stop patch cutting.

 

[Rifleman1776]

A ball maintains the radial cut as well as both corners of each land in a consistent shape, profile and depth.

Exactly. As a machinist you understand that. For us lesser gifted tinkerers the use of a large (enough) brass round head bolt or screw will work just dandy. Some lapping compound is, of course, called for. Can be done with a hand drill, fancy tools not required.

 

[Gene L]

I've read on a target website (centerfire) that you can use a brass round headed screw with lapping compound to recrown a barrel. Chuck up the screw in a hand drill.

I've never done this myself, but I don't see why it wouldn't work. So long as you maintain a 90-degree angle to the muzzle.

Finding a round-headed screw that will work for a .54 might be problematical.

 

[Griz44Mag]

I've read on a target website (centerfire) that you can use a brass round headed screw with lapping compound to recrown a barrel. Chuck up the screw in a hand drill.

I've never done this myself, but I don't see why it wouldn't work. So long as you maintain a 90-degree angle to the muzzle.

Finding a round-headed screw that will work for a .54 might be problematical.

I have used a large carriage bolt. Smooth head, shaft will fit in a 1/2" drill chuck.

 

[Jimbo47]

There is no argument that a screw head, (if you could find one large enough) or round ball object using emory cloth, lapping compound on a drill, would be suitable, but as someone mentioned at the beginning that started the whole debate, was about using a thumb and emory cloth, or sand paper to smooth out the muzzle.
I usually take caution in trying anything mentioned on a forum as fact, without at least some debate to it's merit.

 

[M. De Land]

That is sound advice. The thing to do is check some good gunsmith reference books for how the procedure is done and you will still get different opinions but it will be more fact based from those who actually do the work for a living.
I like and use two books quite often for reference material, one of my favorite authors for general gunsmithing is Roy Dunlap. Another very good reference book,set of two, for very technical stuff is Howe. This set covers stuff like rifling cutters, reamer building and hand lapping of barrels.
Smiths book of Harry Popes barrels is another excellent resource on barrel manufacture evolution. This book somewhat transitions barrel making alloys and techniques from forge welding and Damascus to deep hole boring,reaming and rifling of moderns steel, which is what we use today.
Then there is stuff you just learn by doing the work your self. I have changed much of what I learned about lapping a barrel from gun school and Howe's books on the subject by trial and error.

 

[hanshi]

In my post, I did not aim to infer that the lands on radius rifled barrels were themselves rounded. Rounded, they are not but they do come close. I have two radius groove barrels from Rice. Close comparison with, say, my square cut rifled GM barrel shows a marked difference. Rice radius barrels (maybe others) are polished and rarely, if ever, have sharp edges. Due to the very nature of this type rifling, rather than a sharp edge on the land corner, the land corners are smoothed over much like the description of the relieved crown now under discussion. Hopefully, this will clarify my point.

 

[Rifleman1776]

Finding a round-headed screw that will work for a .54 might be problematical.

He is a machinist and an ml'er. I'll betcha he has a bunch of 'stuff' around his shop that he can scrounge from. A .60 cal. lead round ball with a screw in it will work fine.

 

[M. De Land]

I personally mix up muzzle finishing tools and techniques according to muzzle size and crown shapes but always prefer to do the work while still set up in the lathe because of the added accuracy potential to keep every thing square and true to the cut profile.
A ball is particularly effect when doing this by hand out of the lathe because the shape is self correcting and safe to the cut profiles on the land and groove corners and edges.

 

[Zonie]

Again, your talking about forming the overall shape of the crown.

As a machinist, you should know that the cutting tool that forms the crown will leave sharp edges on both sides of each rifling groove where they meet the crown. This is less true with the edges of the lands of the bore as it meets the crown.

IMO, it is these sharp edges of the rifling grooves that can cut a cloth patch as it is loaded and I feel that each of these edges need to be dulled to prevent this from happening.

This is where using metal cutting sandpaper like the black silicone carbide paper and a soft backup like a thumb can solve the problem.

Trust me folks. It works very well without changing the angle or shape or centrality of the crown.

 

[M. De Land]

No, the crowning tool cuts the radius to the bottom of the grooves so that the end of the lands and chamfer at the bottom of the groove are in the same arc. All the emery paper does is clean up the tool marks.
The method you described messes up these machine cut profiles at the leading and trailing corner of each land rounding off the radius edge between them. I'm talking about rounding radially corner to corner not over the edge of the land end. The idea to get best accuracy is to make all these exit areas crisp and uniform, blended together so the ball can exit precisely the same each time.
A crown so cut and finished will produce the best accuracy the barrel is capable of with ball our bullet.

 

[M. De Land]

This is a good example of what I am talking about.
I cut this crown well over 30 years ago and it is still pristine and sharp as the day I cut it after many thousands of competitive shots through it.
Note how the bottom of the grooves and the end of the lands are all in the same arc radius. The lead land corners are the same shape and profile of the trailing land corners. This consistency cannot happen with your thumb under some emery cloth twisting back and forth to form a crown.
It loads smoothly and is a very accurate .54 Douglas barrel. Probably 12L14 so I don't hot rod it .
This is my favorite crowning tool that has been used since I opened the shop in 1980. It has cut many,many barrel crowns of all shapes and sizes. You can see it has been sharpened many times.


A muzzle is first faced off square with the crown tool from the end of the hook point then the outer perimeter is usually given a chamfer on the flat corners and edges with a stone. After that the bore chamfer is turned with the arc seen in the tool face with the hook point set for land clearance. The tool arch is fed into the bore cutting the edge radius to the lands and groove simultaneously forming them together into the same arc. Now all that is left is sanding out the tool marks.

 

[M. De Land]

 

[M. De Land]

This crown has never cut a single patch since the day it was finished.
The crown integrity has been maintained by the use of a down barrel brass loading rod guide. If you don't use one the crown will begin to show the effect of rod wear very quickly and accuracy will deteriorate.

 

[M. De Land]

The first part of any crown to go when loading rod wear is present is the land corners, usually in one quadrant of the muzzle more than others.
A patch will mitigate "hide" the inaccuracy effect better on a ball than will a grease or paper patch bullet but it is still there and will eventually show up.
Also a ball is steered by it's waist and a bullet by it's base which makes it more inherently shape stable and less effected by the "retro-fire" effect of gas escapement on one side of a worn crown than the other.