Dual Crown on Barrel

S

Silverfox

Guest
First off, I am not a gunsmith, but want to be able to expalin what I want and how to accomplish it to my gunsmith. I heard about someone having a "dual crown" cut on their rifle barrels. They explained that the muzzle has an 11 degree bevel to the edge of the barrel diameter for optimum gas escape on the base of the bullet and the acutal crown has a 60 degree/20 degree cut. The 60 degree cut is for the cleaning brush to re-enter the bore without damaging the bore, and the 20 degree cut is to break the 60 degree cut right at the actual origin of the rifling.

Is anyone here familiar with that type of crown? If so, do you have an illustration of it and would you please explain to me, how it is supposed to be done? Of the 20 degree and 60 degree cuts, which one is supposed to be done first?

Thanks for any help you can render on this topic.
 
A friend and benchrest shooter showed me how to crown, and it works.

I indicate the muzzle in, just like I would to chamber it, and face it off with a sharp left facing tool. I turn the tool to about 45 degrees, and set the compound rest to 60 degrees and make a clean chamfer 60 degrees backing the compound out very slowly, oiled, with the lathe turning 300 rpm or so for a good finish, just enough so it chamfers the lands and groove about .020. I then run a q-tip in it to make sure it is a clean cut and I did not leave a burr.

On the hunting rifles, I've done the same, with a recessed crown about .075 deep and half the muzzle dia., for idiots that rest the muzzle on stuff,ya know, to protect that critical surface.

There are lots of opinions/other ways on this stuff, so this could be a good subject.

Ben
 

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For the sake of discussion...

There are several ways to crown. In order of "cleanliness," i.e. squareness, lack of burr, etc. they are:

1) Lathe cut either 90 degrees (straight facing cut) or 11 degrees or some other relatively "flat" angle and then lap the surface with a brass lap and compound. Finish with, say, 800 grit. This may leave a slight "burr" which can usually be removed with a Q-tip. Rifling is finished almost perfectly, but the upright square corner is easily damaged.

2) Use Dennis' method of 60 degree piloted reamer. This almost always produces a burr- free muzzle with the additional advantage that the rifling lands are angled inward allowing for better durability. Finish the rest to taste (counterbore, flat, any desired angle, etc.) This is the way I almost always choose to do it.

3) Lathe cut flat or at any chosen angle. This usually does leave at least a slight burr regardless of tool sharpness, angle, etc. (or maybe I'm just not doing it right, I don't know) which can be felt, and can be seen once the first shot is fired. Seems to make no difference which way the tool is fed (in or out.)

I would think, Ben, that as long as you're only taking a lathe cut, you will most likely leave some burr regardless of angles, feeds, etc.....
 
Crowns

The only requirement of a crown, as far as accuracy is concerned, is that it be truly 90 degrees with the bore, and burr free.
Aside from that, most of it is just speculation.
Like Dennis, I do counterbore my crowns, but for no other reason than I like the way it looks.......jackie
 
I want to thank each of you who responded for taking the time to enlighten me on this subject with precise written instructions as well as photos and drawings. I will pass along this information to my gunsmith.
 
Crow99 said:
I would think, Ben, that as long as you're only taking a lathe cut, you will most likely leave some burr regardless of angles, feeds, etc.....
Click to expand...

Crow

The first started with a flat facing crown, as recomended by a F-class shooter/gunsmith that has been helping me. I found it difficult not to produce a tiny burr, and this 90 degree edge was sharp, and was a stress riser in my opinion.

A short range shooter I know, told me that he had a lot less trouble with a 60 degree chamfer, which made sense to me. That means the critical surface had a very obtuse angle (150 degrees) and was less likely to extrude or produce a burr.

A reamer may be better, but I believe, from close inspection, I'm leaving a burr free surface.

Jackie/Dennis, what reamer do ya'll use, I might try that if you think it's a cleaner surface, or do you think a lathe is ok?
 

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I had Keith Francis grind me a 60 degree piloted reamer about 1970 or so... one reamer with about a dozen pilots for various calibers ... I also have some JGS reamers I bought from a private sale. Dave Kiff (Pacific Tool) can also supply you...

The reamer in my view leaves a smoother finish then the lathe.

I think so many gunsmiths leave the crown with a sharp edge is because they think it is the only way to do it. Some shooters may think the same way...
 
Dennis Sorensen said:
I had Keith Francis grind me a 60 degree piloted reamer about 1970 or so... one reamer with about a dozen pilots for various calibers ... I also have some JGS reamers I bought from a private sale. Dave Kiff (Pacific Tool) can also supply you...

The reamer in my view leaves a smoother finish then the lathe.

I think so many gunsmiths leave the crown with a sharp edge is because they think it is the only way to do it. Some shooters may think the same way...
Click to expand...

You talked me into it, I'll be getting a reamer for this step.

I have a few 60 deg reamers, but they have no pilots. I think the pilot is probably key.

I always wondered how they get a nice edge when a barrel is counterbored for a muzzle break? It would also be difficult to inspect it way up in there.

Ben
 
Dennis Sorensen said:
I had Keith Francis grind me a 60 degree piloted reamer about 1970 or so... one reamer with about a dozen pilots for various calibers ... ...
Click to expand...

thanks for your reply Dennis, your experience is appreciated. I read all of your posts, especially on 700's...I'm just starting learning these tricks of the trade, and I was born in 1971, and never ran a lathe until the mid 80's.

Education is expensive...and I owe you guys a lot of money...My first 10 rifles shoot superbly, from the advice given here no doubt!


Ben
 
Finally have a photo to share

The first definition I received with the 20º cut was wrong. The gentleman was trying to tell me there was an 11º target crown from near the outside edge of the barrel and on in to the bore with a 60º bevel cut to meet the lands and grooves. I'll add a photo below here to illustrate.

DSC_0012.jpg
 
That 60 deg chamfer that is talked about; is that included or 60 deg per side?
 
Ben

I do not use a reamer in crowning. I single point the crown, facing from the inside out.
I use a very sharp, positive rake tool that I grind, using a piece of 883 cemented carbide, on my tool grinder. I take the last couple of cuts taking just .001 or .002 at a time, hand feeding very slowly,with the machine running at about 700 rpm. I just touch the corners with some 600 emory paper.......jackie
 
I'm of an opinion

jackie schmidt said:
The only requirement of a crown, as far as accuracy is concerned, is that it be truly 90 degrees with the bore, and burr free.
Aside from that, most of it is just speculation.
Like Dennis, I do counterbore my crowns, but for no other reason than I like the way it looks.......jackie
Click to expand...
,,,,,,,,,,,,,,,,,,,,,


If Jackie is able to win competitions with this practice/theory which I believe is 100% right, those self proclaimed experts claiming, that "their angle" is better than any other angle are in my opinion imbeciles.

Shoot better
Peter
 
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