Muzzle crowning

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Muzzle crowning

Post by Flytrap1 on 5/5/2015, 8:42 am

Does crowning the muzzle improve accuracy, and does anyone recommend having it done or had it done?

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Re: Muzzle crowning

Post by dronning on 5/5/2015, 8:52 am

All barrels have a crown, the only reason to recrown it is if it has been damaged.

- Dave
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Re: Muzzle crowning

Post by Jon Eulette on 5/5/2015, 9:37 am

Not all crowns are equal! I've seen factory crowns that appear ok to the eye, but when indicated/measured were off. If a pistol isn't shooting well and properly built it could be the crown. I used to recrown Rem 700 rifles and nearly always improved the groups with no other modifications to the rifle. Firearms are production items, QC isn't always the best.
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Re: Muzzle crowning

Post by jglenn21 on 5/5/2015, 9:44 am

+1 on the Rem 700 barrels...   everyone of mine has had the crown re-done..

some are good from the factory but lot's are not
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Re: Muzzle crowning

Post by Froneck on 5/5/2015, 10:40 am

I'm thinking the factory will use a cutter that will push a fine burr into the rifling. I see a major improvement when I lap the crown.
 My AW came with a test target but was not getting test groups at 50' I re-crowned but didn't do a good enough job because it still shot lousy groups. I accidentally noticed a burr on the crown, re-crowned again and vertical stringing 2" at 50 yards dropped to 5/8". I'll test it at 25yards and 50' during my next trip to the club.

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Re: Muzzle crowning

Post by Jerry Keefer on 5/5/2015, 12:09 pm

The  muzzle is the transitional region from internal to external ballistics. When the hot, high pressure gases exit, they expand, become supersonic, pass the projectile, and become a shock wave that travels as far as 20 feet.. That is a very basic analogy to a very complex  event. The better the crown, the better the projectile can survive the disruption the event subjects it too. I am a firm believer in aligning both axis when cutting a crown.. Crowns should be single pointed, in a spider. There have been numerous studies on the crown shape..  The shape has some effect on the dispersal angle of the gas flow.. But there is no debate on the concentricity of both the X and Z axis.
Here alignment of both axis is being adjusted as close to zero as possible.. for a chamber reaming... but it's the same exact process for a crown. Adding to what Jon said..I have indicated countless factory crowns for distinguished guns.. I have yet to find one that was concentric..They are done with a reamer.. Not good.
 
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Re: Muzzle crowning

Post by Froneck on 5/5/2015, 1:17 pm

I make my crowning hone with a long pilot that just fits the bore. Roughed on the lathe then ground in my tool and cutter grinder so the crown and pilot are concentric. I undercut the pilot about a 1/2" away from the crown so compound don't lap my bore. Then lap with barrel pointed down so compound don't get to the pilot.

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Re: Muzzle crowning

Post by Jerry Keefer on 5/5/2015, 2:55 pm

Because the projectile usually gets more support from the grooves than the lands in most cases, it's better to indicate off the grooves and single point from the inside out.... Sharp mini carbide boring bar, no lapping necessary. If a pilot doesn't rotate, I don't want it in the bore..
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Re: Muzzle crowning

Post by Froneck on 5/7/2015, 7:53 am

However no matter how sharp a cutter either new or resharpened Carbide, Cobalt, High Speed Steel or Carbon Steel will cut so well that it will not leave a remaining burr because of the force required to cut steel even aluminum (though I know of no aluminum barrel) in either direction though the "out side will be larger than the in. If making a barrel from a blank I do cut the crown as mentioned or if the crown has been damaged I will re-cut it as described indicating in two places to assure concentricity  and alignment with the bore but I always Finish with a lap! Furthermore I see that as the conical section of the lap is cutting the crown it too is being cut and a very small fine radius is formed on the ends of the cut and serves to put a very small radius at the ends of the crown Though being very small and microscopic the transition becomes very smooth especially when using 600 grit and finer that is impossible to accomplish with any type of edged cutting tool no matter how light a cut is taken. As far as the pilot doing anything to the bore being turned by hand is not an issue. A clean, smooth and polished pilot will do far less to the bore than hundreds of bullets being pushed at great speed through the bore being Lead" or Copper containing various unknown contaminants not to mention a cleaning rod especially an aluminum one. Thought I haven't tried it yet I did purchase a jig grinder and will try that one day. I would say it would be a far better way to finish a crown that was cut in the lathe with a micro carbide boring bar by using the Tool Post Grinder.

Frank


Last edited by Froneck on 5/7/2015, 10:15 am; edited 1 time in total

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Re: Muzzle crowning

Post by Wobbley on 5/7/2015, 8:30 am

When I did rifle barreling I used these.http://shop.pacifictoolandgauge.com/index.php?main_page=product_info&cPath=312_10_45&products_id=559.  If I used a quality barrel they shot in the twos (.200 to .299).  I see no reason to treat pistols any different.

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Re: Muzzle crowning

Post by Froneck on 5/7/2015, 9:04 am

Using that type of tool will work similar to a lap but it too will depend on the pressure being applied and how sharp the cutter is, being that the cut is perpendicular to the bore it will not tend to push and will cut similar to a lap. Being similar to a piloted countersink they too will lave a small burr especially when getting dull. Most rifles are shooting jacketed bullets I'm sure copper will eventually remove the slight burr and the escaping gasses of much higher pressure in a rifle barrel will also erode way any slight fine burrs.
 The nice thing about a lap is that it's never dull, can be easily made and works the best.
 I'm sure most companies are using the type tool you list and get good results. Eventually the tool gets dull and will cause burrs and probably why some shoot great out of the box and some don't. I do have a cutter grinder and can sharpen any cutting tool and one especially made to grind taps and countersinks. Yet I prefer to lap the crown. If I'm going to do it I do it perfectly that way I know it's right.

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Re: Muzzle crowning

Post by Jerry Keefer on 5/8/2015, 3:51 pm

Froneck wrote:I haven't tried it yet I did purchase a jig grinder and will try that one day. I would say it would be a far better way to finish a crown that was cut in the lathe with a micro carbide boring bar by using the Tool Post Grinder.
Frank
Hmmmmmmmm, You mean like this..??

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Re: Muzzle crowning

Post by DavidR on 5/8/2015, 4:12 pm

you guys have way cool toys... Very Happy
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Re: Muzzle crowning

Post by james r chapman on 5/8/2015, 4:56 pm

DavidR wrote:you guys have way cool toys... Very Happy

+1

take some time to look thru Jerry's photobucket pics... the drool marks are mine...
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Re: Muzzle crowning

Post by Jack H on 5/8/2015, 5:04 pm

I had a 7.25 fluted HS barrel that was not grouping like it should from the Ransom.  I had a local gunsmith "dress the crown".  I do not know what method he used but it did greatly improve the groups to near my standard expectations which are .75-1.0 with Eley and 1.25-2.0 with middle cost ammo.
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Re: Muzzle crowning

Post by Froneck on 5/8/2015, 9:34 pm

Yes Jerry that's the ticket! Make perfect crowns especially if you have a variator for a taper attachment or power feed on the compound.
 I can't wait to try the Deckel Jig grinder I purchased. Been so busy I haven't hooked it up yet. Shown in the photo at the place I got it with the boring head attached, Came with the grinding head too.


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