Muzzle re-crown

[stagpanther]

My first go at doing this, I bought this 350 legend AR barrel a couple years ago for an AR build, I never liked it because it didn't group well--especially compared to my savage bolt gun. I decided to pull it out of the back corner of the safe and take a second look, after I pulled the brake off and put my Hawkeye through the muzzle I discovered a large gouge on the crown which traversed the bore and rifling. The interesting part is that it seems like the exiting gas was eccentrically turbulated so that an area of "backwash" erosion had started forming around it.

I decided to give Brownell's crown cutting tool a go and went with a simple 90 degree cutter, in retrospect I wish I had bought the 11 and 45 degree ones at the same time, I really had no idea what I would need. The cutting at first seemingly went nowhere, that's when I put a flat file to it and got through the first thousandth or so, after that the cutter had no problem at all, I'm guessing that there was some kind of treatment that made the layer of steel immediately under the surface extremely hard. Everything now is clear of defects at the muzzle mouth and very sharp, clean edge. I went ahead and put the muzzle break back on--but was wondering if it still would be better to chamfer the inside and outside of the crown--or do I have nothing to worry about (as long as I have something over it)?

[mulespurs]

I would go and find a round headed screw and use the round head sticking out of a slower drill and apply some valve grinding compound.

Just go enough to clean up all the rifling and then maybe reverse it a little.

I worked at my house.

All the best,
Ray

[stagpanther]

That's an interesting idea, thanks.

[Shadow9mm]

I tried valve grinding compound, was super coarse.... maybe I got the wrong stuff. But automotive metal polish did a nice job for me, from the car detailing/cleaning section for cleaning chrome and such.

[stagpanther]

Might try em both, thanks.

[4V50 Gary]

We made a crowning tool to make the decorative crown but if you want to leave it flat, that's OK. However, you should put the actual crown on as described by others. We had a bore guide to keep it concentric.

[HiBC]

A ball will rest centered on a circle.

If I had to do it without using my lathe,

I might go find a ball shaped mounted stone,about 3/4 in in dia . As fine of a grit as you can find . 1/4 in shank would be common.

I would not concern myself with a motor. The equivalent of a screw driver handle will do.

If you hold the handle in line with the bore,rest the ball on the bore and just twist your wrist a bit you should get a nice corner break all the way around.

If you break the edge.lands and grooves,all the way around, you do not have a sharp corner subject to damage.

If you don't push any side load,the ball will center on the circle.

I have deburred a lot of smaller drilled holes with a ball shaped carbide burr mounted in an Exacto (or equivalent) handle. The ball,of course,should be larger than the hole. It works really well.

[Clemson]

Shoot that barrel before you try to chamfer it. You could easily do more harm than good. Benchrest shooters have been shooting flat crowns for years. The only downside is that it is easier to damage the rifling with a flat crown, but you are installing a brake, so that will protect the crown.

Bill Jacobs

[stagpanther]

Shoot that barrel before you try to chamfer it. You could easily do more harm than good. Benchrest shooters have been shooting flat crowns for years. The only downside is that it is easier to damage the rifling with a flat crown, but you are installing a brake, so that will protect the crown.

I also have a screw-on crown protector if needs be.

[Unclenick]

Here's a description I've put up before of how to lap the crown with a ball and how to determine the diameter of the ball you need to get a specific crown angle at the edges of the bore. I use a large ball bearing for this that I have cut some lapping grooves into with a Dremel abrasive cutoff wheel. M.L. McPherson uses a large glass marble to do ball lapping at the range if he is messing with barrel-length tweaks there. You want a spherical lap rather than the round-head bolts, IMHO, because I found these bolts are actually elliptical in profile rather than round, which means they won't cut an even crown if you don't keep the bolt and drill pretty well aligned with the bore axis. The sphere will correctly center itself and wear evenly if the muzzle is first cut off square, as is the case here.

The ball lapping method makes a super sharp crown if you do it properly with the back-and-forth action and randomizing barrel rotations described in the text. You will want to be pushing all of your patches through from the breech end until firing softens the edges of the new crown a little. I don't like patching from the muzzle if I can avoid it anyway, but on some guns, it is an issue. The first time I put a lapped crown on a Garand, the cleaning patches were cut out by the muzzle as if a bore-sized paper punch had acted on them. I had to go to a pull-through cleaning cable to have any tails on the patch to do the cleaning.

[stagpanther]

Excellent--thanks for that!

[Unclenick]

It's quick, too. Once the muzzle is square, it is about 10 minutes to done.

[stagpanther]

Looks like a fun project for the winter. The barrel is a 350 legend so I'm not too worried about it; it's not exactly the cartridge of choice at PRS matches.

[DT Guy]

I have a turned brass tool from Brownell's for crowning; it has a round section with a shank machined into it for the drill jaws to grip.

Cost a few bucks, but makes this easy peasey, especially if you do it more than once.

Larry

[stagpanther]

I love Brownells tools but they are hit or miss on availability--what I like about unclnick's idea is there is no cutting edge anywhere and centering isn't essential.

[tangolima]

I did a few with Brownells cutters and brass lapping tools. The results have been good in general. The tools could be better.

The biggest problem with the cutters is chattering. I tried different ways and found super light pressure and super low speed gives the least chattering. They could have "randomized" the cutting edges' positions to totally eliminate chattering. But it would be too costly. Brownells sells a fixture to eliminate chattering. It works well for barrels without front sight. The 45 degree cutter is mostly useless. It chatters rather badly. I bought mine trying to preserve the old fashion rounded profile on milsurp crowns. It never works. I always have to fix it with 11 degree cutter.

The lapping tools have spherical profile tips. But after a few uses, the lapping compound cuts grooves into the softer brass, ruining the spherical profile. Glass balls sounds like a good idea as glass is much harder I will find a glass marble to try. Maybe I can return those lapping tools to Brownells? Their stuff has life-time warranty.

I think it is beneficial to lap even the crown is protected. A sharp corner is weak. As projectiles exiting the muzzle, steel around the muzzle will break off randomly in small pieces. Lapping breaks the sharp corner in regular fashion.

-TL

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[Unclenick]

I had that problem with the 90° cutter. I discovered that if I used a removable chuck to adapt it to a flexible shaft drill extension, it stopped the problem.

[RC20]

Stop the Press: !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The only thing the crown does is keep you from dinging the muzzle. It does not make it more accurate.

You have a flash suppressor or Muzzle brake.

Leave it alone! You can only make it worse.

Been some test done that proves it can be hacked pretty good and not change much but why take a chance?

[stagpanther]

Been some test done that proves it can be hacked pretty good and not change much but why take a chance?

I've heard about those tests--Brownells themselves did some I believe.

You can only make it worse.

Everyone is good at something. There was that time I used drain cleaner to clean a bore....

[Shadow9mm]

Originally Posted by stagpanther

I've heard about those tests--Brownells themselves did some I believe.
Everyone is good at something. There was that time I used drain cleaner to clean a bore....

Saw a guy who spilled red bull on a gun once, think it was a kel tek, ate the bluing, things happens. Your right though. Some people are mighty good at machining work. Never know. Already did a good job from the looks of things.

[stagpanther]

Some people are mighty good at machining work. Never know. Already did a good job from the looks of things.

I get things right sometimes--usually after doing them wrong at least once. I'm jealous of those people who do it perfectly right every time. I'm also jealous of those people who get perfect parts every time--I have an amazing ability to attract defects.

[std7mag]

I'm just wanting to know what ever in the world would make you think that an AR would be as accurate as a Savage bolt action??!!

Realistic expectations, Stag!!

I've watched factory Savage rifles out perform full on custom bench rest rifles.
Several times.

[stagpanther]

I'm just wanting to know what ever in the world would make you think that an AR would be as accurate as a Savage bolt action??!!

Realistic expectations, Stag!!

I've watched factory Savage rifles out perform full on custom bench rest rifles.
Several times.

I never did expect it to come close to my savage bolt rifle--but I was hoping to get close to what my AK and AR47 can do, I figure that's reasonable. I find leading in the bore from soft points, so I figure the bullets are getting "mashed around" in process of cycling and firing.

[tangolima]

Originally Posted by RC20

Stop the Press: !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The only thing the crown does is keep you from dinging the muzzle. It does not make it more accurate.

You have a flash suppressor or Muzzle brake.

Leave it alone! You can only make it worse.

Been some test done that proves it can be hacked pretty good and not change much but why take a chance?

The crown is the muzzle, where the bullet leaves the rifling.

-TL

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[tangolima]

Originally Posted by Unclenick

I had that problem with the 90° cutter. I discovered that if I used a removable chuck to adapt it to a flexible shaft drill extension, it stopped the problem.

That's interesting. I'm going to try it next time I recrown, together with the glass marble for polishing. Thanks.

-TL

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