Repair of crown damage

24 May 2001, 03:14

<JohnA>

Attached is a pic of a damaged crown. I'd appreciate any opinions on effect on accuracy and can I fix this myself, or do I need to get it to a smith?

Thanks!

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24 May 2001, 03:45

Zero Drift

JohnA - Damage to the crown of your muzzle CAN effect accuracy. Like you, I get really nervous if I find any damage around the muzzle. It is fairly easy to damage the crown. Cleaning rods and jags can damage the crown if you are not careful. However, if you are not seeing any accuracy problems, then the damage is only cosmetic. I have had several guns re-crowned. I would not wish to tackle this project at home. If things are not absolutely square, accuracy will suffer. It is a simple, quick, and cheap operation for a gunsmith.

Good picture by the way...

[This message has been edited by Zero Drift (edited 05-23-2001).]

24 May 2001, 03:55

Paul H

Go and shoot it, and find out. I think that many folks are coming to the realization that the crown, in the big scheme of things, isn't that important to accuracy. I'm not saying there is no effect on accuracy of a damaged crown, but that we give more credit to the crown then is due.

It really comes down to your accuracy criteria. If you are after the utmost mechanical accuracy that the rifle is capable of, then find a competent gunsmith who will remove the barrel from the action, dial it in to .0001" of concentric on the lathe, and cut a nice crown. Of course if you go with a 90 degree counterbored crown, the concentricity isn't as critical as on a 79 degree crown.

As far as doing it yourself, you can get a crown cutter from Brownells, or use a slotted brass screw and abrasive compound powered by a hand drill. Your results won't be as good as a perfectly set up barrel in a lathe, but you'll save a few bucks.

Personally, I'd just shoot it and see if accurcy has been adversely affected. If it still shoots, don't worry about it. If it doesn't shoot, and you don't have the tools,

I'd put the money for the tools into having a smith make the crown better then it came from the factory, but, make sure your smith is capable of that, not all of them will go to the effort to really dial it in. Ask the smith if he uses a 4 jaw chuck, a cats head to support the end of the barrel, and to what tollerances he uses when dialing in the concentricity of the bore. If he says he dials in the od of the barrel, or uses a 3 jaw, then make a permanent note not to use him on critical machining opperations.

24 May 2001, 04:06

<JohnA>

I should have mentioned that accuracy IS an issue with this rifle. Without getting into a great amount of detail, the barrel has less than 500 rounds through it (.280 Ackley). It is a custom rifle that had a barrel coating on the Hart barrel, and the previous owner removed the barrel and turned the coating off on his lathe.

I have been load testing, but haven't been pleased with the accuracy or consistency. I've been problem solving one thing at a time, and yesterday I really examined the crown and found this damage. Supposedly proven loads (less than .5" @ 100 yards) won't group consistently for me. Fireforming cases with flat base bullets have given me some excellent groups, but 3 different types & weights of boat tails have given me inconsistent groups.

The action has been trued etc, the action and first two inches of the barrel have been bedded, and the scope is a proven Weaver in loopy mounts.

When I saw the crown damage, I thought this might be my problem.

24 May 2001, 05:07

Robgunbuilder

I would not tolerate such a crown. I believe that a MAJOR effect on accuracy is the quality of the crown. Everyone who shoots benchrest quality rifles knows this. You can fix this yourself if you are carefull using some crowning tools from Brownells or take it to a competent gunsmith. This is a simple recessed flat crown. Have the gunsmith just break the sharp edges left from the lathe tool such that a Q -tip run over the crown does not catch any hairs.-Rob

24 May 2001, 05:18

Zero Drift

JohnA - Not suggesting that you go blow your money, however, a few bucks invested with a good gunsmith can save you a lot of headaches in the long run. If your gun is not grouping, then have the smith cut a new crown. While the action is out of the wood, inspect the stock for barrel contact and check the bedding. You may want to go ahead and re-bed the action and check everything else.

It may take a week or two and a few bucks, however, in the end, you will be able to eliminate several accuracy variables. From there, you can concentrate on load development.

24 May 2001, 06:07

Paul H

Based on the further info, I'd say, by all means, take it to a competent smith to have it re-crowned. I was going to mention boat tails being more sensitive then flat base bullets, but you beat me to the punch.

As was mentioned, for top notch accuracy you need a proper crown. It just comes down to what one considers acceptable. I'm personally not that picky about hunting rifle accuracy, but everyone has different standards.

24 May 2001, 07:15

Bob338

Don't be disappointed if you have the barrel recrowned and it still doesn't shoot well. Re:"Fireforming cases with flat base bullets have given me some excellent groups," it would seem if the crown is bad you would get the inconsistency with all bullets. Many a match grade barrel will not shoot boattails consistently and it has nothing to do with barrel accuracy or crowning. I've never understood why some barrels will and other won't. Recrowning certainly won't hurt. Just don't expect miracles with boattails after you do. Bob

24 May 2001, 14:35

<JohnA>

Thanks guys for the comments and inputs. I've decided to go ahead and have the rifle re-crowned, just to be sure.

Really appreciate the help!

John

25 May 2001, 07:32

<Mats>

quote:
Originally posted by Bob338:
...it would seem if the crown is bad you would get the inconsistency with all bullets.

Bob, BT's are more sensitive to bad crowns, they depend more than FB's on the gasses funneling out evenly.

A lack of balance in the gas flow will increase bullet wobble by pushing its base towards the side of the least flow. BT's get more of the bad treatment since the tapered base offers more "leverage" for the fast moving gasses.

-- Mats

[This message has been edited by Mats (edited 05-24-2001).]

25 May 2001, 16:31

<k wood>

That really is a good picture, post us a picture after you get it recrowned.

29 May 2001, 00:24

<JohnA>

Got the rifle back with the new crown cut. I was in a hurry to take the picture, so it may not be as clear as the first. Quite a difference. The rifling is very crisp now at the muzzle.

I intend to resume load testing mid week.

Thanks to all who responded on line and via email.

Regards
John

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29 May 2001, 00:41

Phantom Duck

You should see a change in accuracy for the better. Damage as shown in the first picture is the main reason why the benchrest crowd inserts the one piece cleaning rod from the action side. Hope that your problem is solved.

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"If you can keep your head about you when all others are loosing theirs and blaiming it on you..."

29 May 2001, 02:03

<JohnA>

To be honest, this rifle has never seen a cleaning rod from the muzzle end. It's only been cleaned with a bore guide and a dewey coated rod.

I suspect that the marks were made during the lathe process where the coating on the barrel was taken off.

I'll let you guys know how she groups later!

John