The Over-Rated Crown

[X-man]

Fascinating write up!

I went over the bars of my dirt bike at about 20MPH with my 340 Weatherby on my shoulder. I landed head and muzzle first with the muzzle digging deep into the hard pack gravel logging road. After a great deal of effort I got the gravel out of the bore and fired a few shots to confirm zero...First 2 shots were wild (off the paper) the next 5 were good and on zero!

When I got home I gave the rifle a thorough cleaning then headed to the range...Much to my surprise the rifle was still a solid 3/4 MOA performer. Because of the unsightly crown I took the rifle to my smith who said there was no way in hell my rifle could shoot. I showed him the targets and he showed me his magnifying glass....the bore was screwed (FUBARed) for a good 1/2" from the crown!

I have a 30-06 where I nicked the muzzle (approx 1/32" deep across the entire crown) and it refused to shoot!

There is something going on here that we clearly do not understand.

 

[westcliffe01]

Perhaps I missed it somewhere, but If I got the jist of it, this was a 308 shooting Federal .308 Gold Medal Match 175 grain Sierra Matchking out of a 24" barrel.

I wonder what the residual pressure is from that ammo when the base of the bullet reaches the muzzle ? It is possible that a cartridge like a 300WM which contains more powder and operates at higher pressure might not have shown the same result.

In addition, all the testing was done with a boat tail bullet. Is it not possible that any form of flat base bullet might have reacted more adversely to this treatment, since the base of the bullet leaving the bore opens up the gas passage in a far more abrupt manner than the tapered end of a boat tail bullet which opens it more gradually ?

If the author had cut the barrel down to shorter lengths, recrowned it and then damaged that crown (and used different style of bullets) one would have obtained a more multi dimensional set of data compared to this single variable style test.

 

[J E Custom]

Good read.

All the test show that the crown may not be that important but instinct tells me otherwise.

I am a big believer in testing a theory and coming up with a solution and the velocity and Standard deviation part of the results I can also believe doesn't change much. But the accuracy part, especially at long distance would be the one I would have trouble with.

I trained under a master Gunsmith and an accomplished Bench Rest Shooter, That many times crowned his new rifle over and over until it shot like he wanted it to.

His philosophy was that the crown was the last thing the bullet saw that he had control over and like everything else It was very important.

I have repaired/accurized many rifles by simply crowning them and don't now what it takes to make a bad crown, Just a good one.

All the things we talk about have different importance to different people based on there experiences
and are subject to debate .

I would like to see the same test performed a 1000+ yards. I think that would change the results, If not I probably would not change my mind anyway just because of the way a bad crown looks.

Others can and do get by with a lot less than some, But others will keep on being anal about everything
and that's OK to If it makes them happy and gives them confidence

As to the type of crown ? There are many different opinions on this also (Surprises) I prefer the single point crown cut on a Lathe. there are good crowning tools for doing one without dissembling the rifle,
but I prefer the lathe cut crown when possible.

I also like the 11o crown. Not because it is any more accurate but because it makes the crown edge
more durable .The 11o crown edge has a 101o angle instead of 90o (Like the difference in a knife blade sharpened at 25o or 18o the 25o will hold up to abuse better.

Thanks for the post. It has been enlightening And again, This is just my opinion.

J E CUSTOM

 

[Kado101]

I was told by a good smith that an 11 degree crown was more accurate. He says he has re-crowned barrels for guys that eventually bring their other rifles to him to be crowned at 11 degrees. I have a 204 that I will take to him this fall. It will shoot 1 ragged hole at 30 yards but at 100 no hole will be within 2" of each other. I have tried different grains of powder, different powders, different bullets and different bullet weights with the same results. I free floated the barrel and I have even tried 3 different scopes. If re-crowning doesn't work it will belong to someone else. By the way it is a Remy 700 SPS Stainless

 

[AZShooter]

Interesting information Alan,

Your imperfect crown test has me scratching my head. All I can think of is that the best crown you used also had some imperfections. Like the idea of testing the variety of crowns at a longer distances. I would imagine it would distinguish the levels of damage.

I remember Rick Jamison doing some BC work decades ago. I was amazed then to read that different velocities from same rifle yielded different average BCs. No surprise that you encountered BC shifts for each shot.


I have encountered many hunting rifles both custom and factory with slight imperfections to badly damaged crowns. After cutting a new crown on my lathe witnessed improved groups with ALL rifles with no other changes.

I will say that without the aide of a borescope it is difficult to tell the difference between an excellent crown and a slightly damaged crown. To be honest I don't know the magnification differences between your stereoscopic microscope and my hawkeye borescope. Almost ALL the rifles I see including customs and new from factory have imperfect crowns.

I asked every gunsmith in my city if they used a borescope. NONE did. I actually proved to one with HIS rifle that his crown was substandard. I was working up loads for his new rifle and told him my borescope inspection showed a flawed crown. He tried several methods and after three attempts he made an excellent crown. After each attempt we would look at the crown and see imperfections. The tool bit had to be resharpened and the third attempt it did a good job. The rifle's group size shrunk dramatically from his original crown finish.

I'll stick with as close to perfect crown every time.

 

[specweldtom]

I have always believed that an even slightly damaged or worn crown was an accuracy killer. Looks like I can start looking somewhere else. The ability of the rifle to shoot a couple of wild flyers from a vandalized muzzle and then recover is astounding.

I can't help requiring as perfect a crown as possible, but now it's on the premise that it can't hurt, rather than that it's absolutely necessary.

I prefer a Winchester type 90 deg singlepointed recessed crown done in the lathe, but if I didn't have to give the muzzle some protection, I would just singlepoint a 90 deg face on the muzzle with no recess, (and I sometimes do that on a rifle with a brake).

An excellent article, with solid methodology. I do believe the results, but still can't stand less than an apparently perfect crown. Too old to change.

Tom

 

[jsnell]

I realize this discussion is a couple of years out of date (its 2 years later now), but I couldn't leave well enough alone. Didn't anyone notice that all the damage done to the crown that failed to destroy accuracy was of a negative nature - that material was removed, whereas all of the positive damage (the punch that left a pin sticking into the bullet path did destroy accuracy until the bullet passage (shot 3 if I remember correctly) had removed the intrusion, at which point accuracy was restored. Here's what I've come away with - anything that changes the bore shape to out-of-round, anything that changes the bore line significantly i.e. bending, and anything that creates an impediment to bullet travel (copper fouling and deformed barrel material) will cause deterioration to accuracy. Things that remove bore material but don't interfere with bullet travel probably don't make a whole lot of difference. When we get to crown shapes, and uniform bullet release I believe the difference between a perfect crown and a negatively damaged crown is marginal. The escaping, overtaking gas has little effect on the bullet once it is out of the barrel because the gas pressure will dissipate toward the open directions and will not created significant force toward the bullet, with the exception of the jet of gas directly impacting the base of the bullet, which might add a small amount of velocity.

 

[EdWalton]

J E Custom

Have you done any studies on how a good crown and muzzle brake work together. I enjoy your videos and would appreciate your comments on the subject.

Thank You

Ed

 

[ChrisP]

I'm late to the discussion but very interesting reading.

My single experience might be somewhat at variance with the published results. I have an accurate .223 HB varmint rifle that had a "mishap". I was riding the quad along a bumpy farm track and the mounting on the front gunrack yoke broke, the end result being the barrel skewered into the farm track which was semi-hard at the time. After carefully cleaning the debris out and checking for obvious damage, a test fire showed the accuracy had gone off dramatically.

Back at my gunsmith buddy's place, he had a look at it and the only thing he could spot was a -very small- ding in the crown, hardly noticeable even with a loupe. We did nothing but recrown it and accuracy was immediately back to what I expected.

 

[mustang58]

There was an article in Precision Shooting a few years ago about this very thing. The guy actually was cutting off the end of the barrel with a hacksaw and shooting groups. The groups didn't change in size much; only the location of the group. It was interesting to say the least.

 

[gunner69]

I never really understood why you would use a bore guide on the chamber end but not on the muzzle crown end. A jag and rod will drag and strike the muzzle crown area hundreds if not thousands of times cleaning during the life of a barrel. I created a simple bore guide for the muzzle crown end and it works really well. We have numerous sizes. There are some good videos on the site too which demonstrate the issue and how the Crown Cradle works. Hope this helps and maybe is seen as a solution or least as extra insurance/precaution for the precision marksman.

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