Barrel crown question

[rmist]

Over the years shooting I have seen the barrel crowns go from the 11 degree to flat and or recessed. Is one more accurate than the other ? What are the pros and cons of each ?

So which one is better ?

Thank you,
Rmist

 

[clowdis]

Lets start this off with a controversial reply. To do an 11 degree crown and keep the bore square you need to indicate the bore perfectly and then cut the 11 degree with a boring bar or sharp turning tool. To do a recessed crown all you need to do is put the barrel in a 3 jaw and cut the crown with a boring bar. The recessed crown will be square to the bore given that the barrel is running straight. SO, in general, I would feel more comfortable that an 11 degree crown would be closer to perfect than a recessed one. Please understand that the same care can be taken with a recessed crown and result in a perfect job also, but I think that it is sometimes used as a quick and dirty way to finish a barrel.

 

[jonbearman]

What do you do if you end up with a slight burr with a recessed crown?Do you just shoot it or lap it?

 

[Rustystud]

I guess I have to do everything different.

First, I never part off barrels in the lathe. I cut them with a band saw. I then dial them in the lathe and use a center drill to open up the new muzzle end. Then I use piloted tooling 79* or 90* to turn the new crown. I finish the crown with 1000 grit emery cloth for a mirror finish with no burs.

The reason do this is single point tooling induces stress into the barrel and tends to distort the bore. Usually causing a tight place in the muzzle.

Dave Kiff at PT&G, Dave Manson and Manson Precision Reamers, and JGS all make these piloted tools.

Nat Lambeth

 

[clowdis]

A good crown is a quick job that takes an extrodinarily long time to set up for, therefore it lends itself to hand tools that speed the job up. If the bore is set up and running square and concentric you can just touch it with a countersink tool to add a chamfer to the tip of the lands and then finish with emery. I prefer to finish competition rifles with an 11 degree crown and hunting rifles with the recessed crown to keep it out of harm's way. I always indicate the bore and finish with a small chamfer on the lands regardless of which type crown I use. I have also tried leaving the lands square (sharp) but couldn't see any accuracy advantage with either.

 

[kjcpoint]

I dont part barrels either. Indicate the bore and take very light cuts with a sharp boring bar. Then cut a small 45 degree chamfer on the lands. 11 degree recess or what we call a Boyer crown, flat to 11 degree and back to flat. Whatever looks good.

Kyle

 

[Tozguy]

I guess I have to do everything different.

First, I never part off barrels in the lathe. I cut them with a band saw. I then dial them in the lathe and use a center drill to open up the new muzzle end. Then I use piloted tooling 79* or 90* to turn the new crown. I finish the crown with 1000 grit emery cloth for a mirror finish with no burs.

The reason do this is single point tooling induces stress into the barrel and tends to distort the bore. Usually causing a tight place in the muzzle.

Dave Kiff at PT&G, Dave Manson and Manson Precision Reamers, and JGS all make these piloted tools.

Nat Lambeth

Nat, does it matter whether the pilot is solid or live?

 

[watercam]

FWIW there was a article in Precision Shooting (RIP) about this very comparison (regardless of the technique to accomplish the job). Johnson or Johnston I believe was the author - hunband/wife team of Long Range rifle builders. In it they essentially said they could not see any difference between the two. I needed to re-cut a crown on one of my Palma rifles - cut both on the same barrel. Same group sizes at 600 yds. w/ match boat-tail bullets.

 

[civil82]

There was also a PS article several years ago where the author intentionally damaged the crown to varying degrees and group tested. If I remeber right, he used a chisel and ball peen. Some of the results were quite surprising.

 

[LHSmith]

FWIW there was a article in Precision Shooting (RIP) about this very comparison (regardless of the technique to accomplish the job). Johnson or Johnston I believe was the author - hunband/wife team of Long Range rifle builders. In it they essentially said they could not see any difference between the two. I needed to re-cut a crown on one of my Palma rifles - cut both on the same barrel. Same group sizes at 600 yds. w/ match boat-tail bullets.

Yup. I read that. I was in the February 12 issue. I did not give the article any merit due to flawed test methods.....first of which they made no attempt to read conditions-NO FLAGS in their evaluation testing. Of note, she did the crowns on the lathe using a parting tool.

 

[LHSmith]

There was also a PS article several years ago where the author intentionally damaged the crown to varying degrees and group tested. If I remeber right, he used a chisel and ball peen. Some of the results were quite surprising.

March 2011 issue. .308 HB model 70...w/ fresh 11' crown 5-shot group =1.02"....w/ notch in crown @12 o'clock w/ dremel tool 5-shot group = 1.15 (mostly vertical)....dinged crown at a land with a pin punch enough to cause serious burr with metal protruding into bore, 5-shot group =.68"....half-moon cut around 1/8 of crown circumference gouging it with carbide tool, 5-shot group = .75". Finally after dinging more of the crown AND gouging the inside of the bore 1/2" deep they netted a 1.75 in group for first 5 shots....BUT the next 5-shots were .700. Go figure. ???
In the July 2000 issue they tested muzzles that were not perpendicular to the bore. One @ a 12' angle facing up and to the right, crowns finished by using JB and a brass round head screw spun in a drill. The groups from the cocked crown followed the direction of the muzzle. The factory crowned .222 TCR'83 yielded a 5-shot group of .87 moa, the cocked crown yielded a two groups that averaged .70 moa, 3-1/4" above and right of POA. Finally, the author cut the muzzle square, lapped in the crown using the JB_brass screw, and netted .72 MOA groups.
I really miss the PS rag, the issues prior to 2009.

 

[newgun]

I remember reading a test were they cut and or distorted the end of bullets and was all so surprised at the results. At short range

I really really miss p.s. mag. all so.

 

[LHSmith]

I remember reading a test were they cut and or distorted the end of bullets and was all so surprised at the results. At short range

I really really miss p.s. mag. all so.

Yes.To clarify, the distortion in the tip region caused minor changes in POI....but the slightest nick in the edge of the flat base caused big changes.