Barrel Crown Lapping

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mrh1958

New member
I have a barrel that has been cut off square at the muzzle with no chamfer at all,just a flat crown if I want to lap this barrel is it ok to just use a brass lapping tool and a hand drill? or should I use some sort of chamfer tool to break the edge a bit before lapping? Any chance of getting off center with the bore using the brass lap without using a chamfer tool first?? Thanks
 
How does it shoot now? If it is not shooting up to reasonable expectations I'd get it recrowned. If it is shooting suitably I'd leave it alone.

Sounds like you do not have confidence in your planned process. In that case I'd let a gunsmith do it.

Now, probably 98% of target crowns (benchrest, mainly) are sharp. Putting a bevel or radius on the edge only helps limit damage caused by bad cleaning processes, or in the situations like benchrest, where excessive cleaning takes place. This edge rounding has never been proven to improve accuracy.
 
mrh1958 said:
I have a barrel that has been cut off square at the muzzle with no chamfer at all,just a flat crown if I want to lap this barrel is it ok to just use a brass lapping tool and a hand drill? or should I use some sort of chamfer tool to break the edge a bit before lapping? Any chance of getting off center with the bore using the brass lap without using a chamfer tool first?? Thanks
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I know I will probably cause a plethora of replies here but.....

I crowned a barrel for a guy a few years ago. When he picked it up he started looking at the crown and asked if I was going to leave it sharp like that ? He stated that he had this brass crown lapping tool that goes in a drill and makes it real pretty. Long story short, he takes it home and immediately used the tool and ruined the crown. Grouped like crap. Brought it back, I re-crowned it, he left it alone this time and it shot great. I have NEVER used one of those things ( nor would I ), but I guess it is possible to do it right using one...maybe.
 
I recrowned a .308 Palma rifle that was losing it's accuracy after a couple thou rounds, like 3/8" deeper, and chamfered it with a battery drill, a round head rivet, and valve grinding compound. Shot good enough to get me to Master. That was the end of prize money for me, unfortunately.....
 
Crowning

When you re-crown a barrel in a lathe and you line everything up, bore perpendicular to the face of crown. (I used a dedicated boring bar to cut the final pass of the crown and hone it sharp before each new crown. Why would you want to polish or De-bur the new crown and risk making one side shorter. You want a crown to release the bullet evenly 360 degrees. Any burs left from crowning will be remove by the bullets or the first couple of cleanings. All crowns I did over the years I only received compliments on how well the rifle shoots.
 
I did a barrel a little different my last go around. I crowned this particular straight across as I normally would and all looked good. I took the barrel out and while inspecting one final time I noticed a little shiny spot just inside the crown about .060 in. I think my scotch brite pad that I use to polish the face of the barrel with must have slipped inside a bit. Anyway I didn't like it. I had to make a couple decisions on how I was going to fix my little goof. I really didn't want to cut out the shiny spot as I threaded the muzzle end for a buckys tuner and everything else was dead perfect.
I decided I would try a recessed 11 degree crown. I hadn't ever done this, but I figured now was the time. long story short. I cut the very best, most sharp crown I had ever cut. This crown looks absolutely perfect.
I use a warner HSS insert 1/4" boring bar for my crowns. I have found this tool to be very effective for crown work. In the past it would always take me a couple passes to get a crown I liked using the cross slide. The 11 degree crown using the compound for my feed for whatever reason just worked better. Not sure why, but I am now going to this method from here on out. Lee
 
Skeetlee how did the rifle shoot? Out my way the trend is a flat crown as they all moved away from the 11 degree stating they saw better performance.
 
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Aderondacker said:
When you re-crown a barrel in a lathe and you line everything up, bore perpendicular to the face of crown. (I used a dedicated boring bar to cut the final pass of the crown and hone it sharp before each new crown. Why would you want to polish or De-bur the new crown and risk making one side shorter. You want a crown to release the bullet evenly 360 degrees. Any burs left from crowning will be remove by the bullets or the first couple of cleanings. All crowns I did over the years I only received compliments on how well the rifle shoots.
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Absolutely!...This is the way I think it should be done.

If lapping the barrel, I would re-cut the crown as a final step but would NEVER lap the crown...Yo want it sharp and without burs.
Check it after firing a few rounds using the "Q Tip" test: Clean the barrel and introduce a Q-Tip a couple of inches and slowly pull it out, it the crown catches cotton strands then you have burs.

azuaro
 
AZUARO said:
Absolutely!...This is the way I think it should be done.

If lapping the barrel, I would re-cut the crown as a final step but would NEVER lap the crown...Yo want it sharp and without burs.
Check it after firing a few rounds using the "Q Tip" test: Clean the barrel and introduce a Q-Tip a couple of inches and slowly pull it out, it the crown catches cotton strands then you have burs.

azuaro
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I can about assure you one thing, if you have burrs in the bore after firing a few rounds you do REALLY have problems.
 
JerrySharrett said:
I can about assure you one thing, if you have burrs in the bore after firing a few rounds you do REALLY have problems.
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Yes you do and more so in centerfire...Lead bullets in a rimfire crown with minute burrs are another beast.
 
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Louis
How could one degree of crown shoot any different than another with all else being equal? Dan Dowling, from what I have been told, hates 90 degree crowns. All I really know is that the 11 degree crown I cut looks absolutely perfect under a 10x loop. perfectly sharp, and the lands are nice and square. Best I have ever done for sure. We haven't shot this barrel yet, so we wont know how it shoots for a bit, but I will just about bet a dollar it shoots fine.
I truly think this will be the way I crown from here on out. Lee
 
Flat or 11 degree, I indicate in and cut the crown, then swing the compound around to 60 degrees, reach in and pull a slight chamfer out. It is deep enough to just get to the groove area a little bit.

You brush a barrel to clean then drag a brush back through that sharp crown.

Obermyer does this and I believe Billy Stevens does as well.
 
I always remove my brass brushes before retrieving the rod. but I do hear what your saying Wayne. Thanks a bunch. Lee
 
Skeetlee it would have to do with the way the gases exit the muzzle so the bullet has a clean undisturbed release. With the 11 degee crown the gas can pass the base of the bullet before it reaches the ultimate end of the crown and disturb it's exit.

JLouis
 
Don't have a clue Lee, that's whole nother subject and I 'am not sure how it relates to the original subject at hand. It would be an interesting question to those who do use a tuner in regards to what kind of crown do they use?

JLouis
 
skeetlee said:
Louis
What happens when the muzzle end is incases by a barrel tuner? Thanks man, Lee
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Louis.J said:
Don't have a clue Lee, that's whole nother subject and I 'am not sure how it relates to the original subject at hand. It would be an interesting question to those who do use a tuner in regards to what kind of crown do they use?

JLouis
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Hello Skeetlee and Louis...

I think that this thread will help with your question: http://benchrest.com/showthread.php?88477-Flat-Crown-vs-11-Degree-Which-is-Best-for-22-RF

Regards,

azuaro
 
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