Co-Axial Muzzle Alignment

C

Curious

New member
Ive seen a lot of guys dialing in a muzzle on the lands but only in one place and then calling it good.

That seems to me all they are establishing is radial alignment at one point and not ensuring that the crown is truly cut square to the bore?

I appreciate the bore wanders a little but surely it would make more sense to clock the muzzle t two points over at least a bullets length so that it is co-axially true? Even use a tapered range rod and measure at two points if you didn't have a long enough needle on your indicator?

I would welcome your thoughts guys :)
 
Curious said:
Ive seen a lot of guys dialing in a muzzle on the lands but only in one place and then calling it good.

That seems to me all they are establishing is radial alignment at one point and not ensuring that the crown is truly cut square to the bore?

I appreciate the bore wanders a little but surely it would make more sense to clock the muzzle t two points over at least a bullets length so that it is co-axially true? Even use a tapered range rod and measure at two points if you didn't have a long enough needle on your indicator?

I would welcome your thoughts guys :)
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Curious, The way I look at it. Indicate the muzzle and cut the crown. It will be coaxial at that point. You do your range rod thing and with the bore being not straight and indicate two places, what happens? Your crown will not the square to the muzzle at that point. Does it matter? Probably not. If you have a sharp crown either way you will be good.
 
Curious said:
Ive seen a lot of guys dialing in a muzzle on the lands but only in one place and then calling it good.

That seems to me all they are establishing is radial alignment at one point and not ensuring that the crown is truly cut square to the bore?

I appreciate the bore wanders a little but surely it would make more sense to clock the muzzle t two points over at least a bullets length so that it is co-axially true? Even use a tapered range rod and measure at two points if you didn't have a long enough needle on your indicator?

I would welcome your thoughts guys :)
Click to expand...

I guess I've never seen anybody crown a rifle without running an indicator into the bore and bringing the last inch or more into line with the CL of the lathe.....longer if you've got it of course but really, dialing an inch with a .0005 indicator is more than sufficient IMO.

And I don't know of anyone any more who'd use a tapered/bushed range rod....I don't know of anyone who thinks that could possibly align anything. I sure don't!
 
Curious said:
Ive seen a lot of guys dialing in a muzzle on the lands but only in one place and then calling it good.

That seems to me all they are establishing is radial alignment at one point and not ensuring that the crown is truly cut square to the bore?

I appreciate the bore wanders a little but surely it would make more sense to clock the muzzle t two points over at least a bullets length so that it is co-axially true? Even use a tapered range rod and measure at two points if you didn't have a long enough needle on your indicator?

I would welcome your thoughts guys :)
Click to expand...

Most Benchrest Bullets only have about 3/16 to 1/4 inch of bearing surface, put your indicator in about 1/8 inch and split the difference. That's what I do.

Or you can adjust the barrel with a spider on one end and the chuck on the other, and adjust the barrel until that final 1/4 inch, (or what ever straight shank your bullet has), runs dead true, and face it square.

Go for it.
 
Thanks guys, I know it is quite easy to overthink this but on the other hand the subject is worthy of some thought.

I prefer direct dialing onto the lands but threw the range rod in to see how others felt. Ive found range rods didn't repeat very well but then maybe I was doing something wrong? Yesterday I had a barrel to thread and crown and I had been thinking about this leading up to it. My thoughts were that if you took a reading from only one point in the muzzle but say your chamber end was running out a long way then it would be possible to cut a crown that was quite far off.

Yesterday I clocked the muzzle about 1/4" deep and also clocked the inside of the chamber mouth, I had 0.0005" run out on the chamber mouth and the muzzle was running true at the single point. As I came in or out 3/16 the indicator would vary by 0.0002" or less. That seemed more than good enough so I cut things at that.

I mentioned this some time ago in another thread but I know someone who crowns in his 3 jaw and sets the chamber end up to within a couple of thou clocked on the outside. His rifles shoot very well but it leaves me feeling uncomfortable that Im not doing as much as I can to get things true, maybe thats now got me going the opposite way and Im getting way too anal about it.
 
One other fact about crowning. If you are cutting a sharp crown the exact bore alignment is not that critical. If you are beveling the crown/bore intersection, by any amount, and shooting boat tail bullets, exact bore alignment CAN be important, depending on the bullet used, the barrel quality, and your expectations of outcome.

.
 
Having access to electron microscope images of crowns fresh and otherwise I'll opine that the single most important thing TO ME is that the crown to be cut be absolutely centered such that the grooves are as close to zero'd as possible......I would never cut a crown with a three-jaw after watching the way metal smears off a trailing edge.
 
NezRongero said:
What is the drawback using Deltronic pin to dial the bore before crowning?
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Having a snug fitting Deltronic pin in the muzzle is a good way to align the muzzle for crowning especially if you are doing a sharp crown.

For a beveled edge crown I would still use a good 0.0001" dial indicator to do a final check. A snug fitting pin will also give a hint if there is significant bore curve at the front..
 
Just for the sake of conversation. Can anyone show me the accuracy difference or other possible affects "on a target" or other reliable data between a tapered crown that is perfectly centered and one that's let say is off center by .003"?
 
Dave Tooley said:
Just for the sake of conversation. Can anyone show me the accuracy difference or other possible affects "on a target" or other reliable data between a tapered crown that is perfectly centered and one that's let say is off center by .003"?
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There was an article years ago in Precision Shooting where a test was done by crowning with the barrel cut off crooked, not centered, that kind of thing. Not much difference in how any of the crowns shot if I remember correctly. About the only difference was point of impact on the target. It's been a long time ago when I read the article and no longer have any of the old issues. Don't know whether it was included in the Benchrest Primer or not. It involved recrowning the same barrel and reinstalling it. Not too sure how valid the point of aim shift was that was attributed to the crown as I imagine that there would be some point of impact shift by just removing and reinstalling the barrel time after time.
 
MilGunsmith said:
How about using a piloted cutter for a beveled crown? I know a lot of sniper rifles are done this way.
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I've done close to 5000 Bartlein barrels plus a few hundred others since 2009. All are indicated in with a pin gage to within a few tenths, all have a chamfer on the bore. Never had any complaints. A piloted reamer would likely induce more variations than the way I do it as tolerances stack up. With Doppler data becoming available to us peons there are far more variables in regards to bullet behavior than anyone realized. Surprisingly the importance of a perfect crown is not a priority.
 
How Important Is The Crown..................????

Dave Tooley said:
I've done close to 5000 Bartlein barrels plus a few hundred others since 2009. All are indicated in with a pin gage to within a few tenths, all have a chamfer on the bore. Never had any complaints. A piloted reamer would likely induce more variations than the way I do it as tolerances stack up. With Doppler data becoming available to us peons there are far more variables in regards to bullet behavior than anyone realized. Surprisingly the importance of a perfect crown is not a priority.
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As Mike and Dave have stated.....
many tests have been done to determine the importance of the crown ........ regarding concentricity,finish and perpendicularity...all tests prove it is of secondary priority.......
google the subject..... interesting reading....... Harry Pope once wrote of a real life situation regarding crowns....
my believe is it is more important in a rimfire (lead bullets )...than centerfire shooting jacketed bullets.....
bill larson
 
Dave Tooley said:
I've done close to 5000 Bartlein barrels plus a few hundred others since 2009. All are indicated in with a pin gage to within a few tenths, all have a chamfer on the bore. Never had any complaints. A piloted reamer would likely induce more variations than the way I do it as tolerances stack up. With Doppler data becoming available to us peons there are far more variables in regards to bullet behavior than anyone realized. Surprisingly the importance of a perfect crown is not a priority.
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I do it the same way. Indicate on a pin gage and cut a 60 degree chamfer at the bore. The rest of the shape of the crown, 11 degrees, flat or whatever isn't of any importance. Even put a 30 degree crown on hunting rifles with a 60 degree chamfer single point cut at the bore. The 60 degree bevel at the crown isn't the current flat sharp edged crown that so many people want to use, but seems to work without having to recut a new crown every few hundred rounds when the flat crown rounds over or worse nicks.
 
OKAY......after thinking about it for a minnit I realize that probably the main reason I run a dial probe into the bore is because I believe that prior to me facing of a perfect crown it's highly unlikely that anything on the front end is clean and burr-free.....range rods, deltronic pins, anything that sets in/on the muzzle surface is setting on a sod-off or at best a hand-deburred surface. The only way to indicate an undisturbed surface is to hack off the lapping bell and reach in with an indicator the way I see it....plus, until I indicate the grooves in, any offset cutting I do has to leave trailing edge burrs where it runs in and out of cut....I think the cut should to start so well centered that it never drops off an edge...

I just can't see the advantage of stuffing a hardened steel pin into the bore and I certainly can't get behind tapered "range rods." Conversely, I can't see a disadvantage to letting an indicator ball walk over the lands.

According to the inspection I've done. a burred edge will shoot off differently than a clean, pulled-back edge. I realize the lands all show some pull-off but they're all similar and all on the side.

But then I'm one of those guys who think the crown is important.

My Opinion

al
 
Nez,

Tolerances stack up between the reamer, bushing and barrel. It can be done but not by just shoving a center reamer in. I was talking to a wise man by the name of George Kelbly one day. Coming from the era of small lathes and working between centers he a bag of tricks somewhat different from my own. We all know that the ID is not concentric with ID on barrels so the question is how do you hold/spin either the barrel or the reamer in a way that mitigates the concentricity issue. It's so simple I felt pretty stupid when George told me his trick. Set up the barrel with the muzzle running in a steady rest. With the center reamer in hand run it to the depth you want, then pull it sideways towards you wait for it to stop cutting. You removed all the play out of the system and it finishes cutting on one flute. So simple.
 
alinwa said:
OKAY......after thinking about it for a minnit I realize that probably the main reason I run a dial probe into the bore is because I believe that prior to me facing of a perfect crown it's highly unlikely that anything on the front end is clean and burr-free.....range rods, deltronic pins, anything that sets in/on the muzzle surface is setting on a sod-off or at best a hand-deburred surface. The only way to indicate an undisturbed surface is to hack off the lapping bell and reach in with an indicator the way I see it....plus, until I indicate the grooves in, any offset cutting I do has to leave trailing edge burrs where it runs in and out of cut....I think the cut should to start so well centered that it never drops off an edge...

I just can't see the advantage of stuffing a hardened steel pin into the bore and I certainly can't get behind tapered "range rods." Conversely, I can't see a disadvantage to letting an indicator ball walk over the lands.

According to the inspection I've done. a burred edge will shoot off differently than a clean, pulled-back edge. I realize the lands all show some pull-off but they're all similar and all on the side.

But then I'm one of those guys who think the crown is important.

My Opinion

al
Click to expand...

Al
Do you remove the area where the indicator probe scored the bore?
 
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