Indexing a rifle barrel...

[savagedasher]

So you have range rods in the chamber and muzzle ends and are indicating off of these, correct? And when the muzzle end is off by a certain amount you mark that point on the battle and then use that for the 12 or 6 o'clock position?

Yes but the chamber end must be machined and the head space correct where the muzzle is at 6 or 12 . Larry

 

[Tim Singleton]

If you can't take the action out of the stock. You have to machine a threaded collar to simulate the action. Take an old barrel mark it at 12o'clock when on the action screw it in the collar mark the collar
Now you have a tool to index future barrels to that action

 

[RoscoXR]

Ok excuse my ignorance,.but when I think of the muzzle I understand it to be part of the barrel where the bullet exits. A complete 360 degree section, where the rifling ends and a crown is typically added. I don't understand what is at the 12o'clock position? I think I am misunderstanding what the "muzzle" is in the context of the conversation.

In one of your previous posts you stated if the muzzle were 0.005 or less then no need to bother which lead me to believe it had something to do with the inner diameter measurements.

 

[BoydAllen]

For purposes of this explanation, imagine that the bore of a barrel is a long continuous curve. Then imagine that you are setting this barrel up through the headstock so that the bore of the end that is being threaded and chambered is a close to coaxial with the rotational axis of the headstock as your equipment will allow, over a length of say 2 1/2" inches or more. Since the barrel is slightly curved, the only way to do this is to adjust the spider on the outboard end of the lathe is holding the CL of the muzzle end of the barrel offset from the CL of the headstocks's axis of rotation. This setup is entirely different than zeroing in both ends of the barrel. Depending on the amount that the bore curves, the muzzle end must be offset in order to achieve the desired alignment at the breech end. When the posters have referred to clocking a barrel, they are referring to the direction of the offset relative to the action, with the rifle sitting level. Not all smiths agree with this chambering setup, but I think that it is fair to say that different methods have produced winning barrels. The thought behind having the barrel clocked at 6:00 or 12:00 is that any straightening of the bore under the pressure of firing would be in the vertical plane, rather than inducing undesirable horizontal motion.

 

[Tim Singleton]

Sitting behind the rifle at the bench looking down the top of the rifle
Top dead center of the barrel is to me 12oclock

If you chamber by indicating the throat area in and the aft section of the barrel the muzzle will ru out. Whether you use rods or indicators you mark the high spot of the run out on the muzzle. Then chamber and head space you barrel to index the muzzle swing to the 12oclock position

 

[savagedasher]

Ok excuse my ignorance,.but when I think of the muzzle I understand it to be part of the barrel where the bullet exits. A complete 360 degree section that is machined. I don't understand what is at the 12o'clock position? I think I am misunderstanding what the "muzzle" is.

The muzzle end is the front end where the bullet exits yes.
With the chamber end is dialed in true to the bore . The muzzle end normally is off center to breach end . Rotate the barrel and the lathe head you will see the off center circle it makes . You chamber to the action to where the muzzle movement is at 12 or 6.
If you go to Gordy Gritter chambering he has a video explaining it.
The process is done through the head stock in a lathe . With each end of the barrel being he'd separate from each other . Larry

 

[Tim Singleton]

For purposes of this explanation, imagine that the bore of a barrel is a long continuous curve. Then imagine that you are setting this barrel up through the headstock so that the bore of the end that is being threaded and chambered is a close to coaxial with the rotational axis of the headstock as your equipment will allow, over a length of say 2 1/2" inches or more. Since the barrel is slightly curved, the only way to do this is to adjust the spider on the outboard end of the lathe is holding the CL of the muzzle end of the barrel offset from the CL of the headstocks's axis of rotation. This setup is entirely different than zeroing in both ends of the barrel. Depending on the amount that the bore curves, the muzzle end must be offset in order to achieve the desired alignment at the breech end. When the posters have referred to clocking a barrel, they are referring to the direction of the offset relative to the action, with the rifle sitting level. Not all smiths agree with this chambering setup, but I think that it is fair to say that different methods have produced winning barrels. The thought behind having the barrel clocked at 6:00 or 12:00 is that any straightening of the bore under the pressure of firing would be in the vertical plane, rather than inducing undesirable horizontal motion.

I have chambered a few barrels for myself prior to indexing them. As I went thru normal seating depth testing I would see a lot more horizontal in the load testing than I do now after I have began indexing them at 12o'clock

 

[savagedasher]

I have chambered a few barrels for myself prior to indexing them. As I went thru normal seating depth testing I would see a lot more horizontal in the load testing than I do now after I have began indexing them at 12o'clock

I like mine at 12 for shooting longer range.
Larry

 

[RoscoXR]

Thanks to everyone that contributed, I think I finally wrapped my head around it!!

 

[hoz53]

For purposes of this explanation, imagine that the bore of a barrel is a long continuous curve. Then imagine that you are setting this barrel up through the headstock so that the bore of the end that is being threaded and chambered is a close to coaxial with the rotational axis of the headstock as your equipment will allow, over a length of say 2 1/2" inches or more. Since the barrel is slightly curved, the only way to do this is to adjust the spider on the outboard end of the lathe is holding the CL of the muzzle end of the barrel offset from the CL of the headstocks's axis of rotation. This setup is entirely different than zeroing in both ends of the barrel. Depending on the amount that the bore curves, the muzzle end must be offset in order to achieve the desired alignment at the breech end. When the posters have referred to clocking a barrel, they are referring to the direction of the offset relative to the action, with the rifle sitting level. Not all smiths agree with this chambering setup, but I think that it is fair to say that different methods have produced winning barrels. The thought behind having the barrel clocked at 6:00 or 12:00 is that any straightening of the bore under the pressure of firing would be in the vertical plane, rather than inducing undesirable horizontal motion.

Hi Boyd. So if you index your barrel you are pointing the barrel itself in a certain direction but how do we know if the bore is pointing in the same direction since we know the bore is not running true with the barrel? Hope you are doing well these days.

 

[BoydAllen]

When gunsmiths index, it is usually done in conjunction with chambering through the headstock, and setting the barrel up entirely off of readings from the chamber end, which typically results in the muzzle of the barrel off center in the spider that is used to support the barrel at the outboard end of the spindle. Even when the method involves zeroing both ends of the barrel, smiths have told me that an internal curve may be observed by careful observation, looking through the barrel while rotating the spindle by hand.

Years ago, I had a number of interesting conversations with a fellow who manufactured custom bolt action pistols for silhouette shooters. He told me that his practice had been to buy untapered rifle blanks and to cut them in half to make two pistol barrels. He told me that he thought that people would be surprised at the amount of bore offset that was in the middle of the rifle blanks, even though it was centered in both ends, as much as .035. These were name brand, top grade barrels, and he also told me that in his experience the cut barrels were better in this regard. This was in the late 90s. His name was John Illum, and his company was Rampro. We also discussed some of the features of his actions, and I believe that they had, and still do have some merit.

 

[Nvreloader]

Boyd Allen and Guys,
Does anyone know for sure, when indexing to any points,

How far the groups move from POA,
Several hundreds of an inch, OR inches from POI?

Meaning the bbl was aimed a a certain point,
and the groups POI landed .xyz " from POA?

Are we talking about great amounts, like inches?

Yes, I realize that depends on the curve of the bbl etc.

Tia,
Don

 

[butchlambert]

Boyd Allen and Guys,
Does anyone know for sure, when indexing to any points,

How far the groups move from POA,
Several hundreds of an inch, OR inches from POI?

Meaning the bbl was aimed a a certain point,
and the groups POI landed .xyz " from POA?

Are we talking about great amounts, like inches?

Yes, I realize that depends on the curve of the bbl etc.

Tia,
Don

Everybody talks curve. Maybe you might think spiral.

 

[Tim Singleton]

Boyd Allen and Guys,
Does anyone know for sure, when indexing to any points,

How far the groups move from POA,
Several hundreds of an inch, OR inches from POI?

Meaning the bbl was aimed a a certain point,
and the groups POI landed .xyz " from POA?

Are we talking about great amounts, like inches?

Yes, I realize that depends on the curve of the bbl etc.

Tia,
Don

I think as you know the out come will vary greatly from barrel to barrel and caliber to caliber

Do some testing of your own and report back

 

[savagedasher]

I have thought it out and mine will be timed up. Larry

 

[Eddie Harren]

I have thought it out and mine will be timed up. Larry

"at 12 for longer range".

 

[butchlambert]

And I will continue to indicate mine to where both ends are concentric to the lathe spindle axis.

 

[Nvreloader]

Tim
If I knew that answer, I would have not posted any info,
to obtain some info..

I read the article on the CF/RF groups that were posted by
Gene Biggs and Mike Ross etc.

What I did NOT find,
was the amount of difference between the POA and POI for the RF groups, due to INDEXING the bbl.

I have a chance to index a 17 WSM caliber RF bbl, and was wondering if the effort was worth the results........ etc.

Tia,
Don

I think as you know the out come will vary greatly from barrel to barrel and caliber to caliber

Do some testing of your own and report back

 

[Tim Singleton]

Tim
If I knew that answer, I would have not posted any info,
to obtain some info..

I read the article on the CF/RF groups that were posted by
Gene Biggs and Mike Ross etc.

What I did NOT find,
was the amount of difference between the POA and POI for the RF groups, due to INDEXING the bbl.

I have a chance to index a 17 WSM caliber RF bbl, and was wondering if the effort was worth the results........ etc.

Tia,
Don

I don't think you would see anything measurable with a 17 wsm.
IMO The entire rifle system including rest and wind flags would have to be in the extreme accuracy level to ever be able to see on the target any change from indexing. Even at that some barrels don't show as much of a change in poi as others on the same platform. They just don't.

 

[Nvreloader]

Guys
I finally found the answer to my question,
How far does the POA and POI change,
due to indexing the bbl.

Per info from Mike Ross's articule,
POA and POI can change as much as 2" or more at 50yds,
due to bbl indexing around the clock face positions.

Tia,
Don