Barrel Indexing and Barrel Nut

[Eddie Harren]

"Is headspace that critical not really. Larry"

Not if some other fool is pulling the trigger!

 

[Uthink Uknow]

You have a private message, Eddie.

 

[Cool Tool]

I was reading this thread and a response by Trevor (screen name Hengehold), and it got me to wondering about a potential downside of a barrel nut design.

http://forum.accurateshooter.com/threads/indexing-a-rifle-barrel.3902203/

Bottom line, with a barrel nut, the barrel is screwed in until headspace is correct, and then a jam nut is used to keep the barrel locked to the receiver. There is no "indexing" of the bore curvature to 12 o'clock or 6 o'clock. The bore curvature "plane" is just where it happens to land, at any possible "o'clock" position. Correct?

With a conventional barrel shoulder design, the gunsmith can chamber and machine the barrel so that when it is fully secured into the action, the barrel bore curvature can be oriented where ever the smith wants it.

Am I misunderstanding or missing something?

Phil

Trevor's comments.

"...Great question. The Long answer to your short question is that indexing a barrel in a 12 o'clock or 6 o'clock position is giving it The best possible state of harmonics to start with.

To illustrate what is happening you can try an exercise with a cleaning rod secured near the handle in a vice. First, Flick the end of the cleaning rod straight up-and-down and watch the pattern of movement of the tip of the cleaning rod until movement comes to a stop. second, try flicking the cleaning rod left and right and watch the pattern of movement of the cleaning rod until the mvmt has come to a stop. You will notice that when you flick the cleaning rod in an up-and-down motion that as the cleaning rod eventually stops whipping up and down it stays in a vertical plane. However, when you flick the cleaning rod in a lateral motion you'll notice that before it comes to rest the whip pattern of the cleaning rod is lateral then circular before eventually making a vertical motion. This cleaning rod is representing the action of a barrel that is whipping while being shot. A barrel that is whipping only in a vertical plane would have only one movement to overcome. A barrel with a lateral movement would eventually have to overcome not just the lateral movement but a circular motion and eventually a vertical mvmt as you will see demonstrated with a cleaning rod.The idea of indexing a bore in the 12 o'clock or 6 o'clock positions can be tested and realized with a barrel mounted rest.

If you were to place a barreled action in a rest and shoot groups rotating 90° after each group you will find that the barrel will shoot groups in a different location for each 90° rotation. In other words the point of impact will change on paper each time you rotate the barrel. At 100 yds I would typically see a point of impact shift of several inches per 90 degree rotation. Additionally, you will find that the groups in the 12 o'clock and 6 o'clock positions will be smaller groups than the groups found in the 3 o'clock and 9 o'clock areas. I have conducted this experiment with about a dozen different smallbore barrels and I have never seen a barrel that did not shoot it's best groups in the 12 o'clock and 6 o'clock positions. The difference in group sizes that I experienced was that the 12 o'clock and 6 o'clock groups would consistently be around half the size of the lateral groups found in the 3 o'clock and 9 o'clock positions. This was true of all ammunition tested from the high dollar Lapua and Eley to the lower-priced SK and Wolf ammunition.

As a sidenote, the rest that I used was a barrel mounted fixture that could absorb some recoil and return to battery in the same position every time and was mounted onto a mill and shot at 100 yards.

This practice of barrel indexing is primarily useful in smallbore where tuning the ammunition to the rifle is not an option. I have conducted the same experiment with high-powered rifles but the rest that I have does not handle the recoil as well as smallbore rifles. When I conducted this experiment with a couple of high-powered rifles I did see similar results as the barreled action was rotated in which the groups found in a vertical plane such as the 12 o'clock and 6 o'clock positions were the smallest groups and the groups found in a lateral plane at the 3 o'clock and 9 o'clock positions were the biggest groups.

My experience with bore indexing has been a trial and error method rather then a measure and cut method. Without conducting a trial and error approach, one would never see the resulting reduction in group sizes for the 12 o'clock and 6 o'clock positions . .

Sorry for the dissertation but I have a unique amount of experience with testing indexed barrels. I hope this helps.

-Trevor...".

I was reading this thread and a response by Trevor (screen name Hengehold), and it got me to wondering about a potential downside of a barrel nut design.

http://forum.accurateshooter.com/threads/indexing-a-rifle-barrel.3902203/

Bottom line, with a barrel nut, the barrel is screwed in until headspace is correct, and then a jam nut is used to keep the barrel locked to the receiver. There is no "indexing" of the bore curvature to 12 o'clock or 6 o'clock. The bore curvature "plane" is just where it happens to land, at any possible "o'clock" position. Correct?

With a conventional barrel shoulder design, the gunsmith can chamber and machine the barrel so that when it is fully secured into the action, the barrel bore curvature can be oriented where ever the smith wants it.

Am I misunderstanding or missing something?

Phil

Trevor's comments.

"...Great question. The Long answer to your short question is that indexing a barrel in a 12 o'clock or 6 o'clock position is giving it The best possible state of harmonics to start with.

To illustrate what is happening you can try an exercise with a cleaning rod secured near the handle in a vice. First, Flick the end of the cleaning rod straight up-and-down and watch the pattern of movement of the tip of the cleaning rod until movement comes to a stop. second, try flicking the cleaning rod left and right and watch the pattern of movement of the cleaning rod until the mvmt has come to a stop. You will notice that when you flick the cleaning rod in an up-and-down motion that as the cleaning rod eventually stops whipping up and down it stays in a vertical plane. However, when you flick the cleaning rod in a lateral motion you'll notice that before it comes to rest the whip pattern of the cleaning rod is lateral then circular before eventually making a vertical motion. This cleaning rod is representing the action of a barrel that is whipping while being shot. A barrel that is whipping only in a vertical plane would have only one movement to overcome. A barrel with a lateral movement would eventually have to overcome not just the lateral movement but a circular motion and eventually a vertical mvmt as you will see demonstrated with a cleaning rod.The idea of indexing a bore in the 12 o'clock or 6 o'clock positions can be tested and realized with a barrel mounted rest.

If you were to place a barreled action in a rest and shoot groups rotating 90° after each group you will find that the barrel will shoot groups in a different location for each 90° rotation. In other words the point of impact will change on paper each time you rotate the barrel. At 100 yds I would typically see a point of impact shift of several inches per 90 degree rotation. Additionally, you will find that the groups in the 12 o'clock and 6 o'clock positions will be smaller groups than the groups found in the 3 o'clock and 9 o'clock areas. I have conducted this experiment with about a dozen different smallbore barrels and I have never seen a barrel that did not shoot it's best groups in the 12 o'clock and 6 o'clock positions. The difference in group sizes that I experienced was that the 12 o'clock and 6 o'clock groups would consistently be around half the size of the lateral groups found in the 3 o'clock and 9 o'clock positions. This was true of all ammunition tested from the high dollar Lapua and Eley to the lower-priced SK and Wolf ammunition.

As a sidenote, the rest that I used was a barrel mounted fixture that could absorb some recoil and return to battery in the same position every time and was mounted onto a mill and shot at 100 yards.

This practice of barrel indexing is primarily useful in smallbore where tuning the ammunition to the rifle is not an option. I have conducted the same experiment with high-powered rifles but the rest that I have does not handle the recoil as well as smallbore rifles. When I conducted this experiment with a couple of high-powered rifles I did see similar results as the barreled action was rotated in which the groups found in a vertical plane such as the 12 o'clock and 6 o'clock positions were the smallest groups and the groups found in a lateral plane at the 3 o'clock and 9 o'clock positions were the biggest groups.

My experience with bore indexing has been a trial and error method rather then a measure and cut method. Without conducting a trial and error approach, one would never see the resulting reduction in group sizes for the 12 o'clock and 6 o'clock positions . .

Sorry for the dissertation but I have a unique amount of experience with testing indexed barrels. I hope this helps.

-Trevor...".

I hate to tell you if your bore has to be indicated to 6 oclock or 12 oclock you don't have a very straight barrel.

 

[savagedasher]

I hate to tell you if your bore has to be indicated to 6 oclock or 12 oclock you don't have a very straight barrel.

Some I have see is over 100 thousands .
Larry

 

[Cool Tool]

Some I have see is over 100 thousands .
Larry

You mean to tell me you have seen a 1/10 of an inch of runout from one end to the other.

 

[Cool Tool]

have seen barrels that the hole did not look straight straightened the hole ground the barrel between centers an that hole was only 4 thousands out from one end to the other.

 

[savagedasher]

You mean to tell me you have seen a 1/10 of an inch of runout from one end to the other.

No I saying the bore isn't straight . Larry

 

[Phil3]

No I saying the bore isn't straight . Larry

Please see

It looks to me that the chamber end of the barrel bore is straight, as measured by a test indicator at the extreme end and a couple inches in. But with that end dialed in, the muzzle end wobbles around to the tune of .075" runout. This would indicate a banana shaped bore. But, the barrel itself also wobbles in concert with the bore. If the barrel external surface wobbles .075", then it would appear the entire barrel (barrel AND bore) are banana shaped (bent).

If this barrel was chambered where there was no external runout on the barrel at either end, then would not the chamber end bore be slightly off angle from the bore, thereby causing the reamer to run in at a slight angle to the bore? How much that affects accuracy, I've no idea.

My $0.02, but I am not gunsmith.

Phil

 

[savagedasher]

Please see

It looks to me that the chamber end of the barrel bore is straight, as measured by a test indicator at the extreme end and a couple inches in. But with that end dialed in, the muzzle end wobbles around to the tune of .075" runout. This would indicate a banana shaped bore. But, the barrel itself also wobbles in concert with the bore. If the barrel external surface wobbles .075", then it would appear the entire barrel (barrel AND bore) are banana shaped (bent).

If this barrel was chambered where there was no external runout on the barrel at either end, then would not the chamber end bore be slightly off angle from the bore, thereby causing the reamer to run in at a slight angle to the bore? How much that affects accuracy, I've no idea.

My $0.02, but I am not gunsmith.

Phil

Please see

It looks to me that the chamber end of the barrel bore is straight, as measured by a test indicator at the extreme end and a couple inches in. But with that end dialed in, the muzzle end wobbles around to the tune of .075" runout. This would indicate a banana shaped bore. But, the barrel itself also wobbles in concert with the bore. If the barrel external surface wobbles .075", then it would appear the entire barrel (barrel AND bore) are banana shaped (bent).

If this barrel was chambered where there was no external runout on the barrel at either end, then would not the chamber end bore be slightly off angle from the bore, thereby causing the reamer to run in at a slight angle to the bore? How much that affects accuracy, I've no idea.

My $0.02, but I am not gunsmith.

Phil

Phil
When I talk index I'm talking is timing the bore end wobble to be at 12 or 6 . If you want the out straigh it would need to be done with a center less grinder . Larry

 

[Cool Tool]

Phil
When I talk index I'm talking is timing the bore end wobble to be at 12 or 6 . If you want the out straigh it would need to be done with a center less grinder . Larry

Well it is obvious that you gurus are trying to twist what I am saying is wrong I guess I have been doing it wrong for the last 30 plus years you do it your way I will do it my way if I had a barrel that had that much runout I would have sent it back

 

[savagedasher]

Well it is obvious that you gurus are trying to twist what I am saying is wrong I guess I have been doing it wrong for the last 30 plus years you do it your way I will do it my way if I had a barrel that had that much runout I would have sent it back

Sent several back the bore was crooked as a snake . I never said your wrong. I like mine done with two sets of spiders with a rod in the end that I'm working with . 4 " in the bore and 4 out . With the exposed end being Zero the whole distance . Where the other end of the barrel is don't matter if the rod is zero . But that is how I time it . Larry

 

[Eddie Harren]

Sent several back the bore was crooked as a snake . I never said your wrong. I like mine done with two sets of spiders with a rod in the end that I'm working with . 4 " in the bore and 4 out . With the exposed end being Zero the whole distance . Where the other end of the barrel is don't matter if the rod is zero . But that is how I time it . Larry

Clear as mud!

 

[hogpatrol]

 

[madderg]

Larry is right, that's how you thread and chamber a barrel. The only thing I have seen that indexes as stated in the beginning of this post is a golf club shaft. It does work well on a golf shaft if you can find the oscillation and set the club face so it's lined up with the 6 and 12. Helps keep your shots centered.

 

[savagedasher]

Larry is right, that's how you thread and chamber a barrel. The only thing I have seen that indexes as stated in the beginning of this post is a golf club shaft. It does work well on a golf shaft if you can find the oscillation and set the club face so it's lined up with the 6 and 12. Helps keep your shots centered.

I'm not saying it is right but that is how I want Mine done . Larry

 

[Cool Tool]

Please see

It looks to me that the chamber end of the barrel bore is straight, as measured by a test indicator at the extreme end and a couple inches in. But with that end dialed in, the muzzle end wobbles around to the tune of .075" runout. This would indicate a banana shaped bore. But, the barrel itself also wobbles in concert with the bore. If the barrel external surface wobbles .075", then it would appear the entire barrel (barrel AND bore) are banana shaped (bent).

If this barrel was chambered where there was no external runout on the barrel at either end, then would not the chamber end bore be slightly off angle from the bore, thereby causing the reamer to run in at a slight angle to the bore? How much that affects accuracy, I've no idea.

My $0.02, but I am not gunsmith.

Phil

Did you look through this barrel before you started this project.

 

[savagedasher]

Here is my take Gun barrels are drilled with about a 40" drill the barrel is turned or the drill is . The cutting head is is fastened to a rod and sharpen to where it cuts true to the rod . The bore is cut undersized and honed for diameter The reason for honeing the drill doesn't cut sraight . Honing will straighten some imperfections but not all . Cut rifeling does not induce stress on the barrel . So the barrel is rifeling is the same even with the not being straight .
Button rifeling is done with pressure and it does bend the barrel . They some times Get straighten by hand but always get heat treatment to relieve the stress from the button process.
More then likely both barrel are not straight .
When you index a barrel you take Around 4" ove it and indext it straight My preference is with a rod . By using a rod you not only use 4" of the barrel but the inches it sticks out.
Using 2 sets of spiders and the head stock of the lathe The end of the barrel your going to machine is straight in the head stock of the lathe. The movement on the other end is what you're timing or indexting . With a shoulder or a nut the barrel must be aimed in the same direction . Larry

 

[savagedasher]

I believe there may be little difference. I indicate only the side I am working on, the first 3" of bore. I rarely will see over .015" bore runout at the muzzle on a 31" blank. I will time that up or down. How much difference would it make if you indicated the throat and muzzle? I dont think we could see a difference. I think if your seeing a lot of runout at the muzzle, like .100" you are bending the barrel in your setup, very easy to do by the way. Also throw those tapered rods in the trash, they dont repeat and if you go in with a long reach indicator you will be surprised to see how much runout there is in the bore after using those.

Been there done that taper rods with bushings works great . Yes I have seen .100 run out and they were sent back. Simple light test Normally tell you if their straight . It has Been use for ever with arrow shafts and gun barrels . Larry

 

[Cool Tool]

Been there done that taper rods with bushings works great . Yes I have seen .100 run out and they were sent back. Simple light test Normally tell you if their straight . It has Been use for ever with arrow shafts and gun barrels . Larry

When you have seen a 100thousands did you visually inspect the bore by casting off of a light were you can pic up all the light rings coming back at you if the hole is banana shape a 100 thousands you would only be able to see one third of the hole.

 

[savagedasher]

When you have seen a 100thousands did you visually inspect the bore by casting off of a light were you can pic up all the light rings coming back at you if the hole is banana shape a 100 thousands you would only be able to see one third of the hole.

I never said anything about rings but I know you understand . Hell to be old . Larry