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...".
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...".
....so I would have to settle on a rotation that gets me the best compromise between safe HS and barrel indexing. Vertical indexing could be reliably accomplished for a drop in if the dimensions of the receiver/bolt face would have very precise manufacturing tolerances hit for each unit made and that would be unlikely short of a full custom action. Accidents do happen and one might get lucky however. I am not aware that drop in barrel makers are trying to index their products. Someone correct me if I am wrong.
