Comments

1. On March 8, 2021 at 11:08 am, John said:

   Can it? 2 words: “Wandering Zero”.

2. On March 8, 2021 at 11:11 am, Herschel Smith said:

   My best bet without studying it more would have been that the zero is basically unaffected but the groups open up.

3. On March 8, 2021 at 3:21 pm, John said:

   @Herschel
   Hello! I think it depends much on each individual rifle. Many seem almost unnaffected.
   Of course we know that steel expands with heat and shrinks as it cools.
   This movement in a barrel must be even more complicated due to the hole,
   rifling and manufacturing stresses from such processes as hammer forging.
   I have owned or shot several firearms using their iron sights that would fire very
   accurately for the first several shots and then the point of impact would move about as
   they heated from more shots being fired. Wind was not an element as the ranges were
   quite short and the guns were fired from prone position or a bench. The only change in the elements involved in firing was the barrels heating. I do not think enough shots were fired to bring barrel leading into the picture. Once the barrels cooled to ambient temperature they
   returned to their original zero.The heat may have caused them to put different points of
   pressure against the stocks but it was the heat that caused the “wandering”.
   I believe that Cyro treatments, where extreme heat and cold are applied have been used
   for used for years to normalize the manufacturing stresses in some barrels with heat and
   stress movement issues with quite a bit of success. I understand that there are many and
   varied beliefs on this point but my experiences have convinced me of my opinion.

4. On March 8, 2021 at 4:32 pm, =TW= said:

   What John^^ said. Stress relieving couldn’t hurt.
   I reckon concentricity will be a factor as well.

5. On March 8, 2021 at 4:50 pm, Herschel Smith said:

   Okay, so let’s take a step up in engineering complexity.

   Problem posed: A barrel, with of course all of the crystalline structures, grain boundaries, etc., along which stress propagates, like metal should be. In other words, a typical metal, not a theoretical metal posed for the purpose of a toy problem.

   Now. Given the following stipulations – EXACTLY the same grains of powder, EXACTLY the same bullet weight, EXACTLY the same roundness of the bullet, EXACTLY the same center of gravity of the bullet, EXACTLY the same temperature, and everything else.

   Consider the case of perfect aim (or near-perfect), as would be the case with a machine-held firearm. Will the bullet impact be EXACTLY the same on a target (in other words, will the bullet go through the same hole), or will stress propagation follow along different grain boundaries and crystalline boundaries every time the firearm is discharged, more like a Monte Carlo (stochastic) function?

   Another way of posing the problem is: Is the natural frequency of the barrel a deterministic or a stochastic model?

   Consider Brownian motion in your answer, along with any other relevant atomic level phenomena.

6. On March 8, 2021 at 5:08 pm, Bill Sullivan said:

   If he was referring to Privi Partizan ammo, I had excellent, match grade results in a Stag AR with their .223 70 grain ammo. And poor results with Lake City 62 grain green tip. Your twist rate may have quite an effect on the group size, too. Mine is a 1/9″ twist.

7. On March 8, 2021 at 7:18 pm, John said:

   I’m afraid the limit of my engineering education stops after I was taught to properly pronounce
   Molybdenum, but I’ll give it a “shot” and try to dance a few steps.
   I think I go with stochastic model for the natural frequency of the barrel. Every shot fired, regardless of the perfection of the ammunition and temperatures, causes miniscule barrel changes, so I will apply the “to use it is to abuse it” school of thought and say any wear will have
   an effect on the accuracy of each shot. As to determinism; it would seem to be excluded without the non-random elements it needs. Also, Brownian motion and determinism seem to be in entirely different camps. I think determinism looks more at home with money than machinery.
   The properties of the steel, inclusive of its atomic, molecular structure and grain formation that I recognize as being critical to that particular metal, are in my engineering untrained mind,
   “all of a piece” and I will not attempt to go there.
   As to my previously stated opinion based on my limited but actual experience?
   It remains unchanged.

8. On March 8, 2021 at 7:49 pm, Herschel Smith said:

   @John,

   “Deterministic.” As in able to be modeled exclusively with a set of closed-form equations and get the right answer in every instance. Or if not solvable, capable of being solved by numerical techniques and get the right and SAME answer each and every time.

9. On March 8, 2021 at 8:58 pm, Uncle Al said:

   My intuition is that it is stochastic, because otherwise I would have to assume that the barrel’s metallic grain and crystalline boundaries remain absolutely fixed even after undergoing the stresses involved in each discharge, not to mention thermal expansion/contraction cycles. If they are not at all changed, then I assume that stress propagation MUST “follow along different grain boundaries and crystalline boundaries every time.”

10. On March 8, 2021 at 9:01 pm, Geoff said:

    Who but the Military shoots thousands of rounds in a training mission or war? Of course that will have an effect, but the average shooter at the range may only go through 20 to 100 rounds over period of hours. It’s not like you’re going to get the barrel too hot to touch.
    In fact, the first few shots as “cold barrel” will be worse for accuracy than a warm barrel.
    Just my experience.

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