What is wrong?

[CFJunkie]

Technically it is the speed of transmission of a shock wave in the barrel steel (since the s1ound waves of the blast propagate through the air) but the analogy of transmission is a good one.
The speed varies with the medium that the shockwave propagates through (the steel alloy in the barrel steel) while the speed of sound varies with the medium that sound wave propagates through - air, water, etc.
The caliber doesn't make a difference to the reflection time, only the steel of the barrel (and of the flash hider, muzzle brake, or suppressor if they are attached to the barrel).
The shock wave propagation is in the steel not the bore.

The propagation velocity in steel is between just under 19,000 fps and just over 20,000 fps (depending upon the alloy) while the nominal velocity of sound is from around 1100 to 1150 fps depending upon the temperature.
Air is a lot less dense than steel.
A 24-inch Savage barrel with 0.3% barrel-steel has a shock wave reflection time to go from chamber to muzzle of 0.1046 msec. It would take another 0.1046 to get back to the chamber (2nd reflection).
In that case, the bullet would accelerate from 0 to 2,500 fps in the length of the barrel, let's say 2 feet or 24 inches.
The muzzle velocity of the bullet and time in the barrel depends on the type of powder, powder charge, bullet seating depth and trim length of the load.
With a difference of almost 17x in velocity between wave propagation in steel and sound wave propagation in air, the reflection would go back and forth from 5 to 6 times from chamber to muzzle and back to chamber before the sound reached the muzzle or the bullet left the muzzle.
It would take about 1.1 to 1.3 ms for the bullet to exit the muzzle, depending on the barrel length and the steel alloy, assuming the absence of a muzzle brake.
It would take about 1.74ms for the sound to reach the muzzle at the end of a 24-inch barrel.
The bullet would be well out of the barrel and on its way down range before the sound arrived at the end of the barrel.

[charlie b]

Yep, speed of sound in steel is the technical term. Common term used in explosives testing (and high power laser effects testing). And, yes, it varies with the density of the material, even in different alloys of steel or in other metals, or in liquids or gasses. Higher density means faster travel of the shock wave, which is why it is so much faster in steel than it is in air.

[Dave Hoback]

Exactly why I shoot down the idea of people talking about “loading for the bullet to exit on the number “x” reflection at 1.02m/s” -:blah::blah:blah. I started picking up on this several years ago. Then I started wondering, are these people using filming equipment that can accurately capture 20K FPS reactions? And overlap software to correlate the top/bottom of reflection to the actual timing in M/S? The answer is, of course they don’t. It simply finding the published data of such & such a metal and the reflection numbers exhibited when a certain load is fired through it. It’s already established numbers we can easily find online. Basically it’s no different than simply saying “I’m load “x” grains of “y” powder and hoping for “z” velocity.

So why then do some continue to use the loading for reflection speak? Because it makes you sound really, really, ​SMART! LOL!

[Ernest T]

Exactly why I shoot down the idea of people talking about “loading for the bullet to exit on the number “x” reflection at 1.02m/s” -:blah::blah:blah. I started picking up on this several years ago. Then I started wondering, are these people using filming equipment that can accurately capture 20K FPS reactions? And overlap software to correlate the top/bottom of reflection to the actual timing in M/S? The answer is, of course they don’t. It simply finding the published data of such & such a metal and the reflection numbers exhibited when a certain load is fired through it. It’s already established numbers we can easily find online. Basically it’s no different than simply saying “I’m load “x” grains of “y” powder and hoping for “z” velocity.

So why then do some continue to use the loading for reflection speak? Because it makes you sound really, really, ​SMART! LOL!

Yeah, I have no idea what that's about or if its even a real thing you can master.

[charlie b]

I think you can, and we all actually do it without measuring it. It is called a velocity ladder. You shoot at several different loads and pick the one with the best accuracy. Above and below that point a little and the group opens up.

The guys who wrote an article on it a few years ago postulated that the traveling wave causes the barrel to slightly increase and decrease in dia. If the bullet exits during the 'large' portion of the node it was less accurate. If it exits during the small node it is more accurate. So, they quantified what we had all been doing all along.

Before this people thought the nodes were from barrel whip, which is totally different. And, it happens after the bullet leaves the barrel.

CFJunkie has shown that using the software to determine exit times severely reduces the amount of shooting needed to find a node. His groups reflect that.

IMHO, this is what good science is all about. But, I am a bit biased cause half my career was as a test engineer. Most of that time was spent trying to figure out what is making things go wrong.

[PhilC]

Well said Charlie, and all anyone needs to do is search CFJunkie's posts to read about exit timing tuning for accuracy.

[South Prairie jim]

I think you can, and we all actually do it without measuring it. It is called a velocity ladder. You shoot at several different loads and pick the one with the best accuracy. Above and below that point a little and the group opens up.

The guys who wrote an article on it a few years ago postulated that the traveling wave causes the barrel to slightly increase and decrease in dia. If the bullet exits during the 'large' portion of the node it was less accurate. If it exits during the small node it is more accurate. So, they quantified what we had all been doing all along.

Before this people thought the nodes were from barrel whip, which is totally different. And, it happens after the bullet leaves the barrel.

CFJunkie has shown that using the software to determine exit times severely reduces the amount of shooting needed to find a node. His groups reflect that.

IMHO, this is what good science is all about. But, I am a bit biased cause half my career was as a test engineer. Most of that time was spent trying to figure out what is making things go wrong.
I don’t subscribe to the bulging snake swallowing an egg theory at all, barrel whip to a degree- yes ,barrel/exit timing - yes

[Blue Avenger]

Had a very consistent 6mm Rem chambered barrel, Mauser custom. Second shot 3" higher. Third shot 1.5" higher. 3/4" Higher for the 4th. Then it would group about 1" around the 4th shot.

[charlie b]

I don't really know what the 'effect' is. The idea of nodes have been around a long time and they do seem to correlate with the resonance theory. Just don't really know how the resonance is changing the bullet path. It is a symmetrical effect, ie, the barrel doesn't really move, unless there is a residual stress or some other flaw in the barrel. It does seem to be noticed by an inconsistency in muzzle velocity when not 'on' a node.

This is different than barrel whip, which is the result of the bullet travelling through the barrel. The artillery folks have researched this to death, mainly due to the long naval guns. They noticed that the barrel whip started when the projectile left the barrel (at least back in the 80's when I researched this). They had some really good high speed camera stuff, mainly using the relatively thin barrel of the Army's 175mm cannon.

[Robinhood]

I am guessing that all we need to do is listen to the people that do load workups for extreme accuracy and precision. What are top shooters saying about it? CF Junkie has in fact shown his results. It wouldnt be prudent to ask a flutist/flautist their opinion on retarded or advance cam timing on a 426 Hemi. Otherwise try a copper clean.

[charlie b]

The reason this hobby is so interesting is that we will probably never know why something works.

Such as, why does one barrel 'like' a particular bullet over another when both are the same weight and quality? And another barrel 'likes' the other bullet?

And, there is always the human element. If the shooter thinks one bullet should be better, does he shoot better with it just from his confidence in that component?

[South Prairie jim]

Weeding through the mis-information on line can be tough, better to just go out and test for one’s self.

when I get vertical or erratic shots, I fall back to an abbreviated charge ladder to ensure I’m solid in the node and no shifting, from there I can adjust my seating depth to hopefully get them to lay down.

[Robinhood]

Weeding through the mis-information on line can be tough, better to just go out and test for one’s self. when I get vertical or erratic shots, I fall back to an abbreviated charge ladder to ensure I’m solid in the node and no shifting, from there I can adjust my seating depth to hopefully get them to lay down. This is true. More so if you listen to people who have never worked up a proper load with the right components and the right tools.

[South Prairie jim]

This is true. More so if you listen to people who have never worked up a proper load with the right components and the right tools.

I would agree with you, we find that many guys stop when they come across a small group and do not complete the load development process. When tomorrows groups don’t repeat they struggle to understand why ?

[charlie b]

Yep. Every time I have tried to shortcut the process I end up going back and repeating the work up correctly.

[CFJunkie]

Another bit of information
(Sorry for the long post, but I think you need to see the results)

Last week I was reloading some 175 TMKs for my Savage 10 FCP-K .308 with IMR4064 powder.
I intended to load the rounds with a OAL of 2.890 to achieve an exit time of 1.345 msec and a mv of 2418 fps (my 10 FCP-K has a muzzle brake so the exit time is longer for the first 11 reflections).
Since I last loaded 168s I spun the micrometer die up a bit to be sure I didn't seat the first 175 too short.
I seated the first round and found that the dial caliber read 0.015so I adjusted the micrometer die back so it produced a OAL of 2.890.
But, I had been a bit overzealous in turning the die and was actually seating the bullets at 2.990 instead of 2.890. I never looked at the markings on the caliper slide that indicated that the first seating was as 3.015 instead of 2.915
My error resulted in an exit time of 1.386 msec. and a velocity of 2380 fps.

When I went to the range, and loaded the rounds, I managed to get the first 20 rounds seated (with some difficulty) and they fired. The remainder of the rounds would not allow the bolt to close.
In trouble shooting, I measured the rounds and found that they all had OALs of 2.990. I have still not figured out why some seated and some didn't.
The results with these rounds seated much longer than I intended were as follows:
5-round groups shot: 39.6 grs IMR4064 powder, seating depth 2.990, exit time 1.386 versus 1.345
0.330
0.374
0.477
https://connect.xfinity.com/appsuite/api/image/mail/picture?folder=default0%2FSent&id=769456&uid=02efb7fc603a47bb9438a369ff9c674c%40open-xchange.com
Average = 0.394
Median = 0.374
St Dev = 0.075


I brought the rounds home and reseated the remaining 28 to 2.890 and cleaned and resized the 20 brass that actually fired and reloaded them to the same spec.
5 round groups shot: 39.6 gr IMR4064 powder at 2.890 seating depth exit time 1.345 msec at 2418 fps.
0.332
0.333
0.381
0.387
Average 39.6 = 0.358
Median 39.6 = 0.357
St Dev 39.6 = 0.030

I had also an additional load with the same seating depth and exit time but loaded for increased temperature and a trim length that was 0.001 shorter.
5 round groups: 39.5 gr IMR 4064 powder at 2416 fps.
0.270
0.318
0.370
0.478
Average = 0.347
Median = 0.344
St Dev = 0.088


Combined Average = 0.352
Combined Median = 0.352
Combined St Dev = 0.049

Difference between the two exit times:


Difference 2.990 OAL at 1.386 msec. exit time versus combined 2.890 OAL at 1.345 msec. exit time
Difference In Exit time = 0.041 msec.
Difference In Average grp size = 0.041 inches in favor of the 1.345 msec. prescribed exit time.

The reflection difference for the mis-seated rounds was about 39% down the barrel toward the muzzle.
If the exit time was 0.10467 msec. larger so the reflection was at the muzzle instead of at the chamber, the average group size difference could have been between 0.090 to 0.100 inches.

[South Prairie jim]

Well I’m not the sharpest tool in the shop so I darn sure haven’t considered recording milliseconds to tune a 1000 yard Benchrest rifle. For some reason I’m not able to post any pictures of how we tune for 1 k but I think y’all might find it comforting to know that there is no Computor involved.
This link may or may not open up, this is a couple years of tuning for 1000 yard matches and if this helps anyone great.

https://www.thehighroad.org/index.php?threads/long-range-tuning.883884/

[wbm]

Thanks for the post.

Really enjoyed Varminterror's take on page 2.

"Into the madness indeed....OBT, magic velocity goals, velocity nodes, seating depth nodes, etc... none of it reconciles. But the Satterlee velocity curves, modified Newberry OCW targets, and long range Audette ladders all confirmed my charge weight node was holding, even though my velocity was changing a foot per second after every 4th round fired...but shooting small is easier than understanding WHY it shoots small."

[Dave Hoback]

Yeah…. This “exit time” malarky just seems to be “Look at Me” talk. But then, I haven’t shot 34,231 consecutive 1/4MOA groups, LOL! ;)

J/K.. I just couldn’t resist. :tea:

[South Prairie jim]

Thanks for the post.

Really enjoyed Varminterror's take on page 2.

"Into the madness indeed....OBT, magic velocity goals, velocity nodes, seating depth nodes, etc... none of it reconciles. But the Satterlee velocity curves, modified Newberry OCW targets, and long range Audette ladders all confirmed my charge weight node was holding, even though my velocity was changing a foot per second after every 4th round fired...but shooting small is easier than understanding WHY it shoots small."
Your welcome, I try to be helpful if I can.
When we superimpose the target( shoot at one point of aim) optimum barrel timing / exit timing seems a bit easier to interpret for myself, many of the methods are really just viewing from different angle, they reach or should reach the same conclusion.