Barrel Behaviour Theory

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!Peter!
Posts: 93
Joined: Sun Oct 30, 2016 6:35 am

Barrel Behaviour Theory

#1 Postby !Peter! » Wed May 30, 2018 1:24 pm

All,
In another thread I commented that I'd be happy to layout barrel behaviour theory as I see it. Subsequently, I see that williada is throwing out challenges.

I don't have the experience of others on this site in tuning a rifle but I have spent a bit of time digging into the physics to understand what is going on so that I can learn to tune a rifle faster.

What I'm intending on doing is to present some of the theory to understand what is going on and to correct some of the terminology commonly used which I believe makes this area more complicated than it needs to be.

The only thing that I ask is for people to use the correct terms in this thread. If you want to use a term incorrectly because it is commonly used incorrectly I ask that you put the term in " ", i.e. node vs "node". Using the correct terms will enable readers to search the net to learn more if they need or want to.

For people new to shooting, don't panic, you don't need to know this. This is about extracting the last bit of accuracy from the rifle.

While it helps to have done, and remember, high school physics, don't worry if you didn't it or can't remember it. You don't need to know the maths just the concepts and relationships.

To set the basic physics please read this online class on the physics of waves. Take particular attention to Lesson 3 and 4
http://www.physicsclassroom.com/class/waves

The next post I'll talk about what is causing the waves and the types of waves they cause.

I welcome all contributions and discussions.

AlanF
Posts: 6791
Joined: Wed Jun 15, 2005 8:22 pm
Location: Maffra, Vic

Re: Barrel Behaviour Theory

#2 Postby AlanF » Wed May 30, 2018 1:31 pm

Thank you Peter. Good idea. I'm looking forward to it.

Gyro
Posts: 349
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Location: New Zealand

Re: Barrel Behaviour Theory

#3 Postby Gyro » Wed May 30, 2018 3:38 pm

Jolly good idea Peter to be sure to be sure. Especially your reference to "setting the rules" for some discussion. After all most of us haven't been to university to study this stuff so it needs to be kept UNDERSTANDABLE.

If it's not understandable to us then it just might be BS ?

RDavies
Posts: 1911
Joined: Sun Feb 12, 2006 7:23 pm
Location: Singleton NSW

Re: Barrel Behaviour Theory

#4 Postby RDavies » Wed May 30, 2018 9:22 pm

Im keen to read about this sort of thing. I will likely stick to being an observer again though as I don't know the correct terminology for a lot of these things but am willing to learn more about it.
So far I,m enjoying the classroom physics/

Trevor Rhodes
Posts: 76
Joined: Mon Feb 03, 2014 8:31 pm

Re: Barrel Behaviour Theory

#5 Postby Trevor Rhodes » Wed May 30, 2018 10:38 pm

So what l learned from the youtube session on the spring is the the faster the vibrations the more or closer the nodes are. So does this relate to a faster bullet velosity down a barrel having more nodes than a slow one.

!Peter!
Posts: 93
Joined: Sun Oct 30, 2016 6:35 am

Re: Barrel Behaviour Theory

#6 Postby !Peter! » Wed May 30, 2018 10:45 pm

Gyro, you don't need a uni degree to understand this. If you want to get into the equations then a maths, science or engineering uni degree does help but you don't need to know the equations to understand the concepts and relationships.

RDavies, don't let not knowing the terminology hold you back from contributing.

!Peter!
Posts: 93
Joined: Sun Oct 30, 2016 6:35 am

Re: Barrel Behaviour Theory

#7 Postby !Peter! » Thu May 31, 2018 11:01 am

Trevor Rhodes wrote:So what l learned from the youtube session on the spring is the the faster the vibrations the more or closer the nodes are. So does this relate to a faster bullet velosity down a barrel having more nodes than a slow one.

Kudos to you for having the first stab at testing you understanding.

Short answer is no.

Questions for you to understand why: What type of standing wave is formed? What does it take for this standing wave to form? Then the final bit:How does the bullet's velocity initiate the formation of the standing wave?

Gyro
Posts: 349
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Location: New Zealand

Re: Barrel Behaviour Theory

#8 Postby Gyro » Fri Jun 01, 2018 4:15 am

Peter I'm not sure about where others here have got with thier studies but I'm planning to study lesson 3 tonight, having been thorough with my study of lessons 0, 1 and two over the last two nights.

I'm doing all the maths too as I go but I notice u say it's just an understanding of the concepts that is required to take us through this ? Regards Rob.

!Peter!
Posts: 93
Joined: Sun Oct 30, 2016 6:35 am

Re: Barrel Behaviour Theory

#9 Postby !Peter! » Fri Jun 01, 2018 6:02 am

If you do the maths that's great as it helps to understand it better but I don't think it is necessary to understand the concepts.

John T
Posts: 148
Joined: Sat Jan 07, 2006 5:42 pm
Location: Brisbane

Re: Barrel Behaviour Theory

#10 Postby John T » Fri Jun 01, 2018 5:16 pm

Hello Peter.

To what extent, if any, do the principles of standing wave patterns and harmonics apply to a free-end medium, such as a fitted rifle barrel?

Does fluting lessen density, in the context of barrel wave patterns?

If so, are there two boundaries and three separately located wave patterns in a fluted barrel; chamber to fluting (dense), fluting (less dense), fluting to muzzle (dense)?

Regards,
John Tracey.
1.6.18

Tim N
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Location: Branxton NSW

Re: Barrel Behaviour Theory

#11 Postby Tim N » Fri Jun 01, 2018 5:43 pm

This stuff is giving me a headache. #-o
We don't rise to the level of our expectations, we fall to the level of our training. Archilochos 680-645 BC

Bigtravoz
Posts: 109
Joined: Sat Apr 22, 2017 7:43 pm

Re: Barrel Behaviour Theory

#12 Postby Bigtravoz » Fri Jun 01, 2018 6:14 pm

So are we inferring that a barrel only waves up and down when a bullet is fired through it? If this is the case you need to re evaluate your thoughts. Calling what a barrel does a wave is incorrect it is closer to a three dimensional oscillation, that also envolves a torsional twist effect. The oscillating effect increases from moment of ignition to a point well after the projectile has left the barrel and then decreases to stationery. This can be somewhat related to how a tuning fork works and in school when I was a kid they showed how the vibrations are not unidirectional. There are a number of factors and variables envolved and has been proven many times mathematical theory relative to it is just that, theory! No two barrels react exactly the same, similar yes but never exactly the same. So we ask why do they differ? One reason is that no two steel bars are ever constituted exactly the same, tooling wears from one barrel to the next, thickness and profile of the barrels changes from one to the next, a chamber on one barrel will always be slightly aligned differently from one barrel to the next and a myriad of other influences between when the bar of steel is made and a bullet travels through it. Hell I have even seen steel bars that measured exactly the correct dimensions every way they were measured but when dialed they were trilobal by 0.05 of a mm, doesn’t sound much until you try to fit it into a precision ground bearing. So in the end you can theorise about it all you like, but the reality is that when you put a series of holes in a piece of paper at 600-1000 yards yo will see what it does far better than any mathematical equations can tell you.

Gyro
Posts: 349
Joined: Sat Jun 10, 2017 2:44 pm
Location: New Zealand

Re: Barrel Behaviour Theory

#13 Postby Gyro » Fri Jun 01, 2018 7:11 pm

True Big T, the theory is absolutely NOT totally sound to me either, and I'm sure many others, but Peter has given us a sort of a "conceptual framework" to work with here so maybe we can go forward with some useful discussion.

Remember that there are 'places' in the big picture where the rifles accuracy hits a sweet spot ............. so there is something going on ???

Bigtravoz
Posts: 109
Joined: Sat Apr 22, 2017 7:43 pm

Re: Barrel Behaviour Theory

#14 Postby Bigtravoz » Fri Jun 01, 2018 7:45 pm

Agreed gyro and if you want to understand it better one of the easiest ways to understand how your particular barrel reacts is to load three loads of each particular load in 0.2 grain increments from listed minimum to maximum loads. Fire each at point the same point of aim as best you possibly can on a still day and see what it will do. You will see that some group tighter than others but few of the incremental loads will impact at the exact same point as the other groups. This will be visible at ranges as short as 30 meters but is more pronounced at longer ranges. You will see that they vary not only vertically but horizontally at the same time and it is not uncommon for a lower velocity load to impact higher on target than a hotter load. The trick is knowing where that given load is going to be impacting, and this is what you need to adjust your zero point to. The same thing will happen again when you adjust seating depth. There are two things that need to be approached in our quest for accuracy first is a load of acceptable accurate velocity and pressure and then adjustments to seating depth to obtain consistent point of impact.

Bigtravoz
Posts: 109
Joined: Sat Apr 22, 2017 7:43 pm

Re: Barrel Behaviour Theory

#15 Postby Bigtravoz » Fri Jun 01, 2018 8:19 pm

One thing that needs to be considered also is that there is not just one wave moving in one direction but thousands of small oscillations moving outward in every conceivable direction both toward the muzzle and returning from the muzzle in a radial fashion outward from the bore and each of these oscillations has an effect on the ones that they encounter. Some will be dominant and larger than others but even the recessive ones will have an effect over the larger ones. You also have twist imparted at different amounts as the projectiles force against the rifling with different amounts of force with different loads and different shoulders holding against both the recoil and twist of the rifle in recoil. Some rifles are just dogs to get to shoot well but others are easy and in my limited experience I have found that once I have found the correct seating depth (ogive placement) for a barrel it is then just a matter of finding the correct pressure load for a given projectile, for instance in my 243 I run both 85 grain Sierra game king hollow point boat tails and 70 grain nosler varmageddons, most accurate load is with the exact same ogive length, point of impact is very similar vertically at 100 meters however one requires more windage to impact the same point. This displays the point that the effect is more oscillating than waving. In reality to appreciate exactly what is happening in a barrel we would need to load a single unchanging case with exactly the same load repeatedly, measure each round for velocity extremely accurately and have a number of hertz readings taken and recorded of the vibration through the barrel that records from start to finish of vibratory cycle.


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