Node !!

[Todd Earhart]

The barrel is a noodle. More so than many realize. When the pointy end is pointing at the same location as the bullets exit, the groups are small. When it is not... well... we've all been there.

Fact

 

[big5ifty]

So, then there is no way that any barrel/internal ballistic phenomenon would make a higher velocity bullet group with a lower velocity bullet.

Apologies, I missed responding to this at the time.

There is, and it does.

Higher velocity bullets group with lower velocity bullets, and OCW proves that it can and does occur within a 3% charge range.

Anyone can prove OCW for themselves in their rifle.

The reasons for it are not clearly understood, there is a lot of theory being thrown around as to why it occurs.

 

[praveen]

Apologies, I missed responding to this at the time.

There is, and it does.

Higher velocity bullets group with lower velocity bullets, and OCW proves that it can and does occur within a 3% charge range.

Anyone can prove OCW for themselves in their rifle.

The reasons for it are not clearly understood, there is a lot of theory being thrown around as to why it occurs.

You’re using OCW to prove that OCW works? Thats circular logic.

 

[big5ifty]

You’re using OCW to prove that OCW works? Thats circular logic.

Possibly, but to disprove something is the same a proving it in that either way you have to do it.

Because the effect is not defined quantitatively, it's not possible to prove or disprove otherwise.

 

[CharlieNC]

Possibly, but to disprove something is the same a proving it in that either way you have to do it.

Because the effect is not defined quantitatively, it's not possible to prove or disprove otherwise.

Positive compensation has been proven, going back several years.

 

[gunsandgunsmithing]

Positive compensation has been proven, going back several years.

Yes. The question becomes, how do we get as much of it(pc) as possible. I think you'll agree that stock and overall design of what we currently shoot may not be the most conducive design for this one aspect of making these things shoot. That's one reason I don't hang my hat on pc and look more at accuracy and groups that are easy to read when tune goes away vs focusing hard on pc. If I can see tune on target, I feel like I can fix it. It's those guns/groups that shoot pretty good, just not good enough, even when a little out of tune that drive me crazy. I call it "talking to me." I actually prefer it to shoot big but still predictable shapes when it starts going out of tune on me because I move my tuner based on group shape above anything else. POI is relative to pc but I put that secondary to group readability. Maybe further down the list of things that matter to me when tuning.

 

[CharlieNC]

Yes. The question becomes, how do we get as much of it(pc) as possible. I think you'll agree that stock and overall design of what we currently shoot may not be the most conducive design for this one aspect of making these things shoot. That's one reason I don't hang my hat on pc and look more at accuracy and groups that are easy to read when tune goes away vs focusing hard on pc. If I can see tune on target, I feel like I can fix it. It's those guns/groups that shoot pretty good, just not good enough, even when a little out of tune that drive me crazy. I call it "talking to me." I actually prefer it to shoot big but still predictable shapes when it starts going out of tune on me because I move my tuner based on group shape above anything else. POI is relative to pc but I put that secondary to group readability. Maybe further down the list of things that matter to me when tuning.

Accuracy certainly requires several elements which are optimal, and in harmony with each other. PC is just one which is tunable, and probably holds more potential pending in depth study.

 

[gunsandgunsmithing]

Accuracy certainly requires several elements which are optimal, and in harmony with each other. PC is just one which is tunable, and probably holds more potential pending in depth study.

That was my point too. I think a gun designed specifically for getting as much pc as possible would look a lot different than what we typically shoot. What we shoot works pretty well for strictly accuracy and feasibility, not to mention meeting the various rule books. But I think testing more for pc will yield some useable info and you're right...it hasn't been thoroughly tested, that I'm aware of. A guy by the name of Keith Sharpe did some testing a few years back. Sharp guy, a professor at the University of Louisville..mechanical engineer, I think. I remember the gun he was shooting was built very much for pc with a lot of attention to its center of gravity and how it rotates around it in all directions..fwiw. Fugly ass gun though! Lol!

 

[gunsandgunsmithing]

He did win his share of matches

 

[Alex Wheeler]

I am a big pc guy so far as I have tried to exploit it as much as possible with gun design. I dont have any hard facts I can prove but I have a lot of observations. In my opinion the main thing that dictates pc is the powder. The powder sets up the pressure curve which sets up the harmonic. Yes you can do things with stocks and c/g and see that on target but its small compared to a powder change. You can literally make a gun go from pc to nc with a powder change. Its all about those barrel harmonics.

 

[gunsandgunsmithing]

Powder charge can only affect amplitude but I don't doubt that you're seeing something that is likely not vibration related but that can very much affect tune windows. So we might be saying the same thing or not. Along those lines, I've always said that tuners don't "create" pc but they might make it more clear and allow us to manipulate bbl position to time up with bullet exit, that allows for pc to be more usable to tune with. Again though, more testing should be done to better understand it and how we can make it of more value to us.

 

[Alex Wheeler]

I didnt mean powder charge, I meant switching powders. The effect different powders have on the harmonic and pc is by far larger than any other variable I have seen to date. In my opinion tuners hurt pc at long range as a general statement. But theres more than one kind of pc.

 

[BP1]

I didnt mean powder charge, I meant switching powders. The effect different powders have on the harmonic and pc is by far larger than any other variable I have seen to date. In my opinion tuners hurt pc at long range as a general statement. But theres more than one kind of pc.

So you would leave a tuner off a barrel on a 1000yd rifle and just try different powders and see what shoots best? Just trying to understand.. thanks

 

[gunsandgunsmithing]

I didnt mean powder charge, I meant switching powders. The effect different powders have on the harmonic and pc is by far larger than any other variable I have seen to date. In my opinion tuners hurt pc at long range as a general statement. But theres more than one kind of pc.

Different powder and/or different charge, the same still applies. I can understand why you might think tuners hurt pc but IME, the opposite is true. The big thing I think to remember here is that while more weight at the end of the beam(bbl) will typically reduce amplitude,(physics teaches us that this is true) , it does so over time. The time we are worried about though, is while the bullet is still in the bbl, which of course is a very short period.
In reality though, during that short period we are worried about, amplitude is actually increased rather than decreased. The bbl is already under tension and drooping downward before the trigger breaks. Now is when stuff starts moving. But physics also teaches us about the equal and opposite energy aspect, in this regard to bbl movement during that very short period of time. The bbl is already deflecting before the gun goes off and it responds in kind when excited by the explosion and the bullet beginning its travel toward the muzzle, Yes, one would assume same as you but I promise that I'm not knowingly gonna disagree with physics without good reason. That reason is vibration analysis and seeing it physically happen on the o-scope. Not looking to argue at all, but I hope this will help anyone understand what's going on better is all. Assuming less amplitude is getting off to a bad start. And yes, it's very understandable that one would assume that amplitude would be reduced. The key is time.

 

[Alex Wheeler]

So you would leave a tuner off a barrel on a 1000yd rifle and just try different powders and see what shoots best? Just trying to understand.. thanks

No thats not what Im saying at all. And I should not have said tuners, I should have said any device that ads mass to the muzzle. One component of building pc into a rifle is the fact the rifle wants to rotate on it c/g while the bullet is traveling down the barrel. We need that for pc. So adding weight to the ends of the rifle is not something you would do to encourage that. We need to get the muzzle traveling up. Thats why a softer stock helps, its like a spring with stored energy. But there are much larger driving forces on the harmonics, so you can still get there with a muzzle device. Its not all about getting as much pc as possible, you only need the right amount. The other thing you see when you add a muzzle device is the poi becomes more stable. We need poi change to get pc at longer ranges. But theres still enough to make it work as many guys are doing it. If you could imagine an extreme example of no barrel harmonics and a tune going through the same hole at 100yds, your down range groups could not shoot less vertical than the es predicted.

 

[M-61]

You will go crazy trying to understand why it happens

Yes. I’m crazy enough. This I choose for mental health reasons to take a full pass.
I like looking at my groups. ( most times)

 

[Skedaddle Shooter]

All this talk about nodes, it is a mystical thing

 

[CharlieNC]

No thats not what Im saying at all. And I should not have said tuners, I should have said any device that ads mass to the muzzle. One component of building pc into a rifle is the fact the rifle wants to rotate on it c/g while the bullet is traveling down the barrel. We need that for pc. So adding weight to the ends of the rifle is not something you would do to encourage that. We need to get the muzzle traveling up. Thats why a softer stock helps, its like a spring with stored energy. But there are much larger driving forces on the harmonics, so you can still get there with a muzzle device. Its not all about getting as much pc as possible, you only need the right amount. The other thing you see when you add a muzzle device is the poi becomes more stable. We need poi change to get pc at longer ranges. But theres still enough to make it work as many guys are doing it. If you could imagine an extreme example of no barrel harmonics and a tune going through the same hole at 100yds, your down range groups could not shoot less vertical than the es predicted.

Yes that is exactly what can be determined from a ladder target to break out the ballistic slope vs the harmonic slope. What's missing is the knowledge of how to manipulate the harmonic slope to get the ideal offset which you describe. I'm happy to carry out that analysis if someone(s) can generate the data (barrel contours, stocks, etc).

 

[Todd Earhart]

Yes that is exactly what can be determined from a ladder target to break out the ballistic slope vs the harmonic slope. What's missing is the knowledge of how to manipulate the harmonic slope to get the ideal offset which you describe. I'm happy to carry out that analysis if someone(s) can generate the data (barrel contours, stocks, etc).

Barrel contour important.
Todd

 

[jimmymac]

Someone in this thread asked about mixed powder charge groups and if they would print to the same POI. Here is one I did recently during some load work up with a PPC. I had 5 loaded rounds left. Three at one powder charge and two at half grain difference in powder charge. Both shot to the same POI as I suspected because I tested it. On that particular day both loads were shooting well. The day prior, the hotter load would not shoot with the milder load. This is why I test. It’s also why I test during matches because what worked yesterday or this morning may not work this afternoon. I’m clueless how you long range guys keep your guns in tune. At short range I’m frequently fussing with powder to try and stay on top of it.