Vertical Dispersion: Flat spots on the MV ladder test are meaningless

[CharlieNC]

This is is the kind of candor that sets up advancement of the ball. It is very hard to distill explanations with a thick tube of steel and velocity in the way of visual observations.

We do know that bullets follow natural laws as they are just faster thrown rocks, at the end of the day. (I’m not being glib, generalizing just from a couple different 700’s in the closet, I’m mainly Fclass but I build up and shoot match guns from .22 to BMG, for myself, with backyard shooting ability exceeding ELR match distance.)

While we don’t know all the whys, tuning explanations that don’t follow the reality of physics, cannot be the reason behind the veil. If I were to cut the end of the nose off a bullet, and I have done this, it would be lighter, and leave the muzzle faster. It would have a lower BC, and yes, that means it would converge at some distance with a perfect bullet. (When I did this, and more, I really restrained myself from saying a thing or two about 100 yard BR).

But identical bullets, shot at different velocities, diverge immediately, and continuously, from the barrel onward. I’m not saying it’s a lot, just that it’s true. It would be hard for guys here to agree on much, if they don’t agree with this precept.

But those identical bullets leaving at different velocities also exit the barrel at a different barrel time, and therefore different point in the barrel's vibration cycle. And when properly timed the vertical poi is the same due to positive compensation, unless you don't believe in that.

 

[6bra1k]

the guys trying to have a discussion about 1000 yard load development seem to have missed that the writer does not own a rifle that fits in the category. he used data from another shooter with a elr possible gun but not a br gun. lots of wasted storage in the clouds. i too will see some of you on friday for an actually 1000 yards shoot vs a discussion of what does not work

 

[davidjoe]

But those identical bullets leaving at different velocities also exit the barrel at a different barrel time, and therefore different point in the barrel's vibration cycle. And when properly timed the vertical poi is the same due to positive compensation, unless you don't believe in that.

I’m brand new to the term as of Keith’s last video. All I know of PC is that Keith says no at long range, a top .22 guy said no, meaning short range, and some years back, Alex Wheeler and many said yes, it’s the way that groups are smaller than SD/ES suggest. I had searched a thread here.

 

[gunsandgunsmithing]

But those identical bullets leaving at different velocities also exit the barrel at a different barrel time, and therefore different point in the barrel's vibration cycle. And when properly timed the vertical poi is the same due to positive compensation, unless you don't believe in that.

This is mostly true and is a good point. But you can have different muzzle velocities while having identical "in bore times", due to pressure curves, ie, how it builds pressure relatively.

IME, particularly speaking to mid to long range shooting, I want very low extreme spreads. It is true that the tightest es might not give the best overall tune but tuners fix that...again, that is my experience. ES dictates external ballistics and a tuner simply times bullet exit with placing the muzzle where accuracy is best, ideally, with very low ES. A good rifle and load that gives low es can always(IME) be tuned to shoot small...with the tuner. Tuners aren't theory any more. PC is a different story but I do believe it is real and I have plenty of reason for believing this. The problem is proving it. I think to get the most of PC, we'd be shooting something that looks drastically different than what our rifles look like today. I'm not sure that 100% of PC is attainable period but that whatever we can attain is a good thing and that lower ES makes that less beneficial.

 

[X Count]

Both arguments are rite in some way and it seems to mostly depend on the BC and velocity of the bullet and where it starts really dropping off in trajectory. Like a lot of high BC bullets say 80gr 224, 185gr 308, 180gr 7mm will hold very pretty well out to 7-800yds with average ES. Say in the 25fps range. You can have a barrel that is in great barrel tune and because the trajectory is still relatively flat the ES isn't yet the dominating factor. Take it out another 300yds and your in trouble but stay within the realms of the BC and velocity and the barrel tune will get you a good score. So not really surprised that old mates gun shot well with poor ES at 600yds because it probably had a good barrel tune.


I do repetitive velocity ladders and shoot paper at the same time and then overlay the results. Many barrels the velocity node at least partially overlaps the barrel node but if those things don't over lap you really need a barrel tuner to make them comply or at least choose a node that there is a fair compromise. ie Maybe the lower fps node overlaps with the barrel node but the upper fps node looks flatter but is offset from the barrel node so leave it alone.

 

[INTJ]

This is mostly true and is a good point. But you can have different muzzle velocities while having identical "in bore times", due to pressure curves, ie, how it builds pressure relatively.

IME, particularly speaking to mid to long range shooting, I want very low extreme spreads. It is true that the tightest es might not give the best overall tune but tuners fix that...again, that is my experience. ES dictates external ballistics and a tuner simply times bullet exit with placing the muzzle where accuracy is best, ideally, with very low ES. A good rifle and load that gives low es can always(IME) be tuned to shoot small...with the tuner. Tuners aren't theory any more. PC is a different story but I do believe it is real and I have plenty of reason for believing this. The problem is proving it. I think to get the most of PC, we'd be shooting something that looks drastically different than what our rifles look like today. I'm not sure that 100% of PC is attainable period but that whatever we can attain is a good thing and that lower ES makes that less beneficial.

Guys have differing ideas on positive compensation. If by PC we mean that a gun that shoots a 3/4" group at 100 yds will shoot a 1/2" group at 300, then Bryan Litz disproved that with his shoot through targets.

Now if we say PC is when a slightly higher powder charge will impact lower than a slightly lower powder charge, then we see that all the time during BR tuning at 1000 yds.

 

[tom]

the guys trying to have a discussion about 1000 yard load development seem to have missed that the writer does not own a rifle that fits in the category. he used data from another shooter with a elr possible gun but not a br gun. lots of wasted storage in the clouds. i too will see some of you on friday for an actually 1000 yards shoot vs a discussion of what does not work

I test hunting guns the same way, and see the same things. It just takes longer, and of course they don't shoot as precise as often. Honestly, as I said earlier I skipped some stuff in the thread. I guess I was unsure what @Beiruty was actually saying originally. And I thought it to be rather rude some of the posts I did catch directed to him. Did he actually piss in someone's Wheaties somewhere, and I missed it? Anyway, good luck and safe travels....I'll be out scouting for moose!

@davidjoe have you ever seen a sine wave target out of one of the short range tards like Bart? Or these powder group/ladders me or another long range benchrest guy's has posted? Do you believe in "nodes", and that a rifle comes into and out of tune? If so, what would you suggest causes that?

Tom

 

[Tarmacshooter]

Guys have differing ideas on positive compensation. If by PC we mean that a gun that shoots a 3/4" group at 100 yds will shoot a 1/2" group at 300, then Bryan Litz disproved that with his shoot through targets.

Now if we say PC is when a slightly higher powder charge will impact lower than a slightly lower powder charge, then we see that all the time during BR tuning at 1000 yds.

Do you have a link to the Litz article or video?

 

[davidjoe]

@davidjoe have you ever seen a sine wave target out of one of the short range tards like Bart? Or these powder group/ladders me or another long range benchrest guy's has posted? Do you believe in "nodes", and that a rifle comes into and out of tune? If so, what would you suggest causes that?

Tom

Yes, I have seen them. My understanding of that effect has been that the barrel is vibrating, starting upon trigger pull, and the muzzle is pointing in very slightly different directions when the bullet is released. Those sine wave tests I’ve seen are premised on different charge weights causing the bullet to be released at different velocities, but more importantly, at different points in the muzzle’s movement. Having a large ES when a single load has already been chosen, would seem to me to unpredictably cause that dispersive effect.

 

[gunsandgunsmithing]

Guys have differing ideas on positive compensation. If by PC we mean that a gun that shoots a 3/4" group at 100 yds will shoot a 1/2" group at 300, then Bryan Litz disproved that with his shoot through targets.

Now if we say PC is when a slightly higher powder charge will impact lower than a slightly lower powder charge, then we see that all the time during BR tuning at 1000 yds.

I don't think I've got a 3/4" rifle, so that's not what I'm referring to at all. I'm strictly talking BR stuff.

Litz is on the right track and I mostly agree with him. In it's most basic form, PC is about slightly different velocities impacting at the same point due to different launch angles and exit timing. How much can be compensated for is debatable and I alluded to that when I mentioned a rifle looking very different than what we typically shoot, if trying to get as much PC as possible is the goal, and there will be compromises. There's a lot more to it than you mention...mostly center o gravity and rotation of the gun..in all planes. Frankly, most all of us would be better served worrying more about wind calls and not pulling the trigger at the wrong time...but there is something to PC, over and above simply having low ES numbers. Besides what I've seen, there's a good bit of evidence that supports it being real. The problem comes when someone claims it's false because you can't or maybe haven't achieved 100% velocity compensation and can't claim it to completely negate ES. It does not completely negate it and how much is very gun design dependent. It's very much a subject worth its own thread but I won't likely be a big player in such a thread because, as you can probably see from this post, it can be controversial and people that have actually tested it in any scientific form or one resembling it, are likely counted on a few fingers.
My vibration analysis testing wasn't geared in that direction but we did come across a couple of things that give it scientific credence, IMHO. Just not enough for me to claim much as factual. I'll say this..there are a lot of variables but I think most will agree that we see some PC happening in existing builds, with and without tuners, but there's more to be had. IMO, a lot more, but even if 100% velocity compensation for say..20fps were the goal, well...that seems feasible to me...and maybe a bit more than that.

 

[tom]

I've lost a lot of pictures from a phone mishap about a year and a half ago, but here's some examples of what I'm seeing.



Above fired at my power line 871 yard spot.





Again my power line spot.

This one at deep creek 1,000 back in March this year.

Not ridiculous ES, but often times 20ish will have less vertical.

Tom

 

[gunsandgunsmithing]

Yes, I have seen them. My understanding of that effect has been that the barrel is vibrating, starting upon trigger pull, and the muzzle is pointing in very slightly different directions when the bullet is released. Those sine wave tests I’ve seen are premised on different charge weights causing the bullet to be released at different velocities, but more importantly, at different points in the muzzle’s movement. Having a large ES when a single load has already been chosen, would seem to me to unpredictably cause that dispersive effect.

I'm not davidjoe but of course I have seen it with and without tuners.. plainly and clearly, as long as the gun and load are decent. And yes, I agree with you about velocities and dispersion. My tuner test that I have everyone do now, is all about that very thing because the key to using tuners effectively is recognizing group shapes and relating that shapes to how far out of tune you are. The same can and has been done both with and without tuners. The test is about 3 things and is a "light bulb moment
". It shows how far it is from completely tuned to completely out of tune, which quantifies frequency on target.. typically only about 4-5 marks ON MY TUNER. It shows top and bottom of the bbl swing(aka sine wave) and it shows group shape at respective settings from all the way in tune to all the way out of tune, again, 4 or 5 marks is absolutely remarkably predictable.
Top or bottom of the sine wave, or bbl swing, is relative here due to positive compensation. As I see it, PC can only occur at the TOP of the bbl swing. That's why I go to the trouble of establishing top and bottom on target fwiw. That said, It's common for a single 3 shot group at 100 yards be smaller at the bottom than at the top, but statistically, it's 50/50, which makes sense.

 

[INTJ]

Do you have a link to the Litz article or video?

It was in one of his ballistics books. Modern Advancements in Long Range Shooting Vol 2, Chapter 2.

 

[David Christian]

I just wasted 30 minutes of my life trying to see if this thread was going anywhere…I will never get that time back.

 

[Beiruty]

I just wasted 30 minutes of my life trying to see if this thread was going anywhere…I will never get that time back.

Someone like Bryan Litz spend their life to be better at internal and external ballistics.
I recommend you buy his new book coming out in September

 

[Dave M.]

Dave,

I am an engineer, an experienced reloader, steel target shooter from 500 yards to 1270 yards, the longest at our club. I shot a couple of times at 2200 yards range.
My rifles could be anything from AR to 30" heavy barrel 300WM rifle.
My passion is to learn more and more about internal and external ballistics for small arms.

I do not compete for trophies.

You should definitely compete for trophies and see how your theory holds up long term against the others greats in the game.

 

[Dave M.]

Someone like Bryan Litz spend their life to be better at internal and external ballistics.
I recommend you buy his new book coming out in September

You realize there are dozens of shooters on this forum that likely know Bryan on a first name basis. Some true legends lurking on this forum, I’ve learned this first hand

 

[Beiruty]

You should definitely compete for trophies and see how your theory holds up long term against the others greats in the game.

I agree.

 

[johnfred1965]

You realize there are dozens of shooters on this forum that likely know Bryan on a first name basis. Some true legends lurking on this forum, I’ve learned this first hand

I hope that one horse's a$$ that has been posting on here is a legend. I'd hate to think I read all that BS from a regular shooter like me.

 

[Tarmacshooter]

I hope that one horse's a$$ that has been posting on here is a legend. I'd hate to think I read all that BS from a regular shooter like me.

Who is the horses ass?