Does Positive Compensation exist @ 600yrds?

[308win]

in my mind it shouldn't matter, if you've found positive compensation/ convergence they should converge at every distance.

I have to disagree (in theory, no experience). You are tuning the slower bullet around the faster bullet. In order to have the same POI at a given distance the slower bullet has to fly on a higher trajectory. They can only converge at one point down range and so forth have to be tuned to do that. If you move closer, the slower bullet will start impacting higher and higher as you move the target closer or lower as the target gets further away from the original POI range. This is why I have given up on the method as far as hunting setups go. Stick with the tried and true Ladders at distance.

 

[bluedog69]

I have to disagree (in theory, no experience). You are tuning the slower bullet around the faster bullet. In order to have the same POI at a given distance the slower bullet has to fly on a higher trajectory. They can only converge at one point down range and so forth have to be tuned to do that. If you move closer, the slower bullet will start impacting higher and higher as you move the target closer or lower as the target gets further away from the original POI range. This is why I have given up on the method as far as hunting setups go. Stick with the tried and true Ladders at distance.

I am brand new at this theory, so my opinion may be dead wrong. I am kind of seeing this the same way you are. What happens at 60 yards? What about 40?
I can see where this could be huge for competition in 22 LR. You can't run a bunch of powder and seating depth tests to tune with. So tuning the fast and slow to be crossing at the same time at a given yardage would be huge as shown by their groups.
In center fire we are trying to elimate the fast and slow until they are all the same speed.

 

[Taylorbok]

I have to disagree (in theory, no experience). You are tuning the slower bullet around the faster bullet. In order to have the same POI at a given distance the slower bullet has to fly on a higher trajectory. They can only converge at one point down range and so forth have to be tuned to do that. If you move closer, the slower bullet will start impacting higher and higher as you move the target closer or lower as the target gets further away from the original POI range. This is why I have given up on the method as far as hunting setups go. Stick with the tried and true Ladders at distance.

I ran some numbers and ya your theory seems to math out.
I thought you'd see the vertical due to velocity reduced at all distances but if you come back to like 2/3 where your convergence is you basically get the "correction" doubling what the vertical would be so it would essentially put the bullet roughly the same out the top.

Turns out its pointless unless you are shooting at one distance.

 

[nealm66]

I have to disagree (in theory, no experience). You are tuning the slower bullet around the faster bullet. In order to have the same POI at a given distance the slower bullet has to fly on a higher trajectory. They can only converge at one point down range and so forth have to be tuned to do that. If you move closer, the slower bullet will start impacting higher and higher as you move the target closer or lower as the target gets further away from the original POI range. This is why I have given up on the method as far as hunting setups go. Stick with the tried and true Ladders at distance.

This is how I understand it as well. From the hunting perspective, let's say you tune at 1000 and end up inside 10". Then falls out of tune and is again 10" at 600, 5" at 300, you get the jest. I've never tried it but I believe it works. I've used a tuner since the mid 90's on every rifle I've owned. I should tune at 600 for competition but I'm lazy and 200 gets me usually in the top 3

 

[nealm66]

@308win , you should try a tune with a good hammer bullet. They're expensive but they shoot very good to distance and will be very good for your experiment

 

[Doom2]

FWIW, as to the original question, for a 308 169 SMK traveling at 2700 fps to have positive compensation for -20fps at 600 yds it would take a barrel deflection of~+0.00036" (assuming a 26" Barrel) to have the same impact point. This is based on a point of impact variance for the 20 fps of 0.3 MOA.

There is a paper where a group in China measured the deflection on a sniper rifle at +/-.99 mm. which is about 0.039". Based on that deflection it is plausible that positive compensation could be utilized but it would require detailed analysis of the first portion of the vibration with bullet travel time to determine whether it could be utilized.

Study on barrel vibration characteristics of typical sniper rifle - Extrica

The firing accuracy of sniper rifle is significantly affected by the barrel vibration induced by shooting load. The barrel vibration is an important parameter needing to be precisely controlled, whose measurement is less studied before. The vertical vibration characteristics of sniper rifle...

www.extrica.com

Testing and proving that positive compensation actually could be utilized would be difficult considering the amount of noise that would be present due to the number of variables involved. Triying to "tune" to a particular distance would be extremely difficult due to the number of rounds required to achieve repeatable results.

I saw a video where Scott Satterlee worked on seating depth at 100yds and used his Chronograph to pick a seating depth where his POI on with the slower round was above the faster rounds. Does it help? I don't know but the concept probably makes sense and has no apparent downside.

 

[Beluebow]

Turns out its pointless unless you are shooting at one distance.

Doesn't make it pointless....gun will shoot amazingly well at all yardages.

 

[RockyMtnMT]

My take on this is it would be a great method for people to use when tuning loads with our bullets. I think it would boost sales. A great game to play for the guy with full on tinkeritus.

 

[nealm66]

I wouldn't be too surprised if there were more than a few that tune your bullets at distance. Not really going to create a huge jump in sales I wouldn't think. I've seen a few times where guys are coloring their bullets and shooting groups at distance at my range. I took a big tree down ( I do logging and tree removal) for one of them and was interesting to hear his take on it as he was using the process for creating a hunting load. Looked like jibberish on paper to me but he was as quite pleased with the results

 

[RockyMtnMT]

It was supposed to be a joke. I'm very much not a tinkerer. My goal is half moa done in less than 20 shots.

 

[nealm66]

Shhh, you're going to upset the Hornady guys

 

[Alex Wheeler]

I first became interested in PC about 15 years ago. At that time I thought I had came up with some original idea just based on what I was seeing. When I looked into it I saw that it was a very old concept. Ever since I have yet to see anything to make me think it does not work if you tune for it. In fact I base all my personal shooting success on it. Most successful LR BR shooters and F Class shooters are tuning for it, whether they know it or not.

 

[Alex Wheeler]

Its much harder to see in close. 600 in is kind of close but its still there if your shooting small enough.