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Ladder testing at 1k- Detailed article and video

 
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  #8  
Old 05-29-2009, 01:15 PM
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Re: Ladder testing at 1k- Detailed article and video

Quote:
Originally Posted by phorwath View Post
I know enough from my experiences to confirm that good chrono nodes in themselves don't guarantee good results on paper. And the POIs are what really matters, when all is said and done. In other words, one could establish a good long range load without a chronograph, but one could not rely on chronograph data alone without the POIs on down range targets to confirm a good load. The chrono data might be helpful, but that's the most it can be - an aid to efficiently ID'ing loads with the potential to deliver quality down-range POIs.

For the most part I agree, however only when you are talking about a single distance. there is no way to have 2 bullets follow the same trajectory from start to finish unless the velocities are nearly the same. Barrel harmonics and differing velocities can cause 2 different bullets to impact the same at some given distance, but it would only be where their trajectories intersected.

AJ
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Old 05-29-2009, 02:46 PM
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Re: Ladder testing at 1k- Detailed article and video

Clarifying, my primary point is low ES and SD don't ensure 1/2 moa or better accuracy out of any rifle. If the gun prints 1 1/2 moa, the low ES and SD may help to ensure the down-range groups are circular rather than strung out vertically at long range, but you may as well be shooting buckshot as a rifle.

So the chrono can assist in ID'ing loads with potential for good long range accuracy and minimum vertical stringing, and it can assist in establishing MVs and down-range velocities for purposes of fine tuning ballistic software programs to get good predicted drops and downrange velocity matches, but the proof in the quality of the load is the POIs on down-range targets. And this can be done without any chronograph at all. Since down-range groups that have minimal vertical stringing have by necessity, also identified a load with low ES and SD. I agree with what I believe is being inferred; low ES and SD are required to prevent excessive down-range vertical stringing.

But I've read a number of accounts where shooters fine-tune their reloads simply by down-range target results. It may take them an extra 20 rounds of ammo, but by the time they're getting 1/2 moa at 1000 yds, that load will surely have low ES and SD.

So to go so far as to say I follow the chrono rather than the POIs is overstating the value of the chrongraph data in the bigger picture. If one were to say I believe and follow the POIs rather than the chrono data, then there's no arguing the merits of that position.

Bottom line, chrono data can help lead to more efficient load development, as well as the fine tuning and tweaking of ballistics software. Which is a big deal in itself. I use two of them set up in series whenever I can. But they aren't the final confirmation of anything other than bullet velocity.

Last edited by phorwath; 05-29-2009 at 03:11 PM.
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Old 01-31-2010, 08:20 AM
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Re: Ladder testing at 1k- Detailed article and video

Some folks who shoot accurately at the longer ranges have known for years that some extruded powders have a narrow charge weight range at some value for many cartridges that produces best accuracy all the way out to the longest ranges. Ball powders have never quite done as well.

But nobody's ever proved that ladder testing determines the charge weight producing best long range accuracy makes the bullet exit the barrel at any given point in its whip cycle. To do that, one needs two accelerometers on the barrel (one at the muzzle and one at the barrel's zero movement node back a ways from the muzzle) connected to equipment to display where the muzzle's bore axis is when the bullet exits. A sensor will also be needed at the muzzle to detect when the bullet clears it also has to be feed to that equipment. Then one can see where in the vertical whip cycle and angle the bullet leaves at.

A given barreled action with a scope has one fundamental frequency it whips at with the largest angular movement at the muzzle's bore axis and it never changes regardless of the load shot in it. That frequency is typically less than 100 cycles per second; one cycle in 1/100th or .010 second.

High powered rifle bullets are gone before the barrel's went through 1/6th of a cycle. It's best for accuracy if all bullets leave on the muzzle axis up swing so faster ones depart at a slightly lower angle than slower ones.

Don't think a barreled action's high frequency sound one hears when they smack it with a hammer is what it whips at. That's caused by pressure waves bouncing back and forth between the ends at about 18,000 fps through the steel. That'll be a couple thousand cycles per second and any muzzle axis direction changes at that frequency are insignificant.
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Old 02-08-2010, 12:24 PM
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Re: Ladder testing at 1k- Detailed article and video

Bart that was an interesting response, could you explain what effect on target you would be watching for to indicate that you are getting close to the node where the bullets are leaving the barrell at the highest point in the whip cycle. Pictures of results of ladder testing would really help. Assuming the Sd is keeping within 20 fps. Thank you. Tony
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Old 02-08-2010, 01:06 PM
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Re: Ladder testing at 1k- Detailed article and video

Tony, I don't want bullets leaving the barrel such that their average barrel time puts them to when the barrel's at it high point in its whip cycle. Doing so means that those a little slower with longer barrel times and lower muzzle velocities will leave when the muzzle axis is on its down swing. The barreled action's fundamental whip frequency never changes but its amount does depending on recoil. The faster ones in this group will leave at a higher muzzle angle than the slower ones. And that's opposite of what's best for long range accuracy.

Bullets with lower muzzle velocity will strike lower on the target. If one wants the slower ones to strike in the middle of the group, they have to leave at a higher muzzle axis angle. Conversely, faster bullets should leave at slightly lower muzzle axis angles. This is the reason why British SMLE's in .303 and .308 Win. shoot so accurate at long range; slower bullets leave later in the barrel's whip cycle so they strike higher; faster ones leave sooner so they strike lower. It all averages out.

The only way to do this is to have all bullets leave on the barrel muzzle axis up swing. And this is what happens most of the time. Bullets are gone before the muzzle axis has gone from straight, then down a bit and finally upwards in its first 3 to 4 milliseconds of its 10 millisecond whip cycle. The bullet takes about 1.5 milliseconds to go from case to muzzle.
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  #13  
Old 02-08-2010, 02:47 PM
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Re: Ladder testing at 1k- Detailed article and video

Thanks for the explanation bart that makes sense.
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  #14  
Old 02-09-2010, 09:24 AM
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Re: Ladder testing at 1k- Detailed article and video

Pretty good article and that is very close to the way I work mine up as well---the biggest difference is I will not even consider a load that will not keep 5 shots within 20 fps or less for my 1k competition rifles. I have 2 tubes right now that are 6 and 8 fps respectively in my 6.5x284's.

50 fps will be tough to win with.
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