Ladder Test Diagnostics

[LRVarminter]

I shot a Ladder test at 100yd yesterday with my 6.5X47. I was expecting to see vertical stringing as velocities increased until a maximum charge was exceeded, this should have gone high and right. Instead I got a gradual climb in shot placement with velocity until the 7th shot went to the left. After that all shots went left as seen in the picture.


Can anyone can tell me what causes this rather than a continual vertical stringing?


Load data;
Case: Lapua, neck turned .003"
Primer: CCI 450 small rifle magnum
Powder: AR2213SC. Starting at 38.2gr and increasing to 42.2gr in 0.3gr lots
Projectile: Berger 140gr Match VLD.

Barrel: Shilen SS, 26'',1 in 8'' twist.

Please excuse picture rotation, I tried and failed to fix it. Target was shot with 'S3' vertical.

[SCJ429]

Was there a wind shift? Barrel harmonics.? Did you record the velocity of these shots? If so, do your testing around the fastest ones that have similar velocities.

[LRVarminter]

There was no wind to speak of on the day, nothing touched the barrel during the 100yd group. Shot a 5 shot group at 200yd with charges around the middle of the ladder test where they started shifting left, I had a magneto speed attached for this and had exactly the same results.

40.4gr - 2544fps
40.7gr - 2562fps
41.0gr - 2585fps
41.3gr - 2605fps
41.6gr - 2622fps

Shots 1,2 and 3 strung downward in the 8 O'clock direction (interesting in its self) all touching. Shot 4 is 10mm high and about 2mm left from shot 3. Shot 5 is 13mm left of shot 4.

Please excuse the detailed description. I tried to upload another picture...

[marksman]

if you take the target out to 300 you will see more differences on the target with a shooter
and that is why you are seeing a gradual climb in shot placement
the rifle is a shooter
pick a powder weight that is stable and do a seating depth test at 300

[LRVarminter]

Thanks Marksman. I'm confident that after seeing similar results at 100 and 200yd. that the results could be extrapolated at 300m. But hey, any excuse to get behind the trigger is good enough for me

What I am most interested to find out is why the rounds point of impact move to the left with an increase in velocity either due to an internal and external ballistic phenomenon; or my shooting, say my trigger manipulation for example? I expect I'll have no problem getting the rifle to shoot well at this point, I'm just hungry for information

[marksman]

this is just a theory but
maybe it is because the barrel is indexed so the barrel harmonics release the bullet to the side instead of up
I know when I get a re-barrel I always get them indexed to 12 oclock part of being consistent and truing everything

[LRVarminter]

I did a bit of research, I think you could be on the money there. Thanks. I'll put a few more rounds down it and then ask the gunsmith if it begins to cause me problems

[Kelsey Cooter]

this is just a theory but
maybe it is because the barrel is indexed so the barrel harmonics release the bullet to the side instead of up
I know when I get a re-barrel I always get them indexed to 12 oclock part of being consistent and truing everything

Could you explain what indexing is please marksman?

[straightshooter]

It never ceases to amaze me just how much many shooters love to believe in magic rather than the simplest explanations for various shooting phenomena.
A so called ladder test may have some degree of validity if the receiver were secured in a rigid immovable mechanical rest and the firearm ammunition combination were capable of good reliable accuracy and the test is done at sufficient range so there can be a measurable effect on the trajectory of the projectiles. Otherwise it is subject to all the usual variables encountered in shooting, many of which will overwhelm the quantity you are attempting to measure.
So what are these variables that may be a source of error?
Besides the accuracy of your ammunition the include:
Variations in parallax when using the scope.
Variations in hold on the rifle.
Variations in recoil path of the rifle.

[marksman]

this is just a theory but
maybe it is because the barrel is indexed so the barrel harmonics release the bullet to the side instead of up
I know when I get a re-barrel I always get them indexed to 12 oclock part of being consistent and truing everything

Could you explain what indexing is please marksman?

sorry for not seeing this Kelsey but I have been away hunting
basically it is finding the natural curve of a barrels bore and setting that at 12 or 6 o'clock when the barrel is fitted so there is no tendency for a barrel to want to vibrate any other way than vertical when fired. This means the shooter tunes the vertical out as per normal and a high level of accuracy is achieved.

[Kelsey Cooter]

sorry for not seeing this Kelsey but I have been away hunting
basically it is finding the natural curve of a barrels bore and setting that at 12 or 6 o'clock when the barrel is fitted so there is no tendency for a barrel to want to vibrate any other way than vertical when fired. This means the shooter tunes the vertical out as per normal and a high level of accuracy is achieved.

I find that really interesting marksman, i have a 223 that seems to react to every different distance, projectile or powder, by shooting further or not so far to the right. Really noticeable if its next to another 223. It groups around half moa, but as the distance increases it sends them alot further right than any other 223

[Homer]

G'Day Fella's,

LRVarminter, thanks for the interesting read.

FYI, when I first got my 6.5x47 Lapua (26", 1 in 8" twist), I was advised the best powder for it, was ADI, AR-2209.
I was told I should be able to safely obtain 2700 fps, with 40.0 grns of 2209, under 140/142 grain bullets.
I have only loaded to 40.0 and achieved 2650ish fps, without any indications of high pressure (with Lapua cases and CCI BR4 primers).

Given this, when I get a chance, I will continue to work up a load, and see if I can safely achieve, 2700 fps with 2209 powder.

Hope that helps

D'oh!
Homer

[marksman]

sorry for not seeing this Kelsey but I have been away hunting
basically it is finding the natural curve of a barrels bore and setting that at 12 or 6 o'clock when the barrel is fitted so there is no tendency for a barrel to want to vibrate any other way than vertical when fired. This means the shooter tunes the vertical out as per normal and a high level of accuracy is achieved.

I find that really interesting marksman, i have a 223 that seems to react to every different distance, projectile or powder, by shooting further or not so far to the right. Really noticeable if its next to another 223. It groups around half moa, but as the distance increases it sends them alot further right than any other 223

I first heard about it from Bill Hambley-Clark who is a dead set gunsmith legend

[TassieTiger]

I’m relatively new to shooting but I’ve done a lot of testing and I don’t think it was mentioned or asked but did you also consider barrel temperature??

I’ve witnessed some rather strange bullet pattens from various rifles once barrels get hot, as the metal expand...this temperature increase has got to change barrel harmonics...and subsequently, has to change point of impact...
I try and only shoot comparative groupings with barrels that are similar in temp but it’s not always possible.