Why are my ladder tests backwards (hotter loads hitting lower)?

[josh.rizzo]

So I was ladder testing today for my new Savage 10 (.308WIN) with 210gr Berger VLDs and something weird happened. All of my shots were hitting LOWER as the powder charges went HIGHER. The ladder climbed down and a little to the left to be exact. I can't figure out why this would happen! Any ideas?

MORE INFO (everything I can think of):

I confirmed with a chronograph that my velocities were going up as I progressed, despite the faster shots hitting lower. I tried 3 different powders and all of them acted the same. I zeroed my rifle with Winchester match ammo (168gr SMKs) which clocked at 2800fps. The first shots from the ladder were about 2300fps and hit where I was aiming while the last of the ladder hit about 6MOA low and 2MOA left at just over 2500fps (after that I was getting burn marks around the outside edge of the primers and stopped...no other pressure signs). I was watching my barrel and ammo temp with a IR thermometer and made sure each shot was made at the same temp (within maybe 3 degrees). I loaded a group of the highest load (before pressure signs) and they grouped under .5MOA at the same low/left point from the ladder.

The Rifle is the Savage 10FCP that comes in the HS Precision stock. The barrel is a 24" heavy barrel (Savage factory) and has a 1:10" twist. Rifle was bedded with Acraglas. Action screws were both torqued to 30in/lbs. Scope is the Vortex Viper PST 6-24x50 FFP. Scope rings were lapped and torqued to suggested values. I can confirm that the scope is not loose after shooting. The scope base has a 20MOA angle built in. Using a Harris bipod and a Caldwell rear sandbag. No other modifications/equipment that I can think of...

Sorry for the exhaustive data, but I wanted to get everything out there in case something weird could cause this. I'm an experienced 3 Gun shooter, but new to bolt actions (and new to this forum...Howdy all!). My first theory was that it was just the shooter, but the pattern was too consistent. It could be some weird harmonics, but 6MOA vertically is a bit much for that, I think. I can only guess that is has something to do with being at a weird point in my zero, but I'm just grasping at straws at this point.

Any help is appreciated. Thanks!

 

[josh.rizzo]

How far were you shooting? - If only 100 or 200 yards, that is why.

Donovan

It was at 100 yards. it was a windy day so I didn't want to test loads farther than that. Can you explain to me exactly what was happening at that range...its driving me nuts! Thanks!

 

[brxbrad]

Your barrel is on upside down........Merry Christmas

 

[Bart B.]

Your bullets leaving the fastest get out of the barrel before the slower ones do. The muzzle axis is on the upswing when that happens. At some longer range, they'll be together as the slower ones leaving at a higher angle drop less. That's called "positive compensation." But it's rare that it's seen at 100 yards.

It also can be caused when the faster velocity loads are shot with the rifle's butt pad higher in the shoulder. The muzzle axis will swing less upwards as there's more resistance to the rifle's recoil while the bullet goes down the barrel. More often seen when shooting slung up in prone, but can happen shoulder firing the rifle as it rests atop something on a bench.

 

[2506]

It is called barrel lag time. With the slower velocity the bullet stays in the barrel longer and the barrel has time to rise higher in recoil thus your bullet will strike higher. The faster the bullet the less barrel time and thus the bullet comes out of the barrel quicker and thus will striker lower.

 

[MGYSGT]

Your barrel is on upside down........Merry Christmas

Made me laugh and spit my coffee out. Thanks

 

[sailhertoo]

Your barrel is on upside down........Merry Christmas

HA...HA... I was going to say the same thing!

 

[Hondo]

dmoran
No disrespect intended just puzzlement.
If a bullet has not crossed the line of sight by the time it gets to 100 yds it never will.
From the moment a bullet exits the barrel it starts to drop.
To zero a rifle for 100 yds. the bullet must first cross the line of sight somewhere at about 25 yds. depending on the velocity of the bullet and the distance to the target.

 

[kyreloader]

To zero a rifle for 100 yds. the bullet must first cross the line of sight somewhere at about 25 yds. depending on the velocity of the bullet and the distance to the target.

Doesn't that depend on the height of the scope above the bore and the amount of recoil of the rifle?

 

[LHSmith]

dmoran
No disrespect intended just puzzlement.
If a bullet has not crossed the line of sight by the time it gets to 100 yds it never will.
From the moment a bullet exits the barrel it starts to drop.
To zero a rifle for 100 yds. the bullet must first cross the line of sight somewhere at about 25 yds. depending on the velocity of the bullet and the distance to the target.

I believe it's a matter of where he zero'd the rifle.....he zero'd for 168 gr @ 2800 and went to do a ladder test with 220's.....short answer = different bullets/ different zero's

 

[CaptainMal]

Just think it's barrel harmonics based on where the muzzle is in it's vibration pattern when the bullet leaves the muzzle.

Interesting enough I was shooting a Marlin 30-30 at short range today ( 100 yds) and my 170 gr. bullets - going slower- hit 3" higher than the 160 FTX bullets I was using.

At longer ranges that will change back to what you think is "normal". Don't think much of any ladder testing much less that 300 yards.

 

[LHSmith]

Where's the dude with the fancy graphics when you need him?

 

[Strut]

Another factor to consider is barrel harmonics. Barrels whip as the bullet passes and the vibration will be above AND BELOW the axis. You may have been on a downswing. The purpose of the ladder test is to find when the barrel is most stable or the node. The node is when the barrel is moving the slowest, that can be top or bottom of the swing. Once the node is found the scope is used to bring the point of impact up or down as desired.

 

[DuckHunt]

May I just add another obvious solution: if the problem is not your rifle being upside down, then try lowering your target. That should make it right. ???

 

[amlevin]

small barrel like a lightweight sporter or a heavy target barrel. Some will hit higher as the speed goes up, some lower.

Some things just need to be accepted for what they are without a lot of questions. Kind of like "why is the sky blue".


If you're able to get a nice accurate load out of your testing, why will it matter if "fast" goes up or down? Just adjust your scope for the new load.

 

[TroyMN]

Another factor to consider is barrel harmonics. Barrels whip as the bullet passes and the vibration will be above AND BELOW the axis. You may have been on a downswing. The purpose of the ladder test is to find when the barrel is most stable or the node. The node is when the barrel is moving the slowest, that can be top or bottom of the swing. Once the node is found the scope is used to bring the point of impact up or down as desired.

This happens to me also the ladder climbed down as charge increased. FYI my ladder was at 300yards. I will try to put a link to that thread http://forum.accurateshooter.com/index.php?topic=3796773.0
where I was told it was harmonics.
Troy

 

[BoydAllen]

If all of your loads' bullets are exiting on the upswing of the barrel, higher velocities will be pointing lower on the target. On the other hand, if the barrel has reached its peak, and is descending for all shots, higher velocities will print higher.

 

[lrgoodger]

Harmonics or barrel upswing causing it are understandable, but I'm with Hondo on puzzlement over this line of sight explanation. If you ignore harmonics and upswing and draw the paths of a slow bullet and a fast bullet exiting the barrel, the path of the fast bullet is ALWAYS above the slow one, no matter where your line of sight from the scope crosses the bullet paths. Assuming the scope is not readjusted and rifle placement is always identical, anything that causes the faster bullet to hit below the slower one at a given distance HAS to be the result of harmonics or upswing.

 

[Tim Singleton]

pretty sure dmoran is dead on
I noticed this when I first started loading at the range with my ppc. I would be zeroed an inch high at 100 as I began to through heavier charges of powder the impact began to creep down as I got hotter it would eventually shoot out my point of aim. the faster velocity would have the bullet flying a flatter trajectory. At 100 yards very few high powder rifles cross above the line of site before the bullet reaches 100 yds when 100 yd is the zero. Most scopes are at least 1.5" above the bore so at 100 the bullet doesn't cross the line of site. Now a 22rf or the like is a different story
After that I would site in for bullet impact below point of aim so as to not shoot out my site point

 

[lrgoodger]

Tsingleton, everything you say is true, but the flatter shooting, faster bullets creeping downward on the target are the result of the bullet getting out of the barrel sooner, before the barrel can rise from recoil as high as it did on the slower bullet. It has nothing to do with where the line of sight is or whether the bullet rises above the line of sight or not.

Envision this. We have a barrel poured into a six foot cube of concrete so it cannot rise from recoil or move from harmonics. The heavy load bullet path and the light load bullet path both start dropping the instant the bullet leaves the barrel. Assuming air density, temperature, gravity and wind are constant, the the faster bullet path will be higher than the slower bullet path at every point. Now draw target profiles at any distance you want on the bullet paths. You will see that the faster bullet hits every target higher than the slow bullet, and we have not yet even considered the line of sight because it is irrelevant. You can draw lines of sight to intersect the bullet path at any target and you will see that the two bullet holes on that target don't care where the line of sight is. The fast bullet is always highest UNDER THESE CONDITIONS, WHERE HARMONICS AND BARREL RISE ARE TAKEN OUT OF THE EQUATION.

If anyone can show otherwise, I will be in their debt and have to re-examine the laws of physics I was taught in engineering school. I have plotted two bullet speeds on the same ballistics program graph many times and the faster bullet trajectory is always above the slower bullet trajectory at every distance. When you throw in the scope zero distance to target, you get the numbers that show whether one or the other bullet might be above the line of sight, but the faster (flatter flying) bullet path is always above the slower one if they are plotted on the same graph.

All of this is contingent on the fast and slow bullets being the same weight, of course. You will get a slow heavy bullet hitting higher than a light fast bullet at longer distances because air density slows the lighter bullet faster.