Same rifle, shooting 129 gr. SST at 2950 fps vs 143 gr. ELDX at 2700 fps. 100 yard zero with the SST's, tried a few of the ELD-X's and poi was like 2" higher. 20", 1-8 WC AR-10 off a bipod.

Who wants to tell me why?

I like this answer: "Lighter bullets at higher velocity spend less time in the barrel. Heavier bullets are slower and spend more time in a barrel that's recoiling upwards for a higher POI than lighter"

Who knows, I would attribute it to variations in harmonics or just how that barrel handles that bullet.

I have about 7 different loads that all shot to the same point out of my 270 win ranging from 90 grain hollow points going 3500 fps to 150 grain partitions going 2725 fps and 110 grain reduced ammo going 2500 fps. I shot them all at the range same day and wound up with a ragged hole about the size of a 50 cent piece at 100 yards after about 20 shots.

In my experience, this is the correct answer

Contrary to popular belief, it has nothing to do with the gun's recoil. The bullet is already long gone by the time the gun is moving backwards. This is even true with slow-moving pistol calibers.

The trajectory of the bullet changes with velocity. You can check this with any ballistic calculator. A faster bullet will have traveled farther forwards in a given period of time, and thus will reach the apex of its travel farther away. Taken at any distance before then, it will appear to hit lower on the target than a slower bullet.

Im not sure i believe that either.

If you change your grip on a pistol/rifle from loose to trying to keep the rifle from moving at all costs it will change the point of impact.

Yup. Harmonics

And this is what hand loaders handload for. Getting the right charge to work with the barrel's harmonics for "X" bullet. Looks like this rifle just agrees with the 143's, if they are heavier and hitting higher. Bullet probably leaves the barrel at the apex of the sine wave. All is well, as long as it hits consistently.

Interesting. I'd like to see a trajectory line for these two, side by side. That would prove it.

What ever it is doing, it does it exactly the same every time with the SST's. I shot it for drop a couple of weeks age at 200, 300 and 400 yards. It worked on a live target the next day at 280 yards. Held the 8" I had from the day before at 300, dead pig.

Working up a load with using the same manufacturer, exact model and grain of bullet, you will find that one load may be 2" high and to the right and then another load be 2" low and to the left. What you are doing above is changing grain and bullet styles also , no telling how many different ways it will fly.

Many have chimed in an I tend to agree with barrel harmonics.

Since getting my magnetospeed, I have noticed a general trend that higher velocity bullets shoot higher on paper. However, I've seen a bunch of doozies. Putting a guesstimate, like 60% even with the same bullet shooting the same load do speed vs elevation. That's not enough correlation to be meaningful to me.




Attached are graphs from 2 loads I have data for. The ballistic calculation is from the Berger website. You can input the data yourself i you;d like. I know for both loads the 300 yard is pretty spot on and the 600 for the 178 is confirmed from me in terms of the drop.
You can see the lighter 155 with 300fps more velocity reached 1000 yards faster.

While harmonics do have a tendency to affect zero in a big way, the general trend of heavier bullets hitting higher at close ranges is not due to this. Ballistic calculators do not account for harmonics- only the mathematics of trajectories. The numbers don't lie.

Seen plenty of heavier bullets land lower at 100 yards, also.

Ballistic calculators are very helpful thing, and I use them weekly. But they, QuickLoad, published load data, chronographs and a host of other things do not replace rifle range testing and documentation of said testing.

As Captain Ron said "if anything is going to happen, it is going to happen out there."

Long thin barrel, short thick barrel, same twist rate, same exact ammo, I expect different POI on all of them. Even barrels of the same finish length, but with different contours are likely to have varying POIs. All equals harmonics.

Have shot three different 130 grain loads from my old .270 Win at the same target, all factory ammo. Two shot almost to the same place at 100 yards. One wasn’t even on the target. I don’t think you could predict where any specific load would print with any sort of accuracy. Gotta shoot it to find out. Although, if you could figure it out, you could theoretically sight in a rifle in the living room without actually shooting it. That would be pretty cool.

Preach!

Heavier/slower bullet hitting higher than a lighter/faster bullet at 100 is barrel harmonics provided that everything else is the same.

I hate to say it but you guys are missing the point here. Obviously a load going 1500fps vs 3000fps is going to have a different vertical POI due to a difference in velocity. That is not something that is chalked up to barrel harmonics, and is not what OP was asking about.

Obviously his difference is smaller, but the same trend is there. I can replicate this with my pistols, my rifles, a ballistic calculator, and probably even a crossbow if I had one.

Exactly. That is what we were doing. Windage was good, and it did group decently.

One of two points at which the barrel is stationary along the harmonic wave.

Just curious if it's possible a given load produces a bullet that leaves the barrel at the bottom of the harmonic wave? If so, you would think this would create a somewhat lower POI.

I think you're missing the point, sir.

In factory ammo, as well as hand loads a lighter bullet almost always has a higher muzzle velocity. Therefore it should print higher on paper. I lust finished a ladder test 30 minutes ago because of this. Faster, equals rise on paper. When ammo has a heavier bullet AND is probably slower, but prints higher than a lighter faster bullet, that is due to barrel harmonics. OS&W has found some ammo that is leaving his muzzle at the apex of the sine wave, and good for him. But changing ammo lot numbers can (and probably will) print somewhere else from the 100 yard zero. Same bullet, new powder lot, new velocity, new relationship with the barrel's harmonics.

Want to go on record as saying this is absolutely not true. Recoil management (how you drive the gun) ABSOLUTELY influences POI. It may not be happening in this instance, but to claim it's not a possibility is asinine.

You should plug this into a ballistic calculator and test if this is the case. Change your velocity by 200fps, set your increments to as small as they can get, and check the ballistics tables. It just isn't borne out in reality. Edited to add- This is true within certain distances. A ladder test at longer distances like 200yds may have lighter bullets printing higher if their balance with BC means that they haven't dropped as much.

Like I said, this is a repeatable shift with anything. If it has a sight that is over its bore and it uses a parabolic trajectory, this is predictable and repeatable. A shift due to harmonics instead would not be predictable.






I'd encourage you to watch this part of the video (1:31) at 1/4 speed. Notice how the bolt hasn't even started cycling and the bullet is long gone. This is somewhat related to a previous thread where shooters claimed that the last round in an AR15 shoots differently because the bolt cycles differently, and this video should also debunk that.

I'm not saying that your actions with the rifle don't influence POI. But if you are getting more than an inch of shift at 100yd by changing from sitting to prone, for example, you are dealing with shooter error in the form of parallax or technique. My handguns don't shoot 2" higher at 25 yards with a slower load because my gun is already tilting that much farther upwards.

All of these reasons given make some sense, and I appreciate all the responses. My reason for asking, if I need to source a new load, what characteristics should I try to duplicate to so stay as close to what I have dope on. Velocity, OAL, wt., etc....Sounds like none of them. Since it did group a different load decent, only higher that tells me I just need to find a good supply of whatever I settle on, like 200 rounds minimum, (This is a hunting rifle, 50 rounds a year is a pile of pigs, a few deer and a handful of coyotes) shoot a new group and move on. I have a 200 + rounds of this Hornady, I'll be good for a while. Never too old to learn. My take away so far is some, if not all of the reasons are at work.

You're leaning on calculators and the internet too much.

Shoot more rifles, more barrel contours, more bullet weights, more barrel lengths, more muzzle devices, in more weather. Produce volumes of real rifle range data, and I might listen.

I mean this is coming entirely from my own experience, and I'm using the ballistic calculator as way to explain something that happens both in theory and on the range. You aren't the only one with rifle experience, but you are the one who hasn't provided any real data to back up his claim. You do seem to be thinking in terms of a ladder test at long ranges. It's true that all other things held equal, a higher velocity bullet will impact higher at long ranges.

I'm talking specifically about close ranges where the bullet is still on the rise. For example, OP is shooting at 100 yards where most bullets will still be rising. Go ahead and try this the next time you head out to the range. Take your two best shooting loads for two bullet weights, and shoot them at like 50-100 yards. It doesn't even matter what distance you're zeroed for. 100% the slower bullet will shoot higher. Picking two good loads removes your idea of harmonics from the equation, and leaves it solely based on differences in trajectory due to velocity.

“It's true that all other things held equal, a higher velocity bullet will impact higher at long ranges. “

“ It doesn't even matter what distance you're zeroed for. 100% the slower bullet will shoot higher.“

Um, Hick.....which is it?