Hi,

Wondering if someone can offer some advice on this scenario: I was at the range last week re-sighting a rifle after changing scopes. I zeroed it with factory Federal 150gr rounds, then switched to 150gr Hornady SP reloads. Groups were about the same size, but the POI moved about 8" to the right with the reloads. Same thing happened when I tried 165gr Nosler BT reloads. Any suggestions?

Thanks,
Bruce

Sounds like each load was progressivly hotter and the recoil is in effect rotating the rifle around your center of gravity.

Your barrel is somewhat of a "tuning fork". It is moving as the bullet comes down and exits. A couple weeks ago I was at the range and had some ammo that was full length sized and some that had been neck sized and took a little effort to close the bolt. Other than that they were the exact same recipe..bullet and powder. The results were 2 very nice groups about 12" appart at 200 yds. I wouldn'have believed it if I hadn't seen it but somehowthe "harmonics" were changed by tight fit verses loose fit.

vertical difference is velocity...

zero a gun at 100 yards and the load that hits LOWER is going faster (yes, sir.. faster) due to , as dustoffer phrased so well, dwell time under recoil

left/right is bullet bearing surface

jeffe

quote:

Originally posted by jeffeosso:
vertical difference is velocity...

zero a gun at 100 yards and the load that hits LOWER is going faster (yes, sir.. faster) due to , as dustoffer phrased so well, dwell time under recoil

left/right is bullet bearing surface

jeffe

This goes against everything that I have seen for the last 55 years.

quote:

Originally posted by jeffeosso:
vertical difference is velocity...

zero a gun at 100 yards and the load that hits LOWER is going faster (yes, sir.. faster) due to , as dustoffer phrased so well, dwell time under recoil

left/right is bullet bearing surface

jeffe

Sounds like one of my head scratchers lately. I have compared the same load on different days in my 300 SAUM with 165TSXs. The 63 grain load of H4350EXT shoots 1/2" higher than the 64.0 gr load and the 64.0 grain load is much tighter.
The Chrony says the 64.0 gr load is faster but it shoots 1/2" lower consistently but it also shoots a 1/2" group.

quote:

zero a gun at 100 yards and the load that hits LOWER is going faster (yes, sir.. faster) due to , as dustoffer phrased so well, dwell time under recoil

I have simply changed bullets while using the same powder charge,with the same velocity according to my chronograph,yet the point of impact moved 2-1/2" vertically.The partitions struck lower yet the average velocity was virtually identical to that of the ballistic tips.

quote:

Originally posted by jeffeosso:
vertical difference is velocity...

zero a gun at 100 yards and the load that hits LOWER is going faster (yes, sir.. faster) due to , as dustoffer phrased so well, dwell time under recoilleft/right is bullet bearing surface
jeffe

Does that only happen in Texas, Jeffe?

I think you have me by a year or so , Savage 99 but Ditto. roger

What Jeffe states (lower impact with higher velocity loads) is fully possible. I don't know if it is predictable, but it is certainly possible. Face it, where the bullet impacts to a large degree depends on the position of the muzzle at bullet exit. We know barrels vibrate, and excatly where we are on the curve (assuming we approximate the vibration to a sine curve), will have a great say in where the bullet impacts. I have found this largely unpredictable. If you want two (or more) loads to shoot to the same POI, you need to try it out. Maybe it will work, maybe it won't, some load tuning *might* help.

What the original poster experienced is not so strange. After all, it is a comparison of factory vs handloads. Who knows what powder is used in the factory loads, burning rate, charge and resulting barrel vibration?? You would have to be VERY lucky if this matched POI of your handloads. It sounded like your handloads (150 and 165 grs) were better matched, perhaps you used the same powder with similar (not identical) charges??

- mike

quote:

It sounded like your handloads (150 and 165 grs) were better matched, perhaps you used the same powder with similar (not identical) charges??

All handloads that day were using AR2208 (equivalent to Varget), so yes they were all same case/primer/powder type, with projectile and quantity of powder the only variable.

Bruce

An 8" shift with just a change in bullets is a lot. Have you checked to make sure everything is tight?
Is this shift repeatable?

quote:

Originally posted by mho:
What Jeffe states (lower impact with higher velocity loads) is fully possible. mike

Yes! Possible! But to come up with a ballistic LAW that this is what happens when*** is the disputed point. The barrel is not so much in a linear resonance as it is elliptically resonat. When the bullet leaves the barrel it can slightly go left , right or up and down. There is a lot that comes into play that determines the magnitude and direction of the excursion. A great gunsmith is not necessarily a knowledeable Ballistician. roger

quote:

Originally posted by bartsche:
... When the bullet leaves the barrel it can slightly go left , right or up and down. There is a lot that comes into play that determines the magnitude and direction of the excursion. ...

Excellent response.

When you add Faster burning Powders relative to Slower Burning Powders into the equation, different Intensity Primers, Barrel Stiffness, etc., it helps understand "Why" Rogers response is correct.

Good hunting and clean 1-shot kills.

quote:

Originally posted by bartsche:

quote:

Originally posted by mho:
What Jeffe states (lower impact with higher velocity loads) is fully possible. mike

Yes! Possible! But to come up with a ballistic LAW that this is what happens when*** is the disputed point. The barrel is not so much in a linear resonance as it is elliptically resonat. When the bullet leaves the barrel it can slightly go left , right or up and down. There is a lot that comes into play that determines the magnitude and direction of the excursion. A great gunsmith is not necessarily a knowledeable Ballistician. roger

Roger, if you want to quote me on a subject, it is probably best if you complete the quotes. With regards to muzzle velocity and predictable shifts in POI with increasing velocity, I stated (bolding added):

quote:

Originally posted by mho:
What Jeffe states (lower impact with higher velocity loads) is fully possible. I don't know if it is predictable, but it is certainly possible.

I don't see anything in that statement claiming anything about a LAW (or predictability) of POI with changing muzzle velocity. And I'm certainly not going to claim I understand the complex vibrations even of a single barrel with a single load.

Btw, I used the abstraction of sine curve harmonic vibrations to describe and understand the problem. As you will appreciate, that is different from attempting to quantify or predict the exact outcome of a change in loads or barrel in a real world situation.

- mike

It has alway been my understanding that the faster=lower POI was applicable in handguns due to dwell time of the round in the barrel vs. recoil.
My experience has been the opposite for rifle rounds.
Not disputing what was said, just that experientially, that has not been the case for me.
Agree with mho in that the barrel is in a state of harmonic vibration and where the bullet exits the end of the barrel determines the place it ends up (along with the powder charge and bullet weight)

quote:

Originally posted by jeffeosso:
vertical difference is velocity...

zero a gun at 100 yards and the load that hits LOWER is going faster (yes, sir.. faster) due to , as dustoffer phrased so well, dwell time under recoil

left/right is bullet bearing surface

jeffe

I've seen this before but only in one particular rifle,With my Swedish AG42 as powder charge and velocity increased bullet impact actually moved down! and I'm not talking in little tiny increments either.

Every other rifle I've owned has been the exact opposite.

quote:

Originally posted by mho:
[QUOTE]Originally posted by bartsche:
[QUOTE]Originally posted by mho:
What Jeffe states (lower impact with higher velocity loads) is fully possible. mike

I don't see anything in that statement claiming anything about a LAW (or predictability) of POI with changing muzzle velocity. And I'm certainly not going to claim I understand the complex vibrations even of a single barrel with a single load.

No foul intended, mho; The use of the word LAW was directed at the original statement, not yours, regarding velocity affecting point of aim as a rule. I guess that sometimes when I put words together it doesn't always reflect the message I'm trying to get across. Truely sorry if I've slighted you. roger

quote:

Originally posted by Savage99:

quote:

Originally posted by jeffeosso:
vertical difference is velocity...

zero a gun at 100 yards and the load that hits LOWER is going faster (yes, sir.. faster) due to , as dustoffer phrased so well, dwell time under recoil

left/right is bullet bearing surface

jeffe

This goes against everything that I have seen for the last 55 years.

I agree, when working up a load for a 308VS I noticed as the load got hotter the poi went up and to the right. Jay

There is a no magic force here; the bullet travels in a straight line until affected by gravity.

If your barrel is perfectly flat, meaning horizontal to the ground when the bullet leaves the barrel in relation to a target that is at the same height. The bullet will travel on that line until gravity has an effect on it. Gravity will start to pull you bullet to the ground immediately as it leaves the barrel. The only force your bullet has to prevent this is its velocity. The higher the velocity the further the bullet will travel in that line before it is pulled to the ground by gravity.

If you are sighted in at 100 yards then your gun must be angled slightly up. Your bullet will continue to travel in that line until gravity has an affect on it. Pulling it to the ground, ever faster as velocity decreases.

Speed is not a force that changes the direction of an object in motion; it just increases its resistance.

If you want to say that velocity has an effect on aerodynamics, which would change with every variation of bullet. That is possible.

The way I see it is barrel vibration can affect the line of travel but once the bullet leaves the barrel, velocity will not be the determining factor to a lower POI.


Simdow

quote:

Originally posted by bartsche:
No foul intended, mho; The use of the word LAW was directed at the original statement, not yours, regarding velocity affecting point of aim as a rule. I guess that sometimes when I put words together it doesn't always reflect the message I'm trying to get across. Truely sorry if I've slighted you. roger

Roger, no offense taken. Thanks for being a friendly partner in a good argument.

- mike

Check with someone who shoots on a regular basis the old 45/70 round and uses anywhere from 300 grain jacketed bullets to 525 grain cast lead bullets at various velocities and he will very quickly tell you about "dwell time." The spread in elevation is much greater than mentioned here w/ a modern cartridge. Yes, the heavy slug will impact much higher than the lighter slug and require much change in sight settings to compensate. Recoil related and time elapsed while projectile travelling down the bore will result in different point of impact, i.e. higher on target face.
Imagine if you will a yard stick to the side of the muzzle and being able to measure the highest point of upward travel due to recoil. Whatever than measurement may be, it will be less distance travelled (upward) by the lighter load simply due to recoil produced by the lighter projectile. 45/70 is extreme example but depicts the situation originally inquired about from the outset.

There are fairly recent test results that would state that resistance to the atmosphere in flight has much more to do with projectile travel than previously thought and to put it quite simply, some bullets just fly better than others due to various reasons. That can account for some deviation as well. Unfortunately ol' Napoleon is not around to help out here, for he was known as a superb mathematician and ballistician as well. He made his mark with artillery calculations and later strategy in the manly science of war.
He must have screwed up somewhere for believe he ended up on some island inprison???