Load Change/Sight Adjustment

[Homes Outside]

Curious if there is a way to figure out how many clicks to adjust my scope for different rifle cartridges without the need to start from scratch. My scope is Mildot.

I have my rifle sighted in with federal blue box 100 gr soft points 2960 fps BC 0.355 for a 200 yard zero

I would like to adjust my scope so that federal 55 grain ballistic tip 3850 fps BC 0.276 is zeroed for 300 yards.

Yes all the numbers are quoted off the box and I understand that it all needs to be verified. Just curious if there is a formula or a website or something that makes this easier than starting back at 50 yards and working my way further out on paper as I go.

Thanks for any help and advice

Homes Outside

[colroggal]

Shoot the 55's at 100yds and adjust. Windage may vary as well, but you should be on paper, and more than likely just a few clicks off. Remember, every load can and will shoot differently in every rifle.

Colin

[Dick284]

Shoot and see is the only 100% way of knowing.

You could see lateral shifts in point of impact as well as vertical shifts as well.

Sometimes the point of impact may not go in the anticipated direction as well.

All of this is because of barrel harmonics.

[densa44]

Barrel harmonics are the answer to many rifle impact questions.

Shoot a few boxes and let us know.

[Big Sky]

The only thing that I would add to the above comments is to write down the change in POI between the two loads.

When you switch between loads use this information to adjust your scope.
Then, verify your zero just to be sure. If your scope has precise adjustments, this should cut down on the number of rounds it takes to sight in when you go back and forth between loads.

[Flight01]

Originally Posted by Big Sky

The only thing that I would add to the above comments is to write down the change in POI between the two loads.

When you switch between loads use this information to adjust your scope.
Then, verify your zero just to be sure. If your scope has precise adjustments, this should cut down on the number of rounds it takes to sight in when you go back and forth between loads.

This. You need to adjust as it will not likely just hit higher but may be off left or right. Barrel harmonics are a funny thing and sometimes are dramatic

Like Big Sky said , write it down and next time you switch just get to the new settings and still shoot to prove on paper.

[elkhunter11]

Originally Posted by Flight01

This. You need to adjust as it will not likely just hit higher but may be off left or right. Barrel harmonics are a funny thing and sometimes are dramatic

Like Big Sky said , write it down and next time you switch just get to the new settings and still shoot to prove on paper.

And the point of impact of the lighter bullet may be lower at 100 yards

[Homes Outside]

Thanks too all. Never even considered barrel harmonics. Will need to do some more reading to understand this. Writing down click adjustments is a really good idea for going between loads.
Will be interesting to see if there is any lateral adjustments or not.

[dogslayer403]

Originally Posted by Homes Outside

Thanks too all. Never even considered barrel harmonics. Will need to do some more reading to understand this. Writing down click adjustments is a really good idea for going between loads.
Will be interesting to see if there is any lateral adjustments or not.

No two rifles will do the same thing wish there was a magic formula but there is no replacement for field testing loads and ammo. Your lighter bullets may hit low may hit high maybe left maybe right will all be dependant on your particular rifles harmonics

[Flight01]

Originally Posted by elkhunter11

And the point of impact of the lighter bullet may be lower at 100 yards

Correct. Nothing is certain. Harmonics are funny that way. Did have some 150 grain 308 hitting lower than the 180's at 100 yards when testing ammo

[Homes Outside]

Just curious does anyone know if barrel harmonics change when shooting in different temperature? I understand that a bullet can have a slightly different flight path due to air density etc. If harmonics do change from temperature is it drastic enough to make a huge difference in point of impact say -15 compared to +5

[elkhunter11]

Originally Posted by Homes Outside

Just curious does anyone know if barrel harmonics change when shooting in different temperature? I understand that a bullet can have a slightly different flight path due to air density etc. If harmonics do change from temperature is it drastic enough to make a huge difference in point of impact say -15 compared to +5

The burning rate of the powder can change with temperature; which results in a change in pressure, and a change in velocity, which will effect the harmonics.

[Pathfinder76]

Originally Posted by Homes Outside

Thanks too all. Never even considered barrel harmonics. Will need to do some more reading to understand this. Writing down click adjustments is a really good idea for going between loads.
Will be interesting to see if there is any lateral adjustments or not.

Don't read. Shoot.

[West O'5]

Originally Posted by elkhunter11

The burning rate of the powder can change with temperature; which results in a change in pressure, and a change in velocity, which will effect the harmonics.

This^^....plus the fact that cold air is denser then warm air will effect downrange velocity.Probably negligable difference at 100,200,even 300y,esp for hunting applications,but if your striving for sub MOA/PRS accuracy,temp changes everything,and not just ambient temp,but actual ammo temp which may or not be the same as ambient temp...ie;ammo stored in your pocket vs attached magazine,ammo exposed to radiant warmth from sun,cold bore shot vs ammo that's allowed to warm up in a chamber etc etc.
Again,it's really not THAT much of a concern until you stretch it to extended range,but at LR and XLR especially,temp variation will have a noticeable effect,and the more extreme the temp variance,the more difference it makes beginning with MV thru harmonics and on to wind deflection and drop.
A tack driving sub MOA load developed in +20C in July is not going to perform the same in -20C in Nov at long to extreme long range,even with powders that are more resistant to temp differences,the air itself is denser.

[Lefty-Canuck]

Originally Posted by chuck

Don't read. Shoot.

Exactly.

LC

[gitrdun]

Originally Posted by elkhunter11

The burning rate of the powder can change with temperature; which results in a change in pressure, and a change in velocity, which will effect the harmonics.

Actually elk, you are partially correct. The barrel harmonics themselves are not affected by temperature, pressure, etc. The natural frequency (resonant frequency of the barrel) is defined by it's mass, shape and material. The natural frequency of the barrel can also be affected by imparting a pressure point which drives the frequency upward. All that being said, and no mods made to the barrel, the harmonics will remain the same. What does change the point of impact is bullet velocity. A change in velocity means that the bullet will exit the muzzle at a different point in time. Such as when the muzzle is at a node, an anti-node or somewhere between the two. However, if you were to take a shot with your barrel leaning on a fence post, you would then affect the barrel harmonics. Not so if you lean the gun stock on the post (providing that it is free floated of course).

I'm not talking out of my hat. I am a certified level 3 vibration analyst with 28 years in the field, troubleshooting and resolving machinery vibration. Which includes de-tuning machine components away from resonance or natural frequency.

[gitrdun]

Originally Posted by Flight01

Correct. Nothing is certain. Harmonics are funny that way. Did have some 150 grain 308 hitting lower than the 180's at 100 yards when testing ammo

That is because the 150's obviously fly faster than the 180's, meaning that they leave the muzzle sooner and at a different node location.

[TBark]

Took me a while to figure that out, lighter one hits lower by a few inches at 150 yds.
I have Accubonds and ELDX 160-162 gr hitting very close to ea other, and Barnes 160, basically a coin flip, very close at 150.
I just don't shoot much further anyways. But the Berger 168, wow, 5-6" to the right of the others at 150.
I'll be deciding on which one to go with soon for this year and fine tune.

TBark