7mm Rem Berger 180gr/168 difference?

[4bycamper]

Here's some in-depth material on these two bullets regarding BC, stability, and overall ballistic performance from a target shooting perspective. Note the analysis was not geared toward LRH, but much of the analysis is still very relevant.

-Bryan

Once again, thanks for the link. However that information begs another question. Still comparing 7mm 168 VLD with 180 VLD, if the lighter bullet is sent at higher and higher velocity and has a shorter time of flight, at some point it will not be diverted by the wind any more than the 180 VLD.

Can we know how fast it needs to go? Or another way to ask the same question: how fast will the 168 VLD need to be sent to have the same wind deflection as the 180 VLD @ 2800 fps, all other things being equal ?

Is this even a solvable problem? If not, is there a ballpark answer to the question? If I crank the 168 VLD up to 3200 fps, will that do it?

Thanks in advance.


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[AZShooter]

Yes you can figure out which one will outperform the other with a ballistics program. JBM makes a good one and it is free.

JBM

For what it is worth an earlier poster said he compared the two and got very similar downrange performance.

I decided to give it a try. Used the following data: G7 BCs: 168 VLD .316, 180 VLD .337
Elevation 2500 ft with adjusted barometric pressure of 27.32 , temp 65, humidity 30%, scope height 1.5", distance to chronograph 10 ft, wind speed of 10 mph with it moving 90 degrees to bullet flight.



I compared wind drift at 500 and 1000 yds:

Velocity for the 180 was your suggested 2800 fps drift at 500 10.8", at 1000 48.4"
When the 168 was 2940 fps it was VERY close drift at 500 10.7", at 1000 48.6"

I didn't compare drop or retained energy. Feel free to do your own comparisons.

 

[BryanLitz]

It is possible to calculate what velocity the 168 would need in order to match the wind deflection of the 180 (as AZshooter demonstrated).

However...

It's not a realistic comparison because you're talking about different chamber pressures. For example, it takes more pressure to get the 168 to 2940 fps than it does to get the 180 to 2800. Given equal chamber pressure (as the 180 at 2800), the 168 only achieves 2898 fps and the 180 is superior in terms of wind deflection.

Now if you jack the 168 up to 2940 fps to match the 180, the chamber pressure is equal to the 180 at 2840 fps, and the 180 is ahead again.

Nailing down the expected muzzle velocity of different weight bullets is an important part of any 'fair' ballistic analysis. It's hard to do because the chamber pressure assumption isn't always hard-and-fast. Sometimes the load isn't accurate at a certain chamber pressure and you're forced above or below the 'theoretical' velocity.

I hope this clarifies more than it confuses gun)

-Bryan