co efficiency - 6mm

[Link]

Hi Let me see if I can put my question in print.

It seems to me that the 6 ppc and 6 br are effected by the wind more than the .30s like a 308. I was told that the 22 br is much better in the wind also. If so why are the 6MMs so popular? What do you think?

thanks Link

 

[mikecr]

In the end, there all even.
But you have to crunch all the pros & cons into something that suits your needs.
That's what everyone does, and why there are so many different paths.

 

[jeffreybehr]

In the end, there all even.

Did you mean to write 'they are all even'?

Either way, they are NOT all even in the end. There are significant differences in a bullet's ability to resist being deflected by wind, and,I believe) the concensus is that the best larger-diameter bullets work better than the best smaller-diameter bullets.

Of course there are other considerations, but that's not what Link asked about.

 

[Forum Boss]

I think what MikeCR may mean is that you look at a given bullet's BC and factor in how fast you can shoot it, then the ballistics programs can predict how far it will drift in a crosswind.,You do need to confirm the BC with "real world" testing at the range of course.)

You can have a 6mm bullet/speed combo that outperforms a 30 Cal set-up, or vice-versa.

Now, add into the equation the observation by many long range shooters that, when conditions get really bad, the big heavy bullets may seem to fly more consistently than the 6mms. Why, nobody is quite sure. It may have to do with performance in fishtailing winds. Mind you, this is part of the "voodoo" of the long-range game. BC and velocity should "tell all". But many folks think there is more involved and the big, heavy bullets will do better in the wind than a 6mm set-up even if the ballistics and crosswind drift appear equal on paper.

On the flip side, you have to look at vertical consistency. In calm conditions, Jason Baney has achieved tight verticals with his BR that beat just about anything he's seen with bigger bullets. The ballistics tables can predict vertical drop caused by drag. They don't tell you,assuming ES/SD are equivalent) which bullet/velocity combo will hold tighter vertical on the target.

There are a lot of factors to consider. That's why you see a wide range of cartridges being used successfully at 1000, from a standard 6BR to the 30-.338 Lapua Magnum that recently sent a world record in Ohio.

---

Regarding the 6PPC. That cartridge is normally shot with short, low-BC flatbase 60-68gr match bullets. These have exceptional accuracy, but they WILL move more in a given crosswind than a longer boat-tail design, when pushed at equal velocities. But again, you have to add in the inherent accuracy factor. At 100/200 yards if the shorter bullet is much more likely to group in the "zeros", so far it remains the first choice in BR at those distances. The general consenses is that the better performance in the wind you may gain with the longer, higher-BC bullet, is offset by the accuracy you lose, at least out to 100/200.

 

[EricStecker]

If so why are the 6MMs so popular? What do you think?

thanks Link

Link,

It all comes down to compromise. Nothing works THE BEST in all situations. Heavy bullets do well in the wind but have more recoil. Light and fast bullet have less recoil but are more affected by the wind. The 6mm seems to be best the middle ground. You get a heavier bullet than the 22 cal while at the same time less recoil than the 30 cal.

There are other factors,and calibers) to consider but at the end of the day it seems the 6mm wins a lot of matches.

In the 80's Bill Davis and Dr. Lou Palmisano were asked to come up with a cartridge/bullet combination that would have a better trajectory than the 30 cal 168 gr being used at the time by the USAMU. Medical tests proved that points were being lost by the USAMU shooters due to the accumulated affects of recoil.

Bill and Lou were probably the sharpest minds at the time on this subject and they settled upon the 6mm,220 Swift case opened up to 6mm called a 2" PPC and the 6mm 105 gr VLD). This cartridge/bullet combination solved the recoil problem and outperformed the 168 gr trajectory. If it was good enough for Bill and Lou there had to be a reason that they could support with their extensive experience and knowledge,not to mention the fact that it worked).

Regards,
Eric

 

[Link]

Thanks guys there is some good info there.

Let me see, do I want to put my slicks on or my drag tires :}