Range Report Performance of different bullet BC's

[longeyes]

Just trying to understand the advantage of using a 208 over a 178gr amax in my 30-06. When I compared the 178gr load I am currently using to a 208 load and plugging the data into JBM, I would gain less than 50yds before going sub-sonic and only gain .7mil of drop at 1000yds. Considering increased recoil and other dis-advantages of heavier loads. What would be the advantages?

 

[rijndael]

Re: Performance of different bullet BC's

What do the wind numbers look like?

 

[AQC440]

Re: Performance of different bullet BC's

I think you started to answer your own question.
Several small-insignificant differences linked together start to add up to an advantage.
-.7 mil drop,50 ( ? ) more yards before becoming sub-sonic, less wind drift and more energy added together could be the difference between a hit or miss , 5 in a tight group ( at long range ) or an animal cleanly taken.
In addition, to put it in perspective either one of your high BC 30-06 loads smoke a 150 gr. 300 Win Mag factory load.
Just my .02

 

[longeyes]

Re: Performance of different bullet BC's

The wind #'s are; 208gr -- .1mil/100yds with 10mph
178gr -- .2mil/100yds with 10mph

So I guess that pretty much answers my question. Not lots of gain for range but a major difference in bucking the wind.
Thanks for the inputs.

 

[BryanLitz]

Re: Performance of different bullet BC's

Also consider velocity retention.

You mentioned the 208's only get 50 yards further before going subsonic. That doesn't sound like much, but consider how much faster the 178's started.

Same goes for trajectory. The 208's will have a slower muzzle velocity but end up flatter. Even if it's only a little flatter, this is remarkable.

A better wind comparison would be to look at how the deflection compares at 1000 yards in a 10 mph crosswind. I suspect there's some rounding that went on for your 100 yard numbers.

The 208 really us much better than the 178. It's BC isn't just higher because it's 30 grains heavier; the 208 is also a much lower drag profile than the 178 which is the same ogive and BT as the 168 and 155 Amax. The 208 is a very well designed bullet; in fact it's the best 210 grain class bullet in .30 caliber (in terms of ballistic performance).

Kombayach recently published an awesome article on loading all the 210 class bullets in 308. I'm sure a quick search can turn up the article if you're interested.

Take care,
-Bryan

 

[MontanaMarine]

Re: Performance of different bullet BC's

Here are a few comparisons at realistic 30-06 velocities from a 22.5" bbl. These are in my local atmosheric conditions.


178 AMax 2875 fps, and 208 AMax 2700 fps:

range/velocity/energy/10 mph drift (rounded .25 moa)/drop (rounded .25 moa)


178 AMax: 600 yds/1979 fps/1545 ft-lbs /3.5 moa/12.25 moa
208 AMax: 600 yds/2025 fps/1895 ft-lbs /3.0 moa/13.00 moa

178 AMax: 1000 yds /1493 fps /881 ft-lbs /7.00 moa/28.50 moa
208 AMax: 1000 yds /1639 fps /1240 ft-lbs/5.25 moa/28.50 moa

178 AMax: 1500 yds /1083 fps /463 ft-lbs/12.25 moa/61.25 moa
208 AMax: 1500 yds /1251 fps /723 ft-lbs/9.25 moa/ 56.00 moa

If there are disadvantages to the heavier bullet, I haven't discovered them yet.

 

[Falar]

Re: Performance of different bullet BC's

208gr advantages:

Better BC and thus flatter trajectory and more retained muzzle energy at long range as well as less wind deflection.

 

[longeyes]

Re: Performance of different bullet BC's

Thanks guys for your responses---I read Bryan's article on applied ballistics then went back and reviewed my numbers on the JBM calculator---turns out that I entered incorrect numbers, which gave me bad read outs. The good part is that I gained a lot of new understanding of ballistics. and have some new ideas to try out.
Gonna do some work-ups using 208's and RL-22.