Ballistics G1 & G7

[Don A Parsons]

I'm starting this thread too get a better grasp in this area as I begin my journey into long range shooting,,,, "not hunting."

BC things were not part of my game harvests in general, well only part of it let's say. So I'll cut too the first chase.

G1 & G7 I partly under stand, so here's my questions.

G7 differences of let's say .300 and. 315 would make ruffly how much difference over let's say 1000 yards / 900M.

There must be a tool too calculate this.

Next question.
G1 differences of .500 compared too a bullet that has .600BC would be different in what way.

I ask this as I'm doing a F Class build coming up.

There will be more questions too as.

Thanks from Don

 

[Don A Parsons]

So the puzzle is bullet selection.

6.5, 7mm, or 30 cal.

I see benefits and disadvantages in each.
The SD and BC play roles on these calibers as well as others, but looking at the bullets on the bench tells me very little.

The 6.5 143gr ELD-X bullet gets a G1 @ .625 & G7 @ .315

7mm 175gr ELD-X bullet gets a G1 @ .689 & G7 @ .347

30 Cal 175gr ELD-X bullet gets a G1 @ .535 & G7 @.271

Yes I know that they are different grain bullets, sectional density, diameter, length, and probably velocities.

Write up's mention that the smaller caliber bullets have less frontal area as larger bullets have more.

They say that the smaller bullets get better penitration because of this.

Is the few thousands of a inch in diameter from 6.5 too 30 caliber that big of a factor.

My mind in the close range harvest field tells me it's no big deal since all these calibers and others have harvested critters all around the world.

Maybe this BC thing has part too play in game harvests, but probably more so at long range.

So how much difference is too much.

I would think a semi pointed round nose will not perform like a full on pointed bullet,,, but when all the bullets are pointed,,, will they not be close too the same target grouping at 600M or 900M / 700 too 10000 yards.

How much difference in issues would there be from 6.5 G7 .315 too a 30 cal G7.271

My noodle tells me that at long distances like this so long as both bullets do not drop below sub sonic at 1130 ft-per second,,, or trans sonic at 1340 ft-per second.

I'm guessing that this G1 & G7 BC plays a bigger role when the above bullets fall into this category.

Even then, my mind tells me that both longer and heavier bullets work better at extra long distances in the 1000 too 16 or 1700m range /// 1100 too 1800 yards.

Or the mile too 2 mile stuff,,, not the 1000 yard category.

What am I missing, where is the info too compare BC G1 & G7 values between bullets.

Lots of post too go as I narrow down this puzzle with in my mind.

Don

 

[Don A Parsons]

Time too put up some examples of over all spread between some bullets.

Let's say the spread of .044 BC between 2 bullets is present.
Again a 6.5 bullet with BC of .312 in the G7 category,,, and a 30 cal of .271 in G7.

My mind tells me that .044 is so small when looking at doing a build.

Yes that its purhaps wize too pick the bullet with the best BC, but let's say in this example that we are going after large game all the time, or want too shot long distances in the mountains where winds are a constant.

Is .044 BC even a factor. What about .022 in the low spread or .100 BC difference.

Where does a person draw the line in how much BC difference is too much.

My planned rifle build is 30 caliber because I like that size of bullet, lots, and I mean lots of people are "suggesting" too me too look at the 6.5 and 7mm since they blow the 30 caliber bullet right out of the water.

Yes that some of this is partly true, but how major is this if I harvest game up close well with in 40 too 140 yards with options too 2 or 300 max.

Long distance shooting too me is at metal gongs and F Class match targets from 4 too 900M, does this mean that my 18 1/2 lb FTR 308 will not be able to do this with 178, 200, and 212 grain bullets.

I just can't rap my head around owning 2 different caliber rifles that are different in caliber size as I only shot 30 cal bullets only.
I'm not about too change since I'm at the stage in life that does not allow for this.
Yes that I have a 30/06 and a 308, but they are both 30 caliber bullets.

Hunting bullets on top of that since they work for F Class,,, and they work good as I've been lucky with the 10" groups at 1 km / 1000 meters or the 1100 ish yards.

I just don't see a 6.5 or 7mm in my category, this is why I ask about this spread of average BC that are small between bullets.

I'm sure that .100 and .200 BC show definit differences but is .050 BC also too much spread.

What would this BC of .050 look like down range I'm asking.

Is it 4" difference at 1000 yards/ 900M or much larger in the 8" to 10". Or is it smaller.

I hope that there is some way too find this out, I realize that BC is about how well a bullet travels threw the air, and the effects of wind that effects the bullet while it's on its way too the intended target.

My question is still complicated, but .050 BC is a good example too work with since it is a some what round number and it like a difference between not only the 3 bullets I'm looking at,,, but other caliber bullets that other folks are wondering about.

Turning BC into inches of "possible" spread at 500, 750, and 1000 yards would help my mind see this in a more practical way.

Don

 

[dok7mm]

Just enter the possible choices in a ballistic calculator at varying distances, wind speeds and velocities. Then make a spread sheet to compare the different options for drop and wind bucking abilities.

 

[Don A Parsons]

I was thinking this last night in my sleep.

Awesome idea.

I add the values into the JBM calculation chart and use that as a base model in comparison.

Another plan is too do real time tests using different styles of 30 caliber bullets of the same weight at a set distance.

The 1000 yard/ 900 meters since this is the distances I'll target shooting at.

Nothing like real time testing as I need too burn off a few barrels this winter. LOL.

Lots of shopping today as I pick-up the same grain bullets with "about" .050 spread between them, good thing that there are lots of 30 cal bullets too chose from.

Base model of 1000 with 10 mpr winds, all from the same range,,, varying +/- conditions on top of that I know.

At least I'll have lots of fire formed brass if I shoot all fall right threw the winter. LOL.

Don

 

[RockyMtnMT]

When it comes to hunting the general rule is there is no replacement for displacement. Larger dia bullets make larger dia holes.

G1 vs G7. Two different drag profiles. The G7 profile looks worse on paper because the number is lower. It does a better job of matching up drops out to long range than the G1 profile on vld type bullets. The G1 profile is for flat based bullets and more traditional semi spitzer type nose profile.

Use the JBM Ballistics calculator and plug in real numbers for cartridges and elevations and temperatures to get an idea of what you will be dealing with. Trust me a guy can wind up spending a lot of time working out different situations deciding what to use.

It sounds like in your posts that you do not hunt at very long range? Under 500y? If this is the case then the bc of different bullets will make very little difference. Better bc bullets start to show their capabilities after 500y and then after 1000y the difference becomes pronounced.

There are lots of gives and takes when it comes to bullet choice. Some guys wind up using two different bullets in one rifle. One for the close encounters and one for long range.

When customers ask me to recommend hunting a bullet, the first thing I ask them is what is their realistic hunting range. From that answer we then start to consider other things.

Enjoy the quest.

Steve

 

[Don A Parsons]

Thanks Steve

I finally found a bit more info on the Web, and like you mention,,, JMB ballistics sight is a wealth of finding out the difference between bullets.

I like the idea of larger bullets, 30 and 338 caliber put it out there at distance, I guess the 270 and 7mm do as well.

I tried the 243/ 6mm bullets years ago on critters and it seemed like they would penetrate thin and thick skin game, but the entry holes were small,,, if the bullet found a tuff area towards the exit side they would get hung up with out punching threw.

Not alot of impact like the bigger bullets.

After reading the Roy Weatherby story I see how this Hyper Shock idea came to be,,, due to the limit bullet selection of the time.

Roy had 3 options.
A- Make a bigger case with more volume and powder to get the limited bullet of that era up to speed. The Hyper Shock idea.
B- Try to make better bullets in those years.
C- Just get by with what was out there.

We all know what Roy did since he was a very skilled re-loader that soon became a very skilled rifle case designer and builder.

I'm sure he even considered making a bullet in his quest, but the Hyper Shock idea might of been the easier path in those years.

The 257 and 270 Weatherby cartrages look like they get it out there since they are clipping along at a pretty good speed.
I'm not suggesting that the big rave of the 6.5 Creedmoor is not a capable cartrage as folks are taking some good size game,,, it is this that brings me to looking at the big picture of why this is,,, and the difference between lager too smaller bullets.

This is what sparks my interests.

The theory in my head tells me that it's wize to have more than enough energy on the thick skin animals,,, that and a fraction more depending on the size of game and distance.
Much like what you mentioned Steve.
This is not forgetting the variables either that was mentioned as well.

BC and SD play roles in game harvest, I'm guessing BC plays its role when the distance gets into the 600 to 1000 meters and beyond.

Tomorrow I'll start with one caliber, looking at it with different BC values at its set muzzle velocities,,, the do the same thing at slower ft-per seconds as it travels down range...

I'm sure it will show signs of variables at different stages to target.

It will be time consuming, but I end up with a pattern of what to expect.

Then the same with a smaller bullet and case on my choosing so I can compare the 2 different size caliber bullets and the cases that send them on their way.

I need to make sure that conditions and hidden variables are matched, or as close as possible between them.

Yes that 1 case and bullet is small as the other might have a larger case and heavier bullet, but that the way it goes.

At least both will be at their max potential for what they are.

5 re-loading books will show me where these 2 cartrages are, then using the JBM calculater will assist me in some ways to what I'm looking for.

Don

 

[barefooter56]

I'm starting this thread too get a better grasp in this area as I begin my journey into long range shooting,,,, "not hunting."

BC things were not part of my game harvests in general, well only part of it let's say. So I'll cut too the first chase.

G1 & G7 I partly under stand, so here's my questions.

G7 differences of let's say .300 and. 315 would make ruffly how much difference over let's say 1000 yards / 900M.

There must be a tool too calculate this.

Next question.
G1 differences of .500 compared too a bullet that has .600BC would be different in what way.

I ask this as I'm doing a F Class build coming up.

There will be more questions too as.

Thanks from Don

Don,
This will help :http://www.bergerbullets.com/a-better-ballistic-coefficient/
and http://www.bergerbullets.com/form-factors-a-useful-analysis-tool/