G1vs g7 bc ????

[lionhunter]

In the past month ballistic calculations have been a huge topic of conversation between my hunting buddies and myself!!! I have worked up several different loads, researched many different bullet options, set up a mark 4 8.5x25 on my go to rifle and advised a friend on setting up his rifle for a sheep hunt...

At any rate, we noticed that different ballistic comp programs would spit out different wind and and drop data when given the same inputs. After hours of research and problem solving it comes down to barametric pressure and bc being calculated in different ways...

Word to the wise for those of you calculating your drops..... Be posssitive about how your bullet manufacture calculates the bc on your bullet ( g1 or g7), be sure that the program you use it set to the same bc, and make sure that the barametric pressure is measured in the same way from where you are abstaining your info and the program you enter it into!

It will make a difference!

 

That being said....... I am 90% sure that nosler lists their bc in g7 measurements, but I want to be sure. Can anyone verify this???

Thanks

Whitey

[firstcoueswas80]

nosler Lists G1

[DesertBull]

A typical G1 BC will be in the .500-.600 range

A typical G7 number will be in the .200-.300 range.

 

Hornady SST 162 grain .284 - .550 G1

.268 G7

[STOMP442]

The g7 form factor fits better with most modern day long range bullets having a boat tail and longer ogive. If you know the g7 it will produce a more accurate drop chart as it is not nearly as velocity dependant as a G1. Nosler lists a G1 based b.c. and is generally exaggerated by quite a bit. A quick easy way to estimate G7 b.c. is to take the weight of a bullet divided by 7000 to get its weight in pounds. Then divide that number by the dia of the bullet squared and then divide that number by the bullets form factor. The standard g7 form factor is 1 but some bullets depending on what you are shooting like bergers and Amax have a slightly lower drag profile than the standard in certain calibers so I like to use 0.95 when I am unsure. This will give you the G7 b.c or at least pretty close to it. To find the G1 you simply divide the G7 by .512

For example I will use the sierra 155gr match king in 308 which I know is almost identical to the g7 standard. It has a published G1 b.c of .450

155/7000 = .02214
.02214 / .308×2 = .233 (G7)
.233/.512 = .455 (G1)

As you can see this comes out pretty dang close to the published .450 bc

You can do this for most bullets to find a pretty close estimate in actual b.c. the trickiest part about it is the form factor. All of this data as well as the form factors for most long range bullets can be found in Bryan litz book applied ballistics for long range shooting. Outstanding resource of information and well worth the 50 bucks.

[willhunt4coues]

Applied Ballistics is the best if you have the extra cash get the book, DVD set, and the program for your phone. They do also make a Kestrel that has the built in AB program but don't know how well it works. Again anything related to AB and Bryan Litz will be the key to little tricks and treats to accomplishing long range.

[rcdinaz]

Stomp that is good enough to be a sticky.

 

Could add brief description on a few other items BC, SD, Energy, Coriolis, Spin drift, barometric pressure, humidity, etc...

 

All the potential factors to calculate POI in one place would be great

 

I found turning off spin drift on my hadheld program had a pretty significant impact (in a bad way) on long range accuracy. I believe the quick math you can do in your head was 1MOA for most cartridges on average in the direction of the barrels twist.

[308Nut]

As stomp mentioned, G7 values are less sensitive to velocity variances. This eliminates the need to enter multiple BCs throughout the distance range. Sierra publishes a variety of BCs based on different velocities and this is why many software apps have options to enter multiple BCs. This is valuable when using the G1 model. OR you can use the G7.

 

Personally I find that when using higher BC bullets such as the 30 cal 190 VLD and higher at average velocities, G1 versus G7 is a fairly close trajectory match assuming you started out with good data to begin with. With lower BC bullets, I find that either G7 or G1 using multiple BCs over the velocity range works the best. All of this is with equal to or less than 1000 yards. Beyond that, what I'm preaching here changes.

 

I also find that when converting from G1 to G7 that a .496 multiplier is a closer match than the standard .512 multiplier. For example, converting the widely accepted Litz BC value for the 208 Amax to G7, the multiplier .496 gives a better real world G7 BC than the .512 multiplier. This gives you a .314 which IMHO is more accurate than the .324 G7 BC commonly used. Right or wrong, applying this to the 140 VLD 264 caliber and 190 VLD 30 cal. has been deadly accurate. Comparing these against any decent app will confirm this methodology. Not to be confused with the formulas stomp referenced but solely converting from a proven G1 BC to G7.

 

As far as inconsistency between programs, it is often times subtle differences as whether or not the engine uses 29.53 in. Hg. versus 29.92 in. Hg. as a baseline reference for barometric pressure. Other times its confusion regarding the relationship between altitude and pressure. Often users will enter 6300' and 24.32 in. Hg. when it should be 0' and 24.32 in. Hg. Or 29.92 (or 29.53 depending on the engine) or the actual corrected sea level pressure at location and then 6300' elevation. Some software is more clear and dummy proof than others. More often than not, major differences in results between reputable apps is an operator error but there is almost always some minor differences.

 

M

[308Nut]

Forgot to check the follow topic box.

[STOMP442]

Yeah litz mentions that the .512 number is not a constant but works most of the time on most bullets. The other important thing to input is the scope height. I see a lot of people just keep the standard 1.5" and call it good. Scope height makes a big difference in the calculations.

[STOMP442]

I also have to stress that as great and wonderful as technology is nothing beats real world experience, data and a log book. These programs will get you close and will definitely get you on the gong at long ranges but is rarely centered up. Small adjustments up or down by a click or two are needed to fine tune in most cases.

[308Nut]

/>I also have to stress that as great and wonderful as technology is nothing beats real world experience, data and a log book. These programs will get you close and will definitely get you on the gong at long ranges but is rarely centered up. Small adjustments up or down by a click or two are needed to fine tune in most cases.

And that's part of the fun!!

 

Usually, when the computer doesn't match the real world it's usually one of 3 things or a combination of the 3. Assuming your air density is right, scope height, starting zero, distance, etc... Is all spot on, it's errors in BC, velocity or scope click values that are not right. But as stomp mentioned, it's actual shooting that reveals these things.

[TwoGuns]

This thread reminds me why I shoot a bow....my head is spinning.

[rcdinaz]

Bow is no better!

 

Inclination, fletching twist/offset, site cant, 3rd axis, arrow wt, spine, and a bunch of crap other I haven't figured out.... I know guys that make fishing so technical its scary and funny.

 

 

Like most things it only starts to seem simple after you do stuff a bunch of times as was stated above.

 

My buddies who dont enjoy the learning part and challenge drive me nuts. "Okay you do it and figure it out and show me how"

[308Nut]

Everything is simple until you want to take it to the limits. You certainly don't need 3rd axis sights on a bow and a level and a stabilizer and arrows spined for optimum forgiveness etc.... If you intend on shooting on level ground at 10-20 yards while being happy with hitting an 8" pie tin.

 

It's when you decide that you want to hit a target the size of a softball at 80 yards in every possible condition that complicates things. Then you need laser rangefinders, angle compensation, 3rd axis sights, levels, stabilizers, understanding proper spine, FOC balance, tuning, repeatable form, mental focus, muscle memory etc...honestly archery is just as bad if you own a complicated mind and demand precision shot placement at ranges most archers think is unacceptable. Only....there are no bi-pods and prone positions to be had in archery. Only mind games with your body.

[lionhunter]

Thanks for all the info guys!!! I think I am going to sell on my long range rifles and go back to a 30-30 open sight!!!!!