Ballistic Coefficient Exaggerated

[RAG]

I'm curious how many people have found for themselves that the G1 BC supplied by most bullet companies are of little use for calculated drop ballistics, largely in part to their being exaggerated (for sale purposes I'm sure). Of course, it's difficult too because the G1 BC generally drops off as velocity drops, so saying a bullet has a .25 BC doesn't help much if that BC is only realized over 3800FPS, which could easily be .20 at 1000fps less. The only company I think is relatively honest is Sierra...using their figures and applying it to the equivalent weight/style of bullet of other companies puts my ballistic software data pretty close.

I recently sighted in at 100 yards and then measured the drop a 300, 400 and 500 yards,with light weight varmint ballistic tip bullets (primarily v-max). To get my Strelok ballistic software to match up with the actual drop I experienced, I had to back the BC down to .19 to .21 on most of these bullets...most of which has a listed BC ranging from .25 to .275.

Anyways, just my findings.

 

[Nomad47]

To get Strelok to agree with JBM Ballistics where I use the G7 BC, I find I have to fudge the barometric pressure to get Strelok to be close.

 

[CatShooter]

I'm not so sure that the companies have bad motives in rating their bullets, id est, faking BC's to get sales.

All the companies use different methods to garner their BC data.

There are no standards to assigning BC to a bullet.

Sierra has software that is somewhat convoluted, but each bullet is tested over many velocity ranges, and adjusted to match their own software - and it works well.

But their BC may not work well in another program, or some other bullet might not work well in the Sierra program.

The 55gr SBK has a lower BC than the Hornady 53 V-Max, but if you shoot them at 400 yds for drop, the 55 SBK drops less. It is because the two companies use different methods to derive their respective BCs.

Our bullet companies are pretty honest, unlike most other industries.

 

[KevinThomas]

I've mentioned this before, but I guess it does bear repeating. The multiple BCs used by Sierra are an attempt to force-fit what they recognize is an improper drag model (the G1, which has been the de-facto industry standard since Lowrey developed them), into a more accurate trajectory path that will more accurately reflect the flight path of the bullet, real world.

Bryan and Berger have attempted to drag the industry (kicking and screaming, I might add) into the more appropriate (for their bullets, anyway) G7 drag model. Bryan does the actual firing tests with these bullets to assign BC numbers, and no, I don't believe they're inflated in any way, for sales and marketing purposes or otherwise. What advantage can a company get if their BC numbers are routinely shown to be overinflated hype? None, but a hell of a backlash if that became public. What you're seeing is accurate numbers based on what firing was done. Not saying there aren't mistakes made, and trust me, there are. But the whole process is much, much better than it was 20-30 years ago. Back then, very few people had any concept of what BC was, much less how to use it. Many of the BCs shown back then were the result of estimates, comparative guesses and very rough form comparisons, including the use of Coxe-Bugless tables! Good luck finding too many shooters today who even know what these are, and yes, I still have a complete set, but purely for historical interest.

I'm sure that there are some makers that are using less than ideal methods, but I'll accept that most are good-faith attempts to render a valid BC for their customers. May not always be as close as they might, but most do pretty well. Add into that the errors that most handloaders themselves will make when trying to "verify" the factory numbers, and you'll get a feeling for just how many points for errors there are in this whole program. If you don't have accurate data for correcting the (your) derived BCs back to standard for an accurate comparison, don't be surprised if there's significant errors in the end results.

Lapua uses Doppler Radar firings to determine our BCs, and we are now offering both G1 and G7 models. We're one of the very few commercial makers in the world who have access to this means of testing BC, due to the cost of the equipment required. The figures are good. Used with correct adjustments for your local firing conditions, the results should be spot on.

 

[barnesuser28]

I checked out the coxe-bugless tables and they are pretty darn cool! Also, Barnes tests their BC's using dopplar radar, other than them and Lapua i dont think anyone else does.

 

[KevinThomas]

Sierra's done a couple in the past, but I don't believe they've had access to the radar equipment in several years. We used to have an "in" at Yuma Proving Ground (YPG) who used to get us access in conjunction with a west coast AFTE group. Everyone would do whatever tests they needed, and the results shared among the group for future reference should it become germane. Neat stuff, but I don't think they've done it for many years now.

 

[barnesuser28]

I would have to check to make sure but i believe Bryan Litz referred to some testing done at the YPG in his book: Applied Ballistics for long range shooting.

 

[RAG]

All good replies.

But I guess, this is exactly what I was saying...you'll see one company's 50gr BT report a higher BC than another's 55, both boat tails and of "similar" configuration. Maybe it's not the case, but I always thought BCs help sell bullets and thus some companies "stretch" their numbers some.

I'm not so sure that the companies have bad motives in rating their bullets, id est, faking BC's to get sales.

All the companies use different methods to garner their BC data.

There are no standards to assigning BC to a bullet.

Sierra has software that is somewhat convoluted, but each bullet is tested over many velocity ranges, and adjusted to match their own software - and it works well.

But their BC may not work well in another program, or some other bullet might not work well in the Sierra program.

The 55gr SBK has a lower BC than the Hornady 53 V-Max, but if you shoot them at 400 yds for drop, the 55 SBK drops less. It is because the two companies use different methods to derive their respective BCs.

Our bullet companies are pretty honest, unlike most other industries.

 

[RAG]

Petty much what I was thinking. Thanks for the great info.

I've mentioned this before, but I guess it does bear repeating. The multiple BCs used by Sierra are an attempt to force-fit what they recognize is an improper drag model (the G1, which has been the de-facto industry standard since Lowrey developed them), into a more accurate trajectory path that will more accurately reflect the flight path of the bullet, real world.

 

[chevytruck_83]

if you really want to understand exactly what's going on get brian Blitzer,s book applied ballistics for long range shooting. not only does he explain the methods to find bc but he has more accurate bc results for a lot of popular bullets. keep in mind. once you start using a Chronograph you see how much each bullet varies in speed then the next. so there are a lot of other variables that will effect trajectory.

 

[Norseman]

I believe Jenson bullets was one of the first to promote accurate BC values using the Dopplar Radar Method, matter of fact, he promoted it like 20 year's ago! I wish every bullet maker would use Dopplar Radar Methods.

 

[Raythemanroe]

Using Gseven's load validation, my sierra's 115g bullets got a slight bump in BC! The actual data given and impact points actually came to thirty fps slower and a slight bump in bc

 

[DRNewcomb]

Lapua uses Doppler Radar firings to determine our BCs, and we are now offering both G1 and G7 models. We're one of the very few commercial makers in the world who have access to this means of testing BC, due to the cost of the equipment required.

I imagine that the big advantage of Doppler Radar is that the continuous velocity function it produces allows the bullet to be fitted to the best B.C. model. You can also observe actual behavior at the super/subsonic transition.

Looking at the advance of electronics available to the shooter (e.g. MagnetoSpeed chronograph, handheld laser range finders, etc.) I wonder if we may someday see a Doppler Radar/Laser bullet speed system priced within the reach of the shooting enthusiast?

 

[brian427cobra]

Before dismissing the stated BC, G1 or G7, all other variables must be known, NOT GUESSED, I shoot through a chronograph as much as I can, I always have my Kestrel 4000 up and running, and I log my shots in a logbook, and lets face it, iStelok is not the best ballistic program.