Are Hornady's BC figures overly optimistic or accurate?

Really depends on the bullet. I have used a bunch of them and in general the BC value is ok. However, the G function varies a whole lot.

My testing of the 162gr Amax 7mm works out in two rifles to follow the 0.625 BC but a drag function of G7. Yes Martha, thems bullets fly goofy good.

With a 3150fps, its takes 17.5mins to go 100 to 940yds from my Savage. Ranged by a Leica 800 rangefinder. chorny chronograph. Do the math on that one. You can assume a 10% equipment error if that makes you sleep better. Still the numbers will come out goofy good.

The other bullets that fly really well are the 140gr SST 6.5, 155gr Amax 165gr SST and IB in 30cal. The 162gr SST in7mm is pretty good too but not as good as the amax.

Very good but not in the same league as above is the 270 150gr SST. Still way better then anything similar but works out to a G5 curve. Most BTHP use a G5 or lower drag function.

What that means is it would take a way higher BC/low G function to equal a lower BC/high G function bullet. Just play on JBM software and you will get the idea really fast.

Using the G5 function, these 162gr Amax would need a BC WAAAAAYYYY higher then 0.625 as they fly from two of my rifles. I have talked to Hornady on this topic a number of times and they just shrug their shoulders. They prefer to understate their bullets performance.

I wish someday bullet manf will standardize how they calc their BC. It is very misleading.

Jerry
 
Absolutely simply because some bullets don't shoot well in some rifles. Also, how a bullet is engraved/damaged during the trip down the barrel will change its BC in flight.

There is only one way to find out...However, starting with a bullet with good creditials doesn't hurt.

Jerry
 
Jerry, you can't say the BC value is OK but the G function varies. The companies publish G1 BCs, they are either good or not. They don't say here's a BC pick a G function.
The truth is all the companies claim as high a BC as they can. When someone like Henry Childs tests them they usually gets close to the published value or slightly less. The problem with your results is that BC values are very sensitive to all the data (velocities, drops etc) and unless you really have appropriate equipment for testing BC, then all you can determine are the scope adjustments that you need for your system. By all means use the drops you record, but you aren't measuring BC. That is why the company shrugs its shoulders, because they have done at least some accurate testing, and they know they can't reproduce the BCs you measure.

In my rifles, using published BC values usually gets me within a couple of clicks at 1000 yards.
 
In fact I can say that a BC value is related to the G drag function. Here is a link that shows you the number of drag functions used for small arm ballistics (I am sure there are more). There is better list with more info but can't find the link.

http://www.snipercountry.com/ballistics/

It's just a bit down the page. As you see, each G function relates to a family of bullets based on profile and design. The vast majority of BTHP match bullets as typified by Sierra MK are G5 in design. Reg hunting bullets use a different function. The few but growing number of true VLD bullets are G7. Several Hornady poly tipped bullets, like the 162gr Amax, fall into the VLD shape and G7 drag function.

Each G function has its own math algorithm as it relates to a ballistic program. They affect results quite dramatically. A higher number does not mean a better number. Just a different class of bullets.

The vast majority of bullet manufacturers do not test their bullets to determine a BC. Many, including some match bullet makers, get their values from the companies that make their bullet forming dies. The die makers usually use a form program to generate a BC. Sierra is one of the few that fires their bullets and derives their BC by time of flight/velocity analysis. If you know of others, list them.

However, no one ever refers to a G function when they list a BC. I guess they assume we know or don't care. That is why some bullets are way off their printed values under real world shooting. The Sierra data is usually quite accurate.

There is a trend in custom LR bullets to work on a 10 ogive bullet shape. A few are taking the lead from Hornady and using a Secant Ogive shape instead of the more common Tangent ogive. A nip here and a tuck there and voila, some pretty impressive bullets. Rebated BT are also being played with and some very nice results are coming back, but is that bullet shape or just quality manufacture?????

I have switched almost completely from HP match bullets because tests several years back showed that poly tipped bullets shot way flatter. These tests compared the then new Nosler J4 308 168gr, Nosler BT 165gr, Hornady BTSP and SST.

All shot from the same rifle and same muzzle velocity. All tested at 100yds for same POI. Testing at ranges from 600yds to 850yds showed that the good old BTSP isn't so aero (no surprise there), the next was the J4, then a close tie between the BT and SST (the SST won in my case). The difference on come ups was up to 4 min. That's an enormous difference.

I have also compared data with a variety of LR shooters. Assuming that we are all dealing with proper procedure to measure our comeups, ranging, and velocity, the poly tipped bullets fly better in most instances (given the same calibre and bullet weight). This covers several calibres and cartridges. This data is available on sites like Longrangehunting.com, BRcentral.com, etc. You just need to search for posted results.

Many have doubted these results. In all instances, they have never fired any of these bullets. I am not saying that poly tipped is the only way to fly. Of course not, because the rest of the bullet may be a horrid shape. however, most bullet manf. that use poly tips are also doing a pretty good job with the rest of the bullet.

I have challenged several doubters to do any type of shooting tests they wanted. A few took me up on it and they found the same thing I did out to 1000m. Some even got similar goofy results.

Every rifle is different and not all bullets shoot in all barrels. However, the poly tipped bullets can offer several advantages over HP bullets. You don't have to worry about meplat uniforming, the tip is the 'same' shape and profile, they do provide lower drag (at least at the tip), Hornady who makes most of the poly tipped bullets today also uses a secant ogive profile and a pretty agressive one in the Amax line.

You will read that I include the term 'goofy' results in my posts. I don't have the technical equipment to do a bona fide BC calc. however, I can infer the results by using my data through shooting and what ballistic programs spit out. Even with a dash of error, the results are impressive.

Try some, you might be as impressed as the many others now shooting the Amax and SST and Interbond. If you shoot a 6.5, try the 140gr SST. The 6.5 Amax is good but the SST is better. The old Amax was in a league all its own but has since been changed. Bummer...

For the 308 shooter, the 155gr Amax can lead to some very impressive LR results that exceed those from the 175gr MK. The 162gr Amax in 7mm is simply superb with the SST not far behind. The 165gr 30 cal SST will go way out there and stays stable even after going subsonic. The 165gr IB has an even higher BC based on shape and come ups (too expensive for volume shooting and the difference is not huge). I know a few shooters using the 178gr Amax with superb accuracy and trajectory. And on it goes...

Try some. What is the worse that will happen????
Jerry
 
Yeah I know all that. The most appropriate G function will depend on the bullet design. Bullet manufacturers quote G1 BCs whether they are the most appropriate or not because they look the highest and are what most people are used to hearing. The fact that they need to use 3 or more G1 BCs in different velocity ranges shows that they should be using a different G function. When they quote a BC though, they are quoting G1.
The best G function to use may vary, but the one that the manufacturers use doesn't. You can't keep the G1 BC and switch G functions.
 
I did this because real world shooting of so many bullets just didn't agree. That is when I started to research the G function. After inserting the right function, data started to agree with real world experience. Kind of struck me as bizarre that the printed BC worked when the 'correct' G function was used.

That is what lead me to speculate that some are simply printing the BC value but missing out the G function. Others simply using WAG numbers or ones making their product sound better then they really are.

If all bullet manf's used G1 functions in the printed numbers, the BC values of some bullets would be way higher then the printed numbers now used. Hornady would have stupidly high numbers in certain bullets. One company that doesn't 'chase' the numbers - bizarre but that is what the techs have told me.

Yes, they get calls like mine going WTF is going on with those printed BC values???? Why so low????

Jerry
 
You must log in or register to reply here.
Back
Top Bottom