7.9x57 question for the experts-Ogive/Ballistic Coefficent

These three cartridges are being offered on one of the auction sites. They are listed as “tropical” rounds with WWII headstamps - Patr. S.S.-Trop. (lead ball) -green annulus & mouth band. -Patr. SmK -Trop. (AP) -red annulus & mouth band. -Patr. SmKL’spur -Trop. (APT) -red annulus.

What caught my attention is that the bullets appear to be 10 ogive ( or greater). I didn’t know that 10 ogive bullets were in common use during WW II. Are they correct?

Ray

Unfortunately, I am technically ignorant of how to assign a number to the ogive of a bullet. I can tell you that all of the specimens shown pictured appear to be completely original. Not all German 7.9 Mauser rounds had the identical ogive - Type S ball is quite different from Type s.S, the latter having a “sharper” ogive" and rounds like P.m.K. had a different ogive yet.

Whatever the number of the ogive is on the rounds pictured, to my eye, and I have handled literally thousands of these rounds, appear quite correct.

John

Back when I was shooting long range (1000 yards), being able to judge a bullet’s ogive was almost mandatory if you expected to win anything. It takes some very expensive tools to measure an ogive but after a while it’s possible to make an educated guess just by looking at two, side by side, with a 7 being the standard, more or less…

I did not realize that any military bullets were made with anything greater than a 7, up until 1950 or so. (Except for a few exceptions of course). Bullets greater than 10 did not appear until even later, as far as I knew.

I learn something new every day. Thanks for your input.

Ray

hello Ray
what is the mathematical definition of your number (7, 10, 13) ?
thanks
jp

jp

The number refers to the radius of the ogive in units of the bore diameter. So, for the three shown, a 7 would be 7 x .300 = 2.1" radius. That’s for a simple tangent ogive. Other types of ogives, such as a secant ogive found on many Hornady bullets, is more complicated.

Larger ogives generally mean a higher Ballistic Coefficient (BC) which means greater resistance to wind deflection, less drag, and slower loss of velocity.

Ray

Ray: The original 8 m/m Lebel balle D bullet of 1898 is also of the pointy persuasion, and the German 7.9 m/m boat-tail bullets closely follow the point form of the balle D. Whether they are identical in ogive radius or not I don’t know, but they’re close. Likewise the pretty little .276 Pedersen bullet. Jack

I had Dave Corbin build me a point form die to match the German 7,9 sS profile many years ago. It comes out to a little over 10s. 10.16s or so IIRC. Standard for German 7,9 other than the “S” profile which is used on the 154 grain S ball and the Smk-H (TC-AP). JH

Ray,

What are the head stamps?

Rgds.

It’s fairly simple to calculate the ogive radius, if you can actually measure the cylindrical diameter and the length of the nose, assuming a meplat diameter (usually about 0.1 X the bullet diameter). I probably can’t find it now, as it has been years since I did it, but I made up a spreadsheet to calculate radii in calibers of both secant and tangent ogives from physical measurements. Not too often one must do that, but at the time I had the need.

Well, I learned more about the 7.9mm cartridges in a couple of hours than I will ever need to know.

Dutch - here they are.

Ray

By the way, for those who may wonder but are afraid to ask, the US Cal .30 M1906, M1 and M2 Ball bullets are 7 ogive. The 7.62mm NATO M59, M62, and M80 are 10 ogive.

Ray

While on the subject of nose profiles, for a long time I have observed that there must be slight variances and inconsistencies in commercial bullets, and also military bullets. The reason for this is that there are often seen to be differences in cartridge OAL after reloading. Further, such differences tend to be grouped. For example, one group may have a COAL clustered very close to 3.300", another may be 3.284", and still another may be 3.309", all with exactly the same seating die setting. The only reason I can come up for this is that a typical box of bullets may contain mixed production from several bullet machines each having slight variances in their forming dies from the others. Has anyone else had this experience?

This is not a reloading question, but a bullet nose profile question.

Dennis

As I’m sure you know, one of the differences between Match bullets and ordinary bullets is that the Match bullets have very uniform ogives. Competition shooters have all sorts of gizmos to measure seating depth, not in terms of OAL, but rather in the relationship between the throat of their rifle’s chamber and a datum point on the ogive. OAL, especially with hollow point bullets, means little to them. We (shooters) used to measure and sort Match bullets by ogive measurements, but today’s bullets are so good that it’s a waste of time.

Ordinary bullets will not have that same uniformity and so OAL will vary, even using the same seating die setting. For ordinary hunting or plinking ammunition it doesn’t really matter.

Back when FA and LC were manufacturing National Match, International Match, and Palma Match ammunition, bullets were constantly tested for uniformity and only the best were set aside for match use. The others, though still very good, were loaded in practice ammunition or sold through the old DCM.

Ray

I was not referring to match bullets, just ordinary ones sold for hunting or plinking use. In effect, the seating die punch does describe a datum circle, so it seems that with a constant seating die setting, the differences in OAL would have little to no effect on how far the bullets are spaced off the lands at the end of the chamber. My question was more along the lines of just how consistent are bullet nose profiles from run-of-the-mill bullets from any of the large makers such as Sierra, Speer, Hornady and the various ammunition manufacturers?

By the way, it has occurred to me that by segregating cartridges by close COAL measurement might improve target grouping performance of non-match bullets, i.e., measuring and shooting each COAL group separately, but I have not tested that hypothesis.

You could phone Sierra and ask them. They are good-old-boys and will answer most questions. But, I’d bet that is one that they would decline. They must go through a lot of bullet forming dies in the course of a year and I can’t imagine that they are all exactly the same.

Segregating cartridges by base to ogive measurement would probably produce better results than measureing and segregating by OAL. Meplats will vary so much that OAL wouldn’t mean much. But, try it! Let us know how it turns out.;-) Whenever I try something like that I get fantastic results the first time and think I have hit the lottery. Then on the next group . . .

Ray

Ray, the head stamps are correct.

Rgds
Dutch

Very interesting.

1. Have you the mathematical relations between this number and the ballistic coefficient ?

2. I looked at the different radius for some french ctges and here are some examples:
7.5 Mas Ordinary bullet Mle 1924 : 7.8
7.5 Mas Tracer Mle 1950 7.8
7.5 Mas Mle 1958 : 4.84
7.5 mas Tracer Mle 1959: 6.75
30 Nato French Tracer : 6.54
30-06 French Ordinary bullet Mle 1949 : 6.84
303 : 7.92

Interesting to note the differences between the tracer ctges

JP

JP

Ballistic Coefficient is a product of a bullet’s entire shape, not just the ogive. Some of the features are difficult, if not impossible, to measure, so BCs are often estimated based on known BCs for other bullets with similar form factors. To obtain a true BC, bullets are fired over a given distance between chronographs set far apart to measure the time of flight. Or, more modern methods, such as using Doppler radar to measure a bullet’s performance throughout it’s entire flight. But regardless, real BC can only be measured by actual firing tests.

For most practical applications, such as generating a ballistic table, estimates of BC are sufficient. I would suppose that rockets to the moon or Mars also use estimated BCs, plus a lot of head-scratching. ;-)

One reason that BC is such an important number in ballistics is that two bullets or two projectiles having the same BC, fired at the same velocity, will have the same ballistic characteristics regardless of weight or diameter. That’s one of Mother Nature’s rules and it’s impossible to bend or break it.

ray

Not only the bullet geometry, but also the bullet mass, i.e., sectional density. A wooden bullet of the identical shape and dimensions of a lead bullet will have a far lower BC. There are some analytical methods for estimating BC, but I don’t know how accurate they are. Experimental measurements are far better, and I imagine there are very few bullets that have not had their BCs determined and published somewhere.

Dennis

Back in olden days, before chronographs, BCs could only be estimated using complicated measuring devices and mathamatics. At times, the results were fairly accurate, but often they were not. Quoting the Sierra Bullets ballisticians, “. . . we learned very quickly that BC values for all bullets need to be measured by firing tests; there is no other way to make an accurate determination. . .”

But, I think you’ll find that there are still many bullets that haven’t been measured. Manufacturers usually publish the BCs of their bullets but many of those BCs are only estimations. Estimates are close enough for most uses. But even when you are using a bullet with a tested BC, it’s a good idea to verify a ballistic chart by actual shooting. BCs change with velocity and environmental conditions and there is no way a manufacturer can afford to test all of their bullets under all of those conditions.

Ray