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For Your Amusement   General Army topics

Started 15/9/21 by stancrist; 14514 views.
stancrist

From: stancrist

9-Aug

Pretty much everyone in this forum has been using ballistics tables calculated using BC, but nobody has ever claimed that such tables were useless and radar data was needed for comparisons.

I do not understand your insistence that radar data is needed to compare ballistics of a 130-year-old cartridge, rather than just generating tables as we have done before using the published BC.  

Hornady Bullets 6.5mm Carcano (267 Diameter) 160 Grain Round Nose

stancrist

From: stancrist

9-Aug

Thanks Tony.  Appreciated.

Farmplinker

From: Farmplinker

9-Aug

Instead of .264, Italian 6.5 is .268 diameter.

EmericD

From: EmericD

9-Aug

There was also the excellent .256 Newton cartridge that predates the "Pig Board Test" by ~10 years, so maybe the inspiration was there.

https://en.wikipedia.org/wiki/.256_Newton

JPeelen

From: JPeelen

9-Aug

"Nobody has ever claimed...", because the large majority prefers to use published BCs and range tables and is not really interested in the physics behind it.    

That is fine with me. But when, as in this thread, cartridges are discussed on technical detail level, we should do it on a sound technical basis. Any comparison on the basis of 130 year-old-data is misleading, because the data is known to be wrong.  

I for my part do not understand your insistence on a computing method that has been dropped by militaries decades ago because of its faults.  

               

nincomp

From: nincomp

9-Aug

Walter00 said:

Hmmm. Wikipedia shows SAAMI spec bullet diameter as .2780 ± .0030 in.

Although that is true, the bullet industry has standardized on 0.277.  This was brought to light earlier this year when some ammo for the 6.8 SPC with bullets within the 0.278" SAAMI spec but larger than 0.277  showed overpressure signs on some rifles.  As it turns out, the SAAMI standards are not always followed, nor should they be.  It surprised me that the SAAMI dimensions are so loose that with many cartridges, a max-specification case will not fit into a minimum-specification chamber.  A few cartridges, like the Weatherby Magnum cartridges are more specific about tolerances, but most are not.

nincomp

From: nincomp

9-Aug

17thfabn said:

The horror, to be caught conflating!!

I got caught conflating once when I was younger, but I am in a healthier place now and am ashamed of my past.flushedgrin

stancrist

From: stancrist

9-Aug

JPeelen said:

...when, as in this thread, cartridges are discussed on technical detail level, we should do it on a sound technical basis. Any comparison on the basis of 130 year-old-data is misleading, because the data is known to be wrong.  

???  I never said anything about using data from 130 years ago.  I said to generate ballistics tables using currently published ballistic coefficients.

JPeelen said:

I for my part do not understand your insistence on a computing method that has been dropped by militaries decades ago because of its faults.

Do we have radar data for cartridges like 6.5 Carcano?  No.  Is it likely we ever will?  No.  The best we can get now are computer-generated tables.

If you want to compare the trajectory and wind drift of different rounds, what is wrong with using data from calculators like this for comparisons?

stancrist

From: stancrist

9-Aug

nincomp said:

I got caught conflating once when I was younger, but I am in a healthier place now and am ashamed of my past.

I think I read that conflatulence is a medical condition.  wink

EmericD

From: EmericD

10-Aug

Hi Jochem,

While I do not have a drag curve for the 6.5 carcano round nose, I have this curve for the very similar 7x64 mm round nose

The corresponding form factor is 0.80 for G1 (between Mach 2.5 and Mach 1.3), and 1.59 for G7 with the obvious limitation shown on the graph (no form factor could reproduce the subsonic behavior of the bullet.

I would say that one reason that the italian army was not really in a hurry to field a spitzer version of the 6.5 mm carcano was that the C7 of the 162 gr bullet was higher than 0.20 in the supersonic domain, which was already similar to the "7.9 mm Patrone S", ".30 Mle1906" or "7.62 mm M80" spitzers.

Switching to a lighter spitzer bullet would have allowed for an increase in MV, only if the Italian were able to have access to the proper powder type (something I don't know).

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