stancrist said:

First, it tells nothing about effectiveness, which depends more on bullet configuration and construction, than energy.

Well Emeric had qualified that as 'for a given bullet construction.' 

Its less relevant for comparing these very different bullets from different countries (m855a1 vs 7n6 etc).

But it could be a handy metric for comparing a suite of cartridges based around a common projectile design and shape. For example, say Nathaniels suite of Romulan/Vulcan cartridges, all designed around an EPR bullet of identical form factor, just scaled to different calibers (5mm to 7mm):

https://www.thefirearmblog.com/blog/2017/09/09/romulan-vulcan-preference-driven-vs-process-driven-design-field-small-arms-ammunition/

Here the 600m energy per kg metric would provide a decent guide.

However, I personally am not an energy guy when it comes to EPR; I think fragmentation range is the more important metric. IE 'distance to 1700fps' or whatever the exact frag velocity is. The rationale being that a fragmenting EPR hitting with 300 ft/lbs of energy at 600m is superior to a non-fragmenting EPR striking with 500 ft'lbs of energy at 600m. 

Although come to think of it, I dont know how impact energy effects EPR fragmentation velocity? That would be a wrinkle if a 62gr EPR needs 1700fps/398 ftlbs to fragment, but a 135gr 6mm only required 1300fps because it was still striking with 500ft'lbs of impact energy. 

stancrist said:

Granted, but you compared cartridges that have bullets of different configurations and construction.  IMO, that alone makes the comparison of questionable value.

The initial comment was about the "poor" form factor of the Chinese 5.8 mm or the "lightness" of the 7N6 bullet.

The reality is that those 2 rounds are delivering more energy at 600 m than the 5.56 mm, for a given soldier load.

I agree that the bullet design of those 3 rounds is not the same, but it's probably easier to design an EPR-like bullet for the 5.45 x 39 mm or the 5.8 x 42 mm, than a bullet with a long ogive and low FF for the 5.56 mm...

stancrist said:

The trouble is, soldiers do not carry a specified weight of ammo.  They carry a specified number of rounds of ammo.

And this number of rounds have a certain weight & volume, so if you want to avoid an "apple to orange" comparison, you need to compare a system weight. That's the basis of the 1952 "Hall" report, or the later SAWS study.

If the same number of rounds is compared, then the 5.56 mm will not shine when compared against the 7.62 mm.

stancrist said:

Disagree.  First, effectiveness depends as much on bullet configuration and construction, as on impact energy,

That's right, but it's much easier to change bullet construction (like the M193 / SS-109 / M855A1) than to significantly improve impact energy after designing a cartridge.

Even more so if you want to compare different cartridge design or ballistic solutions.

stancrist said:

Second, using a purely arbitrary (1.0 kg) weight of ammo produces a completely unrealistic ammo comparison.

I have to disagree. Dividing downrange energy with cartridge weight is giving you an "intensive" parameter, so you know what's your weight penalty for the energy delivered to the target. It's not the same thing as trying to evaluate the performance of a soldier carrying 80 rounds of 5.56 mm.

gatnerd said:

stancrist said: First, it tells nothing about effectiveness, which depends more on bullet configuration and construction, than energy.

Well Emeric had qualified that as 'for a given bullet construction.' 

Not in his initial post on the subject, which is what you and I were discussing.

gatnerd said:

Its less relevant for comparing these very different bullets from different countries (m855a1 vs 7n6 etc).

But it could be a handy metric for comparing a suite of cartridges based around a common projectile design and shape. For example, say Nathaniels suite of Romulan/Vulcan cartridges, all designed around an EPR bullet of identical form factor, just scaled to different calibers (5mm to 7mm):

Here the 600m energy per kg metric would provide a decent guide.

How would it provide a "decent guide" and to what?  And why 600 meters?  That seems like an arbitrary figure.  Why not 300?  Or 900?

I honestly do not how energy per kilogram of ammo weight gives any useful info. 

gatnerd said:

However, I personally am not an energy guy when it comes to EPR; I think fragmentation range is the more important metric. IE 'distance to 1700fps' or whatever the exact frag velocity is. The rationale being that a fragmenting EPR hitting with 300 ft/lbs of energy at 600m is superior to a non-fragmenting EPR striking with 500 ft'lbs of energy at 600m. 

Now you're contradicting yourself.  First you said that the energy per kilogram is a good basis for comparing Nat's theoretical EPR cartridges, but now you say that metric does not apply to EPR.  

gatnerd said:

Although come to think of it, I dont know how impact energy effects EPR fragmentation velocity? That would be a wrinkle if a 62gr EPR needs 1700fps/398 ftlbs to fragment, but a 135gr 6mm only required 1300fps because it was still striking with 500ft'lbs of impact energy.

I've never seen an impact energy threshold for bullet fragmentation, only impact velocity. 

And IIRC, aren't there YouTube videos of 5.56 and 7.62 EPR fragmentation threshold tests?

Gr1ff1th said:

That is a hilariously bad form factor, even for a 5.56 bullet 

If you think that is bad, please don't look up M80A1!

Oof lol, we thanks for the answer.

There's some m856a1 kicking around Ive thought about picking up and loading just for fun.

Since it looks like my choices are crap or crap it can't hurt lol

Edit: Post deleted as being late to the show. I had overlooked the above discussion.

stancrist said:

Assuming 210 rounds for both Chinese and Russian riflemen, the total energy @ 600 meters is almost identical for all three calibers.

That's an hypothesis easy to challenge, as the M855A1 is delivering ~338 J at 600 m from a M16A2 and the DBP10 is delivering 536 J.

That's nearly 60% more energy than the 5.56 mm when fired from the M16.

For 210 rounds, that's 71 kJ for the M16 vs. 112.5 kJ for the Chinese round, for a weight penalty of 126 g, or... wait... 71 kJ / 2.583 kg = 27.5 kJ/kg versus 112.5 kJ / 2.709 = 41.5 kJ/kg.

stancrist said:

1.  You are not dividing downrange energy by cartridge weight (12.3 grams, for 5.56mm).  You are postulating an arbitrary weight (1.0 kilograms), and proceeding from there to calculate a total energy on target that is grossly distorted from reality.

Hum... no.

stancrist said:

2.  Since each of the three rounds delivers roughly the same energy @ 600 meters, the ammo weight penalty is simply the difference in weight of 210 cartridges in each caliber.  The 5.8mm has the greatest weight penalty, with 210 rounds weighing 126 grams more than an equal number of 5.56mm rounds.

Hum... no² (see above).

stancrist said:

In that case, your comparison is even more badly flawed than I previously noted.  Not only did you compare just a fraction of the system ammo weight, you entirely omitted the weight of most of the system: The rifle and magazines.

Is there something that make you think that there are physical laws that will make a 5.56 mm rifle absolutely different from a 5.45 or 5.8 mm?

I mean, in the case of a 5.56 mm NATO vs. 7.62 mm NATO, the rounds length and rifle action length are not the same, but for the 5.54 / 5.56 mm / 5.8 mm all those 3 rounds are built on the same action length.

EmericD said:

stancrist said: Assuming 210 rounds for both Chinese and Russian riflemen, the total energy @ 600 meters is almost identical for all three calibers.

That's an hypothesis easy to challenge, as the M855A1 is delivering ~338 J at 600 m from a M16A2 and the DBP10 is delivering 536 J. That's nearly 60% more energy than the 5.56 mm when fired from the M16.

Right.  I really screwed up there.  Clearly, I stayed up far too late last night/early this morning.  I think I need to go to bed much earlier tonight...

EmericD said:

stancrist said: In that case, your comparison is even more badly flawed than I previously noted.  Not only did you compare just a fraction of the system ammo weight, you entirely omitted the weight of most of the system: The rifle and magazines.

Is there something that make you think that there are physical laws that will make a 5.56 mm rifle absolutely different from a 5.45 or 5.8 mm?

Do the 5.56mm M4, the 5.45mm AK74, and the QBZ191 all weigh the same?  Do their magazines all weigh the same?

EmericD said:

I mean, in the case of a 5.56 mm NATO vs. 7.62 mm NATO, the rounds length and rifle action length are not the same, but for the 5.54 / 5.56 mm / 5.8 mm all those 3 rounds are built on the same action length.

Hmm.  I'd think that the 5.8mm would require a somewhat longer action.

Not really, the bullet in that photo was manipulated. The 5.8mm bullet was obviously pulled out, and it was inserted crooked even when it was reinserted. The correct data of the real 5.8x42mm bullet is here.