roguetechie said:

Would you happen to have the ff of the 62 grain mk318 mod 1 on hand?

According to Bryan Litz, the Mk318 Mod0 C7 is 0.126 so the i7 is 1.40.

This bullet is closer to a soft point hunting bullet than anything else.

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

stancrist said:

Is there a useful purpose for the "specific energy" comparison?

Well, for a given bullet construction, terminal effects are all linked to the bullet terminal energy.

That's one of the conclusion of the Small Arms Ammunition Configuration (SAAC) Study.

You can design more or less effective bullet structures, but for a given bullet design the one with the more KE will be the more effective.

That's also a conclusion of fielding the M80A1 along the M855A1, the former being able to defeat intermediate barriers at a much longer range than the later.

Even the volume of a bullet cavity in soil (and hence the visual effect of a near miss), is linked to bullet KE.

So, bullets are delivering KE to the target, and soldiers are carrying kilograms of ammo to perform their duty, so dividing kJ of target energy by cartridge weight is a "quick & dirty" indicator of the ammo capability.

You just need to multiply this specific energy with a hit probability to compare the effectiveness of different cartridges.

EmericD said:

Well, for a given bullet construction, terminal effects are all linked to the bullet terminal energy.

That's one of the conclusion of the Small Arms Ammunition Configuration (SAAC) Study.

You can design more or less effective bullet structures, but for a given bullet design the one with the more KE will be the more effective.

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

EmericD said:

So, bullets are delivering KE to the target, and soldiers are carrying kilograms of ammo to perform their duty, so dividing kJ of target energy by cartridge weight is a "quick & dirty" indicator of the ammo capability.

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

And when they shoot, they fire the number of cartridges deemed necessary, not an arbitrary amount of ammo weight.

If the same number of rounds is compared, there is negligible difference in the downrange energy of M855A1 and 7N6.

EmericD said:

You just need to multiply this specific energy with a hit probability to compare the effectiveness of different cartridges.

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

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

gatnerd said:

I think it's just a handy shorthand for measuring both long range effectiveness compared to cartridge weight. I actually like it - easier to grasp at a glance then a series of ballistics charts.

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

Second, it is very misleading because it compares the retained energy of the bullets from one kilogram of cartridges.

Soldiers shoot whatever number of rounds they think is needed, regardless of cartridge weight.

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