The 5.45 has a great shape but is let down by poor energy and light bullets...AK74 never had a very long barrel either.

5.8chinese has about 200ft lbs over 556 but a poor bullet shape.

Instead of neckless i think you are better chambering your ar15 for a 224valkyrie or similar 6mm.....25rnd magazines are a minor drawback.

Frankly the US could have avoided NGSW by converting ARs to a really hot souped up valkyrie round.

On subject of NGSW, what will UK, france and germany do if it gets adopted by US?

smg762 said:

5.8chinese has about 200ft lbs over 556 but a poor bullet shape.

If i7 of 0.95 (DBP10), 0.96 (DBP191) or 0.97 (DVC12) are "poor bullet shape", then what about the 1.18 i7 of the M855A1!

The mighty M855A1 is delivering 280 J at 600 m from a 12.3 g cartridge, that's 23 kJ per kg of ammo.

The 7N6 is delivering 300 J at 600 m from a 10.5 g cartridge, or a specific energy of 29 kJ/kg (+25%).

The 7,62 x 51 mm DM41 is delivering 920 J at this same range from a 24.0 g cartridge, or a specific energy of 38 kJ/kg (+65%).

The DBP10 is delivering 530 J at this same range from a 12.9 g cartridge, or a specific energy of 41 kJ/kg (+75%).

The 6.8 x 51 mm should be close to 1500 J, so even with SIG ~22 g cartridge that's a specific energy of 68 kJ/kg (+200%), and more than 80 kJ/kg (+250%) for Textron or True Velocity.

The new Chinese 5.8 rounds looked really nice to me but that breakdown you just did certainly puts things into perspective.

And oh wow a 1.18 ff for m855a1 is pretty ouch. 

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

Also do you know how much of that .1.18 i7 is down to the EPR gap they had to leave to get reliable terminal effects by chance?

Is there a useful purpose for the "specific energy" comparison?  Because I  sure don't see a logical reason for it.  Nobody shoots a kilogram of ammo into one enemy soldier.

In practice theory is different.

Or

Even parrots can talk, doing is another thing altogether.

Common phrases in Brazil, mine aren't perfect translations but stress your point: until it's proven it's only an idea, no matter how good it seems to be.

I must say that even when proven you can still debate whether the testing was adequate, the world is full of stuff that worked like a charm during testing but failed miserably in the real world (eg the Soviet tank busting dogs).

nincomp said:

The US, in particular has been designing cartridges that do not permit long ogives for decades.

I think probably the best thing to come out 6.5 Creedmoor's meteoric rise to popularity is that broad swathes of the US Consumer and Military market has finally realized the value of long, streamlined bullets and cartridges that allow longer ogive spaces. We're finally seeing an understanding that projectile BC is just as / even more important than the muzzle velocity and energy specs of the cartridge. 

And we're seeing this now with NGSW, where a nice, pretty shapely EPR is being used as the General Purpose projectile.

Could things be better? Of course. But overall things are trending in a positive direction in regards to BC's.

Now if we could just get US bullet manufacturers to abandon using G1 bc's for their rifle bullets...

stancrist said:

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

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. 

In terms of judging future equipment capabilities, I think there is a sliding scale between 'what currently exists' and 'what could exist.' 

I dont think we have to stick strictly with 'what exists' but also think we should be cautious about basing out analysis too far into the 'what could exist' level. 

For example, replacing the current M4A1 carbine:

Exists and Military tested: URG-I upper receiver as used by SOCOM. This thing has a NSN # and we can buy it right now online for testing and analysis. 

Exists in components but not tested, but should work fine: URG-I Upper w/ 416 barrel plus compensator, hydraulic buffer for FA controllability, 40rd mags (My M4A2 concept). All these parts exist now, and said rifle could be assembled 2 weeks from now and tested if any of us had a Class III FFL for testing automatic weapons.

Exists, in experimental form, not sure how well it works: The current NGSW guns and ammo. They all exist, but we're not really sure if all the bugs have been worked out, or how well they really will work. Could go either way. 

Does not exist, but little reason to believe it couldnt be built if $ was enough: An 'AR12' intermediate rifle for a 2.5" COL 6mm HAGAR rifle firing 85gr VLD's based on off the shelf projectile designs. This rifle doesn't exist, but based on the existence of the Six8 LWRCi rifle, as well as some of the hybrid lightweight AR10's that use some ar15 components, theres little reason to think any of the major firearms companies would not be able to build an AR12 if the government had laid out a big $ program to build one (like NGSW for 6mm GPC.) Fundamentally, no new technology needs to be pioneered to make the AR12; likely biggest development hurdle is having Magpul make a 30rd 6mm Hagar mag. 

Does not exists, may or may not work depending on prototype technology: The above AR12 6mm Hagar rifle - but using polymer TV neckless cases at 80kpsi. Now we're entering experimental but as yet not fully proven technology (high pressure cases) plus were talking about creating a brand new rifle design based on firing high pressure, likely requiring a new bolt design and possible other strengthening. 

Does not exist, relies entirely on ambitious simulated future technology: This would be the some of the 4-5lb FEA designed rifles firing high pressure cartridges with ultra low drag projectiles. These would be totally awesome and best choice if they did exist, but its also the weapon we have the least proof to rely on that its actually possible. 

Does not exist, sci-fi: We need to replace the M4 with a PDW firing caseless neurotoxic flechettes. Here we're relying essentially on something cool from Neuromancer. 

Personally, I lean towards the more conservative side for designs. A weapon doesn't have to exist, but for me they need to be grounded in what does exist and have a high probability of working. 

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