Depending on the resultant ballistics, the cartridge when fired from 14.5" barrels could potentially meet the specific energy threshold of 7.62 NATO at 1,000m if very fine projectiles are used.

Why change the goal post from total retained energy to specific retained energy? 

H_Minus said...

 

Depending on the resultant ballistics, the cartridge when fired from 14.5" barrels could potentially meet the specific energy threshold of 7.62 NATO at 1,000m if very fine projectiles are used.

Why change the goal post from total retained energy to specific retained energy? 

 

It's one of several standard ballistic metrics by which I evaluate different cartridge designs. I typically look at drop at 500m with a 25m zero and 2.6" sight height (considering changing either the zero or the range), maximum range of retention of 2,000 ft/s velocity, energy at 500m, maximum supersonic range, energy at 1,000m, and specific energy at 1,000m, but sometimes I throw in other metrics, and often for smaller calibers that already meet or exceed the absolute energy figure at a kilometer, I drop specific energy because I know the answer is "higher than 7.62mm".

compost2 said...

...the capability for an infantry platoon/patrol to apply or obtain prompt long-range fire is almost indispensable at any time of day, and in the dark and even at night.

They already have that capability, in the form of 7.62mm machine guns and DMRs.

compost2 said...

Am surprised Carniflex or Kirk hasn’t had a go at you already.

Well, Kirk got pissed off at me a couple years ago, and put me on "ignore."   ;^)

As for Carni, who knows.  Maybe he's on vacation?  I haven't noticed him here for a few days.

Pleased to see you put 7.62 MGs and DMRs together. Believe they need to share a round just a bit heavier than .308, also that platoon needs ready access to its own 60mm short barrel mortar. Expect am yet again preaching to another believer.

stancrist said...

autogun said...

...bearing in mind that MGs are always likely to have longer barrels than IWs...

Two words that should never be used -- "never" and "always"   ;^)

Basic English comprehension: "always likely to have" does not mean the same as "always have" - it's describing a probability.

There is already one current thread concerning (just for a change) the merits of a GPC. 

One at a time is enough. This thread is reserved for its original purpose - anything other than technical discussions of ammunition design and performance will be deleted.

Not vacation, working.

Aortic repair conference, organising, chairing and co. Computer links not working, and crap.

Cardiac surgeons, cardiologists, sonographers, radiology working together to fix aortas from valve to iliacs.

Had a ripper CT of split mid aorta, blunt trauma, car vs tree.

Just an idea. I'll call it the 6.5mm ANMG, which stands for "Assault rifle 'N' Machine Gun", but really "Anthony-Nathaniel Middle Ground". ;) The idea is to explore a slightly different concept than what we've been discussing so far, which shouldn't be taken too seriously but hopefully will be thought provoking.

I based the case on the 6.5 Grendel, with the shoulder angle changed to 20 degrees and the case length increased to 40.3mm, neither of which matter too much but are based on preferences of mine. SolidWorks gives a case volume of 38.2 grains H2O, which sounds roughly correct if a bit optimistic. For all intents and purposes, this is like the Grendel, but I wanted to add a little more length so long bullets didn't intrude so much into the cartridge case. Below is the case and its volume-of-material:

The point of the round is to provide a lighter round than is possible given the GPC requirements, while still having the potential to meet at least some of the GPC requirements with heavier loads. To this end, the standard round would use a very light-for-caliber bullet of 85 grains; a weight easily achievable in lead-free form, such as an EPR. This round or a lead-free frangible training round could be used for training anywhere, and is useful for all squad-level small arms due to its light weight. In this ballistic example, the bullet used is flat-based, but it doesn't have to be; that's just the model I was using at the time:

Clearly, this does not meet Tony's requirements, but for those concerned about 5.56mm's terminal performance and the performance of .22 caliber rounds in general, it does have some interesting characteristics. For example, it gives almost 60% more energy at 500m than M855, while adding 40m onto the range at which M855 holds on to 2,000 or more ft/s velocity. It gives the same energy at 650m as M855 does at 500m, as well, plus an extra 40% energy at the muzzle. Sectional density is about the same, but given iron/copper alloy construction I don't think SD will be so important at short ranges anyway.

The round has a light bullet to make me happy - total round weight in brass comes to 15.23 grams - heavier than I'd like, but getting there. In steel, cartridge weight is 14.75 - still an increase of 23% over 5.56mm, but quite a bit better still than rounds like 7.62x39, 6.5 Grendel, or 6.8 SPC. So pretty light, all things considered.

Here's where I maybe make Tony happy - the light 85gr bullet satisfies the Army's requirement for a round that can be used in training ranges. The Army has shown that they will accept combat rounds with lead cores (e.g., Mk. 262 being used outside of SOCOM) as long as those rounds are not being used for training. Great, so here's where you cheat. If more range is desired, additional loads can be introduced or brought out from stores that have heavy, lead-cored bullets in either OTM (for DMRs) or steel-jacketed FMJ (for SAWs/MGs) bullets to meet those additional requirements, and these rounds can meet Tony's energy at a kilometer requirement. This does mean there would need to be additional suites of tracers, etc, but this problem becomes much easier if OWL succeeds, and anyway, there's a wide variety of tracer subtypes in service already. Again, in normal service everyone would just use the 85gr load and be pretty happy, but for special cases like Afghanistan the users best able to take advantage of longer-ranged ammunition have access to it. Further, the heavier projectiles are by definition more specialized ammunition, so their requirements can be adapted to whatever barrel length works. 

Loaded with the new Berger 130gr Hybrid just as an example, even the raw Powley values allow the round to handily meet the klick energy requirement from a 16.7" barrel:

And that even works out to a pretty good 17.47 grams cartridge weight, too.

This is just an exercise - I'm hoping it will spark some additional discussion beyond the normal GPC: good/bad? back and forth. I am not totally happy with this solution, and I suspect neither would Tony be, but it's maybe a meeting halfway between our two positions that we can be equally unhappy with. ;)

NathanielF said...

the biggest factor here is additional magazine weight

Would poly mags change the argument a bit?

I mean, where would be the sweet spot for case dimensions x loaded magazine weight, keeping projo weight the same? And how much case volume would this solution squeeze out?