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Exploring The Design Space   Ammunition <20mm

Started 25/7/15 by NathanielF; 170138 views.
compost2

From: compost2

26/7/15

stancrist said...

CWRPHILLIPS said...

Jim Schatz's article on future assault rifles

There is a statement in there which I have not seen anywhere else: “Current U.S. statistics reveal that 21% of small arms KIA’s and WIA’s in Afghanistan are from 7.62x54R caliber weapons” does anybody know if it is true?

It seems to correlate fairly well with the chart on Tony's site:

In statistical terms misleading without for example separation into two classes, one: long range, and two: close range firefights as initiated by adversary, and for each two ratios: 7.62 x54 casualties per number of such fired, and ditto 7.62x39 casualties per.

Also useful to calculate similar statistics for firefights initiated by own forces where own suppression is more of a factor from the start.

Of course all the above is impractical without accurate wide-azimuth sound recording which can be essential for useful operational research.

                stancrist said...

CWRPHILLIPS said...

Assuming that most of the other 79% were 7.62x39mm it suggest that long range fire-fights are not the main problem; possibly not even a significant problem.

From what I gather, they are mostly harassing fire that inflicts few friendly casualties.  So yes, it does not seem to be a problem that requires a change to a GPC.

The tactical problem is that harassing fire can force friendlies to ground with loss of actual or potential initiative. Without prompt return fire - from for example own suitably long range MG and preferably light mortar, or in slower time (unless fully pre-arranged) friendly fire support - an adversary can more readily withdraw and/or manoeuvre some or all of its own elements.

A basic tactic for both sides is to draw them in rather than be drawn in. Also 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.

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

H_Minus

From: H_Minus

26/7/15

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? 

Msg 6327.23 deleted
NathanielF

From: NathanielF

26/7/15

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".

stancrist

From: stancrist

26/7/15

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.

compost2

From: compost2

27/7/15

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.

autogun

From: autogun

27/7/15

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.

 

In reply toRe: msg 27
autogun

From: autogun

27/7/15

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.

 

carniflex

From: carniflex

27/7/15

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.

In reply toRe: msg 1
NathanielF

From: NathanielF

27/7/15

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. ;)

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