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Exploring The Design Space   Ammunition <20mm

Started 25/7/15 by NathanielF; 126361 views.
QuintusO

From: QuintusO

19/6/20

I seem to have turned .204 Ruger into a GPC:

520 Vulcan. 1.76" case length, 2.56" COAL, Mach 2+ to 600m, 1,000m frag range, more energy at 1,000m than 7.62 NATO, lower CDFC at 1,000m than 6mm Unified, lower weight with steel case than M193.

QuintusO

From: QuintusO

19/6/20

Looks a bit strange in this guise to me, but the weight comes down to 8.81 grams per shot:



COAL is just 2.41", so magazines would be a reasonable size. I'm going to go back to the 570 and see what I can do with that one, too.

EmericD

From: EmericD

19/6/20

You could probably do better with the .17 Fireball and a 30 gr VLD bullet (and a COAL lower than 2", or maybe a Neckless version of the .17 Remington, with a 39 mm case).

QuintusO

From: QuintusO

19/6/20

EmericD said...

 

You could probably do better with the .17 Fireball and a 30 gr VLD bullet (and a COAL lower than 2", or maybe a Neckless version of the .17 Remington, with a 39 mm case).

 

Sounds like 500 Hellcat:



37gr 4.85mm at 3,500 ft/s from a 12.8" barrel. 6.4 grams weight. 1.985" COAL.

So I've been down that road far enough to design an entire rifle and five different kinds of magazines for it, the achilles' heel is poor barrier performance from bullets that light:

QuintusO

From: QuintusO

19/6/20

Something I think is invaluable are the opinions of non-experts. I will routinely ask my wife (who knows everything she does about guns from me) for advice, for example, and I will poll friends of mine in other industries for a sanity check. I did so regarding these new Power Series projectiles Gripen designed, and how they might change optimization factors within the context of infantry small arms ammunition.

The consensus was that low drag projectiles will re-emphasize performance at the muzzle during ballistic evaluations, where before downrange requirements might have sufficed. The reason is, they're so efficient that they may effortlessly meet benchmark performance values at distance, without meeting some requirements closer up. In sum, their performance curve is so much flatter (significantly less variation between start and end performance states) that they may need to be optimized for muzzle/near combat values. This is a phenomenon I encountered when I first started working with VKOs, and the 500 Hellcat itself is a great example. It can meet requirements as exotic as beating factory .260 for drop and drift at 1km, yet at the muzzle it has less than 1,400 J. And the best calculators I have access to indicate this has a very negative effect on its ability to penetrate barriers like concrete, with the light 37gr bullet. Ultimately, these limitations and the failure to meet the ammunition density level I desired resulted in me rejecting the 500 Hellcat - and even preferring to neck it up to .22 caliber (which is very rare for me).

So for my next spectrum study, I think I will create a suite of requirements set at 0-200m, and on top of that the usual gang of distance requirements (probably limited to 600m). I would like to consider a breadth of projectile styles, such as the VKO-Mk.3, the VKO-Short, and the Gripen Power Series. That's where I'm headed from here. Exciting!

EmericD

From: EmericD

20/6/20

QuintusO said...

37gr 4.85mm at 3,500 ft/s from a 12.8" barrel. 6.4 grams weight. 1.985" COAL.

So I've been down that road far enough to design an entire rifle and five different kinds of magazines for it, the achilles' heel is poor barrier performance from bullets that light:

Sorry, I don't understand...

You rejected this design because you were not able to provide a large capacity magazine (something nearly useless for an IW as long as you can have a 20/25/30 rds mag, according to your own analysis), and you choose to increase the cartridge & weapon weight (and recoil) in order to "kick more dust" instead? (I noticed that using a heavier bullet to "kick more dust" is baaaaaaaad, but using a heavier bullet to provide barrier penetration no 5.56 mm load can match, seems legit).

With a short round like the .17 Fireball or the .500 Hellcat, it seems possible to replace "double stack 5.56 mm pouch" with triple or quadruple "side-by-side" pouch, allowing the soldier to carry up to 9-12 magazines on his chest / waist instead of the current 6 (in 3 x double stack pouches).

With the sub-0.7 i7 FF you are using in your calculations, the BC of a 30 gr / .172" bullet will be higher than 0.20, so even with a MV of "only" 3300 fps you're supersonic up to 1 km, or use a 20-25 gr bullet and duplicate exactly the external ballistics of the vaunted ".21 short range (6/10)" of the 1952 "Hall report".

QuintusO

From: QuintusO

20/6/20

EmericD said...

You rejected this design because you were not able to provide a large capacity magazine (something nearly useless for an IW as long as you can have a 20/25/30 rds mag, according to your own analysis),

I created that analysis because of the results I got from Hellcat. I had had the thought for a few years that each round in your magazine does not have equal importance to the shooter. After Hellcat showed that it was probably impractical to reduce the size of the ammunition enough to facilitate very high capacity magazines, I got more interested in what capacity of magazine made the most sense. It seems obvious that the 20-round magazine of NGSW is not enough (indicated by the demand for 30 round magazines in Vietnam, Rhodesia, and other conflicts). 

So I thought for a bit about how to quantify that difference in value. Uptime is the most direct way to do that. So Hellcat -> the uptime analysis.

EmericD said...

and you choose to increase the cartridge & weapon weight (and recoil) in order to "kick more dust" instead? (I noticed that using a heavier bullet to "kick more dust" is baaaaaaaad, but using a heavier bullet to provide barrier penetration no 5.56 mm load can match, seems legit).

Is this a rational response? Yes, I put different weight on different metrics. Is that a surprise? Wouldn't it be very poor analysis indeed if everything were weighed the same?

Also, you've omitted the real reason I rejected Hellcat: The payoff never materialized. I am willing to accept the drawbacks of micro-caliber ammunition, if there is a substantial payoff. If practical, compact large-capacity magazines are not possible, then the case for this sort of round kind of falls apart.

Also not sure why you're saying no 5.56 round can match that barrier pen, because 5.56 Super does, according to the calculations I'm using. We could argue back-and-forth about whether those calculations are representative, but that was one of the criteria I was using when analyzing Hellcat.

EmericD said...

With a short round like the .17 Fireball or the .500 Hellcat, it seems possible to replace "double stack 5.56 mm pouch" with triple or quadruple "side-by-side" pouch, allowing the soldier to carry up to 9-12 magazines on his chest / waist instead of the current 6 (in 3 x double stack pouches).

You can sort of do that, yes. The Hellcat 30 round magazine could be carried four abreast instead of three abreast, but not three-deep instead of two-deep. So you could carry 240 rounds on your chest instead of 180. The 45 round magazines (as everyone who's seen them has pointed out hahahah) are about three inches longer than a 5.56 PMag, so while you can carry 45 rounds in the same way, you also could carry 40 round PMags instead. Here's a size comparison:

L to R: 5.56mm polymer mag, 5.56mm F-4 mag, Hellcat 60 round quad stack, Hellcat 45 round double stack, Hellcat 30 round mag, Hellcat 20 round mag.

EmericD said...

With the sub-0.7 i7 FF you are using in your calculations, the BC of a 30 gr / .172" bullet will be higher than 0.20, so even with a MV of "only" 3300 fps you're supersonic up to 1 km, or use a 20-25 gr bullet and duplicate exactly the external ballistics of the vaunted ".21 short range (6/10)" of the 1952 "Hall report".

Yeah, the exterior ballistics are great:

And like, if the 500 Hellcat sounds good to you, I suppose that's fine. But since the ammunition density didn't shake out how I wanted, and there were some real penalties, I decided to pursue other concepts.

QuintusO

From: QuintusO

20/6/20

EmericD said...

you choose to increase the cartridge & weapon weight (and recoil)

Not by much, for the record. Tigershark weighs less than 90 grams more than Hellcat. 

The cartridge weight went from 6.4 grams for 500 Hellcat to 7.45 grams for 5.56 Super. Magazine weight for 500 Hellcat is 168 grams for a 45-round magazine. A PMag 40 is 179 grams for a 40-round magazine.

That means you can carry 99 rounds per kilo for 500 Hellcat (45 rd mags). You can carry 84 rounds per kilo for 5.56 Super (40 rd mags). 200 rounds of 5.56 Super weighs 2.385 kg. Within that same weight, you can carry 225 rounds of 500 Hellcat, at 2.280 kg. A 105 gram difference with 25 extra rounds. Is that worth an entirely new caliber that isn't backwards compatible? In my view, no.

QuintusO

From: QuintusO

20/6/20

And like, I'm not in favor of flechettes, either? So I'm not sure why this is surprising.

poliorcetes

From: poliorcetes

20/6/20

How do you calculate frag range? just speed or do you add up another variables?

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