Thread 64155343

We all love 5.56 for it's good performance, low recoil, and rim diameter smaller than 9mm parabellum which means short mags with good capacity.

But could we make something similar with better long range capability without sacrificing (much) of it's good characteristics?

My suggestion would be to keep the case dimensions, increase OAL by ~1/4'' for a longer and pointier ~90 grain bullet, replace the case material with either polymer or NAS3 and increase the pressure a bit, nothing too crazy, say, to 70 kpsi.

This would result in about the same muzzle velocity, maintaining the excellent point blank range, a more aerodynamic bullet for longer range and recoil that is still within intermediate caliber range. Yes it would require a new rifle with a slightly longer mag well and action and a stronger bolt but other than that nothing too drastic.

Yes we can, and we should. Picrel is something I mocked up (poorly).
>left: 5.7x28
>middle: the subject of this post
>right: 5.56x45

The transformation required to get from 5.56 to this thing is as follows.
>shrink case head to 9mm (30 carbine)
>cut case down to 1.35”
>cut OAL down to 2.1”
>increase pressure to 80kpsi

Load it with a very fine, 5 caliber long bullet (i7≈0.8) and load the case to 80kpsi. When I calculate case capacity and input everything into the powley computer, it returns a muzzle energy of 1250ft*lbs from a 16” barrel, with ~770ft*lbs retained at 300 yards. ~100ft*lbs less at the muzzle than m855a1(20”), but about 100ft*lbs more at 300yds. So in other words, the ballistics of the 5.56 can be duplicated/slightly exceeded with a cartridge shorter, skinnier, and much lighter. So if you want better performance, simply scale the whole thing back up to 5.56 size.

I thought the thing I mocked up would be a pretty good cartridge to feed from quad stacks. The smaller case head reduces the width of the magazine by about 0.1” and increases capacity by ~5 rounds. The main point of quad stacks being that they allow a long duration of full auto fire and are also the most mass-efficient way of feeding ammo. A 5oz PMAG weighs 73 grains per round, but a 7oz quad stack (a bit heavier than the Surefire), loading these 9mm case head cartridges desert tech style (all the way up) weighs 38 grains per round for an 80 round capacity. Pretty dope. And if you were using NAS3 cases (not sure if they support 80k, but they do support 70k), the case would be about 45 grains lighter than a brass 5.56 case. That’s 2.4 pounds saved over a 210rd load just by way of a lighter case and quad stack mags.

It's more expensive but you could squeeze about 30% more chemical energy into the cartridge if you replaced the nitrocellulose with a mixture of ammonium perchlorate and starch.

>>64155512
I don't think reducing OAL is smart since it doesn't really improve magazine capacity and while it does make the cartridge case shape more weight efficient I don't think that it's worth it.
But I agree that a long and fine bullet with higher pressures would be an excellent improvement.

>>64155522
>fires 3 rounds
>weapon is jammed
Great job.

>>64155605
Also now you have kidney failure from exposure.

>>64155522
>>64155512
>>64155343 (OP)
How are you all planning on stabilising a 22 caliber projectile that's in the order of about 1/4 longer (didn't calculate it) than 5.56x45?

>>64155343 (OP)
My idea is much simpler, neck up 5.56 to 6.5 and retain the same case length. You'd have a wider projectile that'd allow for heavier bullets which means better subsonic performance while not completely abandoning the flat trajectory of 5.56 since 6.5s tend to fly pretty flat too compared to 7.62s

>>64155343 (OP)
6.5 creed is like a cross between 308 and 556.

>>64155343 (OP)
>>64155512
You're right and anybody criticizing you is retarded and should look up 5.56 FABRL and 7.92 CETME. High aspect ratio bullets are the future.

>>64155607
It’s only 5 calibers long. It’s Not exactly a difficult feat to stabilize such a projectile. The Berger twist rate calculator outputs that a twist rate of 1:6.5” is sufficient for a 60gr bullet (1.12”, G7BC=0.21).

>>64155609
God, now we have to deal with your autism for the next week or two until we either bully the special interest out of you or bully you away from this site. Subs are a meme!!

>>64155616
Yea, my long ass wall of text could have just been summarized with “5.56 FABRL but 80kpsi 30 carbine case”.

>>64155607
It's nowhere near a problem length yet.
Some of the most accurate cartridges known to man have much finer bullets.

>>64155623
>Not exactly a difficult feat to stabilize such a projectile
>a twist rate of 1:6.5” is sufficient
Your bullet will not survive that. You need to theorycraft and post about it less and handload more. 90gr 224 at around 5 calibers length starts failing from a 1 in 7 barrel at about 2800fps. You are proposing to increase it to 1 in 6.5 (or more) and push the velocity of what? 3150fps like M855A1? That's 350,000 RPM. Your bullet is going to fly apart.

>>64155680
Yes, 3150fps. The rifling angle is hardly a problem, you could drive a .224 through a 1 in 2 twist barrel and not exceed the engraving angle of 1:3 8.6 blackout. 1 in 6.5 is >3x slower (at equal velocity) so again, it’s not a problem.

And it’s not rpm that blows a bullet apart - it’s angular velocity.

>>64155605
A long recoil mechanism could handle it.

>>64155639
>5.56 FABRL but 80kpsi 30 carbine case
Add polymer case (which you did above), and now this is a list of my favorite firearms concepts. Nice.
>>64155680
8.6 Nigger supers spin at 500,000+ RPM with a larger diameter projectile and don't seem to have too many problems.
CETME used a lightweight aluminium jacket but a copper bearing surface, IIRC this increased its moment of inertia and made it more stable for a given twist rate.

>>64155692
You are not considering jacket thickness constraints properly, and, again, you need to go and actually do some load workup and shooting IRL instead of arguing with me, because you will discover very fast that actually existing 90gr 224 bullets do not survive 3150fps from even 1 in 7 barrels with any reliability.

>>64155714
>8.6
Have rather more diameter to give over to jacket thickness than anything you'll be able to achieve trying to get a 5.7mm bullet to 90 grains. The spin related failure mechanism for bullets is jacket failure.

>>64155717
So increase jacket thickness by a fraction of a millimeter until they’re not exploding. I’m not talking about taking off-the-shelf bullets meant to be shot through slow twist barrels and spinning them much faster (no such medium weight VLD’s exist). 1 in 6.5 for a .224 bullet is hardly fast. Ffs there are 1 in 5” twist 300 blackout barrels out there imparting 1.8x the angular velocity on bullets of equal velocity. How come those bullets don’t explode?

>>64155714
>>64155692
Also, ten seconds of searching tells me that the ammo and twist combination you are talking about suffers from jacket failure at very low velocities (they almost need to stay subsonic from 1:3).

>>64155741
Stop theorycrafting at me and go make some loads to prove me wrong. Plenty of other people in the PRS community have tried pushing 90gr ELDM 224s out of barrels, and it doesn't work at the velocities you want from a service rifle. But go and prove me wrong. I'll wait.

>>64155760
You know how common a 1 in 7 twist 5.56 barrel is? You’re telling me the twist rate of these 1:7 barrels is 7% away from inducing jacket failure?

>>64155512
Sounds good. I have 2 questions.
Long ogive bullets having longer lever to bend like broken pencil lead. Does neck length also needs to be increased to scale?
How to reach 80k psi reliability like 60k psi did? Because the proofing load is going to be 100k or 120k.

Checkout 5.45x39

>>64155792
>Long ogive bullets having longer lever to bend like broken pencil lead. Does neck length also needs to be increased to scale?
Not a problem.
>How to reach 80k psi reliability like 60k psi did? Because the proofing load is going to be 100k or 120k.
Not really a problem, as long as the bolt is strong and the case as well only thing those higher pressures cause is increased wear which doesn't matter for proofing.
>>64155849
It's ok but it's too slow, weak, and light weight bullet.

>>64155623
Well they've been trying to bully me off this site for over a decade now, you're not going to be the one to do that. As for bullying it out of me, I think I've gotten it out of my system, for now. I don't have the right tools but mark my words when I do you WILL see regular threads of my 6.5x45 autism project

>>64155760
>go and prove me wrong. I'll wait.
Sperg he's talking about new bullets being designed for the cartridge and as he's pointed out, it's been done in other calibers.

>>64155769
In 90gr ELDM bullets, yes.

>>64155609
>while not completely abandoning the flat trajectory
it's subsonic, its going to have a trebuchet trajectory no matter what you do, retard.

>>64155944
Then jacket thickness is not the problem and caliber does not pose a significant enough restriction on jacket thickness. If there exists a 55 or 62 gr .224 bullet that can be fired from a 1:7” barrel at 3150, then any .224 bullet of any mass can be fired through, and so long as bullet construction is the same, it’ll be fine.

>>64155892
Don’t use a 45mm case. Cut it down significantly. Look up “6.5 creedless”. That’s actually a pretty gangster SBR cartridge.

>>64155609
Why the fuck do you want gay ass subsonic bullets that are only good for LARP:ing and shit?
Why would you want to force such a cartridge for the average soldier?

>>64155952
It's going to have both super and subsonic loads, dumbass

>>64156041
Dang that is pretty neat
>>64156075
Not every cartridge is for soldiers. Also fuck them, the brass doesn't make them suffer enough anymore which means war movies suck now. The average suffering of a grunt is directly proportional to the quality of war media released at the same time

>>64155343 (OP)
>5.56
>good performance
stopped reading right there

>>64155609
>since 6.5s tend to fly pretty flat too compared to 7.62s
That's because of their ballistic coefficient, which you won't have if you're just necking up 5.56 without changing anythinig else.

>>64155343 (OP)
State of the art.
3rd from the right is 64 grain 5.56 bullet, copper solid. G7 BC .208 radar confirmed. Stabilised at 2700 fps with 1:7 twist.

Of course ogive is too long to fit in the existing 5.56x45 but will fit in your proposed 5.56 2.0.

Another thing about that idea I like you can make new caliber reverse compitable with 5.56x45 and able to use old 5.56 in new guns. It's very useful for smooth transition to a new caliber and guns.

>>64155343 (OP)
>>64155512
Hornady ELD-X 80gr has a G7 BC of .244 and it's about 4.5 calibers long. .221 Remington Fireball is a 5.56 case cut down to 1.400". You could easily load these to 2.260" OAL and feed them through a Qmag. The problem with very heavy bullets in small cases is that you end up with a very small range between underloading and losing significant performance, and overloading and blowing things up.

>>64155343 (OP)
For what purpose do we need shorter OAL, abandon the AR mag well, do something new.

>>64157570
I don't think OP proposes shorter OAL.
Same case + longer bullet = longer COAL.
But yeah fuck AR-15 magwel and magazines.

>>64157382
>Hornady ELD-X 80gr has a G7 BC of .244 and it's about 4.5 calibers long
This bullet >>64157276
Has better form factor that ELD-X 80gr.

>>64157276
How come bullets IRL typically fall (quite a bit) short of what is theoretically possible with a given L:D? I say typically and ask the question because I can not chalk it up to “because zero yaw with no surface imperfections can’t be done IRL”, because Warner Tool’s Flatline bullets actually seem to have almost the lowest possible drag coefficient. For example, their 155.5gr .308 bullet is 4.7 calibers long and has an i7 of 0.8. Spectacular to say the least.

Picrel is a 5 caliber bullet I modeled with an i7 of 0.8 (at Mach 2.5). But if I went and made this and shot it through a 10 yard and 200 yard chrono, the rate of deceleration would betray a higher form factor. Why is this?

The bullet you posted looks extremely fine and I would think it’s ff is also much closer to 0.8 but alas, it’s 0.87.

>>64157788
He may have meant to reply to my post, the first reply in this thread. Another anon thought OP and I were the same person because our suggestions were so similar.

>>64157382
There is an anon here who has done just that, but I think he used a heavy v-max bullet.

>0.244G7, 80gr .224
That’s an i7 of 0.93. Much better than 5.56 but not as good as it can be.

>>64157382
>4.5 cals long.

You mean this?
https://www.hornady.com/bullets/rifle/22-cal-.224-80-gr-eld-x#!/

That’s ~5.3 cals long. 0.93 isn’t a great form factor for that length.

>>64157147
Interesting. I thought ballistic coefficient was specific to the projectile where it describes a ratio to width, length, and mass. My mistake I'm not in to the reloading game so I know damn near dick all but still I think there's a place for a middle ground between 300blk and 5.56. Something that has decent subsonic/ SBR performance while still being not dogshit when fired supersonic from a rifle barrel

>>64158858
I’ll give you a quick run down.

BC is sectional density divided by form factor. Sectional density is how much momentum the projectile has, and form factor informs how much momentum is lost to the atmosphere. You want to have high momentum (SD) such that what is lost to the atmosphere represents a small % of total momentum, so you don’t lose much velocity. And you want the momentum list to be low as well, hence the very fine bullet shapes used in long range shooting.

The formula for G7BC is as follows:
>Grains/7000/caliber/caliber/form factor
(Caliber in inches)

Form factor has to do with bullet shape and as such doesn’t change if you isometrically scale a projectile. But sectional density does increase by the scaling factor because the bullet becomes longer. Its frontal area increases by the square of the scaling factor, but mass increases by the cube. That’s why 50BMG bullets have such ridiculously high BCs - it’s because they’re so much longer compared to smaller caliber bullets.

>>64155343 (OP)
If you’re going to spend all this time and money on a new round, you might as well make it effective enough to defeat modern armor at long distances. You want 6.8x51/.277 fury. Might as well bullpup it too, if you can. Maximize barrel length.

Otherwise just stick with 5.56. It’s good enough that trying to alter it like this isn’t worth it.

>>64158902
Fascinating, I'm learning so much despite being immensely inebriated. I'll go back to the drawing board and try to apply that math to my hypothetical intermediate 5.56-300 round. Genuinely, from the bottom of my heart, thank you for the info and not being an ass about it. I know how anons can get when dealing with someone not in the loop and I'm grateful you spared the insults

>>64155343 (OP)
>Contrarian autists have to come up with absolutely ridiculous meme rounds to compete with 556 out of an 11.5 PSA shitrod

>>64158926
Thanks for the nice words bro

>hypothetical 5.56-300 round
I assume this is for good super and sub performance. I think the best way to do it would be to CETME-style. A large caliber, very long and fine bullet, but also very light for caliber. So it can be pushed at >3000fps and still retain a decent BC. So, low sectional density, but also very low form factor. Such a bullet could be larger in caliber than 5.56 and still retain the same external ballistics. This helps with subs because now the bullet is super wide and so you can use long, dense, heavy subs. Imagine a 350 legend with ultralight VLDs that can also be loaded with ultraheavy subs

>im grateful you spared the insults
You’re welcome, faggot.

>>64158906
It's really funny when you post this in a thread about an improved 5.56 when 6.8 Fury is just an improved 7.62 lol

>>64158751
Angle of attack of flight.
They don't fly strictly nose forward and that is increasing drag.
BTW there are tangible and detectable difference bettwen ballistic coefficient of same bullets fired from test bull barrels that stabilise bullets better than actual weapons barrels.
Cheytac has patent about bullet form and twist rate chosen that way that bullet gyroscopic stability remains constant over course if flight, so bullet flies with minimal angle of attack and therefore drag (usually bullets become over stabilized as velocity decreases).

>>64159386
…yeah, that’s the point

>>64158906
5.56 already defeats 85% of body area at 1200 meters. Tiny ass cope plates protection ability is over blown.

>>64159553
Battle rifles are gay
You're gay.

>>64159386
There is nothing wrong with improving both 5.56 and 7.62. These are different use and both suck in the current design because of the bad form factor of the bullets.

>>64159551
>cheytac figured out how to keep stability constant

How? To do this, linear and angular velocity need to decrease at the same rate, right? How are they accomplishing this?

>angle of attack
Yeah that makes sense. If the bullet remains perpendicular to earth but is dropping, it’s presenting a greater area in the direction of travel. When does this start to really become a problem? Is it a problem inside 300 yards with an MV of ~3,000fps?

>>64159581
>To do this, linear and angular velocity need to decrease at the same rate, right?
Yes.

>How are they accomplishing this?
By designed form that has matched rotational drag so spin rate decreasea accordingly

>>64159581
>When does this start to really become a problem?
AoA history of the real projectile.