Largest 5.56 based cartridges?

[CamoDeafie]

What are the largest cartridges based on either the 5.56 NATO or .223 Remington cases?
I keep thinking its the .300AAC blackout?

On another forum; a person mentioned putting a rim cut in his 300 BLK handi rifle and using .357 Magnum cases necked down to .300 for his rimmed .300BLK loads.. got me thinking; is it possible to get a custom barrel spec made, and to blow out the 5.56 case even more to say .327 or .338 caliber bullets if the 5.56 cases aint able to take 9mm/.357 cal bullets?

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[DizzyJ]

All it costs is money. You can order pretty much any reamer you want.

Now, powder charge and barrel holding up to said pressures may or may not be another issue altogether.

 

[B5Ben]

300blk is largest common cartridge that can think of. I'm sure there have been others to try something bigger, but nothing approaching viability that I know of.

 

[Certaindeaf]

Not based on the 556 but the WSSM's work on a AR upper, kinda. You have to have a whole new upper but the various calibers are pretty neat, like the .25 being around the 25-06 in power.. coming out of regular AR magazines/lower.
the, '06 on right and SSM on left

 

[Stomper]

Not based on the 556 but the WSSM's work on a AR upper, kinda. You have to have a whole new upper but the various calibers are pretty neat, like the .25 being around the 25-06 in power.. coming out of regular AR magazines/lower.
the, '06 on right and SSM on left

View attachment 393676

They look like they belong in a PEZ dispenser... LOL!

 

[KKG]

I seem to remember one of the Gun Writers, from long ago, who, for laughs, managed to get a .50BMG Bullet into a .223 case! Needless to say, he wasn't a fan.

 

[Lilhigbee]

7.62X40WT is 5mm longer than the .300BO with corresponding increase in performance for lighter bullets. heavy bullets for subsonic have to be loaded deep enough that there isn't any significant increase in useful volume. It does require modified mags for an AR. No reason there can't be full length .30 caliber derivatives as long as you don't put them in an AR. A bolt action could be readily chambered for it. Eliminate the shoulder and perhaps get a .338 bullet in it?? Haven't measured one to see what size a straight-wall case would be.

 

[CamoDeafie]

On another forum, someone posted a link to one of the pages of ar15 barrels website, describing a straight walled 5.56 case with a .357 bullet, called .357 Rimless.. and then on a search, found some posts by the guy who owns that website.. turns out the AR magazine design is what is preventing the larger bullets from feedig reliably due to the deep ribs for the bottleneck 5.56 cartridges.. although .300blk obviously works..

He also created a rather odd hybrid cartridge, .357 Auto, using the long 10mm cases necked down and spire pointed bullets, says they fit 6.8 SPC magazines, and uses 10mm bolt group I believe. Have not seen barrels for that yet. I wonder if .338 bullets would work in a 5.56 case without interference from magazine ribs.

 

[Lilhigbee]

I wonder if .338 bullets would work in a 5.56 case without interference from magazine ribs.

Probably not without a really short case length. The 35mm .300BO case length is that length to allow the .30 caliber bullets to clear the ribs. For my 7.62X40WT with the longer case length you have to use plastic magazines and remove the ribs to get them to feed.

 

[BillM]

Well--there did exist the .338-223 Straight. Quick eyeball of the case dimensions would say that if you
were to blow the 223/5.56 straight you should be able to get to a .356 bullet. Not sure you would gain anything over the 9x23 or the 9mm Winchester Magnum. Probably split the neck on the blow out-- Might get a usable
36-36.5mm straight wall case if you trimmed it to the 5.56 shoulder.

ETA--REALLY need to speed up my typing. TWO replies while I was getting this one done.

 

[3MTA3]

By largest do you mean the largest caliber or the most powerful?

Most powerful in a standard upper is the 6.5 Grendel. It carries the most energy, shoots the flattest and has the best wind resistance. I'd personally go with the AAC BO if I wanted fatter, but only in it's specialized role in a suppressed weapon.

 

[CamoDeafie]

By largest do you mean the largest caliber or the most powerful?

In caliber on 5.56 case. Looks like largest feasible is the .357 Rimless design; but can't be used in AR magazines. Might work in bolt action carbines though.
I am aware of the big bore .458 SOCOM, .450 Bushmaster and .50 Beowulf, also aware of the .375 SOCOM based on a .458 necked down, and the others like 6.5 and 6.8 and .277 Wolverine... but more curious of the "in between" cartridges on 5.56 cases if possible.

 

[DeanMk]

What are the largest cartridges based on either the 5.56 NATO or .223 Remington cases?
I keep thinking its the .300AAC blackout?

On another forum; a person mentioned putting a rim cut in his 300 BLK handi rifle and using .357 Magnum cases necked down to .300 for his rimmed .300BLK loads.. got me thinking; is it possible to get a custom barrel spec made, and to blow out the 5.56 case even more to say .327 or .338 caliber bullets if the 5.56 cases aint able to take 9mm/.357 cal bullets?

With a base diameter of .376" it is likely the largest caliber one could make based on this cartridge would be a .35.

 

[Jamie6.5]

Largest bore would be a .35, but SSK did build a .338 Whisper on the 5.56 case, which should be capable of shooting the 250-300gr class bullets with enough of a twist rate.

 

[titsonritz]

Largest bore would be a .35, but SSK did build a .338 Whisper on the 5.56 case, which should be capable of shooting the 250-300gr class bullets with enough of a twist rate.

Bingo

Here is a list of AR Calibers I have compiled based on the .223/5.56x45 case. It is a little dated as you will note the .277 Wolverine is not on it (yet)


.17x223*

.17 Remington*|**

.20 Practical*

.20 Tactical**

.20 Vartag

.204 Ruger*|**|***

.221 Fireball

.222 Remington

.222 Remington Magnum

.223 Wylde*|***

.223 Remington (5.56x45mm NATO)*|**|***

.223 Remington Ackley Improved

6x45mm (6mm-223)*|**

6mm TCU

<broken link removed> (not to be confused w/ 6×47 Lapua)

6mm Whisper (6x35mm PDW)

.25x45 Sharps*|**

.250 Myra (.222 Remington necked up to .25 caliber)

.25 Copperhead (25/222)

.25 TCU (.25 Ugalde, .223 necked up to .25 cal.)

6.5mm Whisper

6.5 MPC

6.5 TCU

7mm Whisper

7mm TCU

7.62x40 WT***

<broken link removed> *|***

.300 Whisper (.300/221, .300 Fireball)**

.338 Whisper #2


Partial Source: Here's a list of AR-15 Calibers...WOW!!!


* = AR barrels available @ <broken link removed>

** = AR barrels available @ AR15BARRELS.COM

*** = AR barrels available @ Wilson Combat

 

[DizzyJ]

Bingo

Here is a list of AR Calibers I have compiled based on the .223/5.56x45 case. It is a little dated as you will note the .277 Wolverine is not on it (yet)


.17x223*

.17 Remington*|**

.20 Practical*

.20 Tactical**

.20 Vartag

.204 Ruger*|**|***

.221 Fireball

.222 Remington

.222 Remington Magnum

.223 Wylde*|***

.223 Remington (5.56x45mm NATO)*|**|***

.223 Remington Ackley Improved

6x45mm (6mm-223)*|**

6mm TCU

<broken link removed> (not to be confused w/ 6×47 Lapua)

6mm Whisper (6x35mm PDW)

.25x45 Sharps*|**

.250 Myra (.222 Remington necked up to .25 caliber)

.25 Copperhead (25/222)

.25 TCU (.25 Ugalde, .223 necked up to .25 cal.)

6.5mm Whisper

6.5 MPC

6.5 TCU

7mm Whisper

7mm TCU

7.62x40 WT***

<broken link removed> *|***

.300 Whisper (.300/221, .300 Fireball)**

.338 Whisper #2


Partial Source: Here's a list of AR-15 Calibers...WOW!!!


* = AR barrels available @ <broken link removed>

** = AR barrels available @ AR15BARRELS.COM

*** = AR barrels available @ Wilson Combat

Nice list!

 

[titsonritz]

I seem to remember one of the Gun Writers, from long ago, who, for laughs, managed to get a .50BMG Bullet into a .223 case! Needless to say, he wasn't a fan.

That is an impossible configuration. The largest dia of 5.56 brass is 0.3759" [9.548mm] and that is at the base not the shoulder. There is no way a half inch projectile is going to fit it's fat a$$ in those skinny jeans.

 

[Certaindeaf]

By largest do you mean the largest caliber or the most powerful?

Most powerful in a standard upper is the 6.5 Grendel. It carries the most energy, shoots the flattest and has the best wind resistance. I'd personally go with the AAC BO if I wanted fatter, but only in it's specialized role in a suppressed weapon.

View attachment 393689

The 5.56 is the "largest" as it is the most common and efficient (you gotta carry them kill pills, don't ya know).
livin' large, baby!

lolz

 

[KKG]

That is an impossible configuration. The largest dia of 5.56 brass is 0.3759" [9.548mm] and that is at the base not the shoulder. The is no way a half inch projectile is going to fit it's fat a$$ in those skinny jeans.

I didn't say it was a workable configuration, I just mentioned it. As I remember it "he" suggested that a front loading cylinder was necessary. The author didn't think much of the .223 as a military round or for much of anything else. We already had the .222 and the .222Magnum as well as the .22-250. All of which in his opinion were as good as or better than the.223. He, like many others, felt the .308 was THE cartridge the Military Should have kept. Frankly, I agree with him on that point.

 

[Certaindeaf]

I didn't say it was a workable configuration, I just mentioned it. As I remember it "he" suggested that a front loading cylinder was necessary. The author didn't think much of the .223 as a military round or for much of anything else. We already had the .222 and the .222Magnum as well as the .22-250. All of which in his opinion were as good as or better than the.223. He, like many others, felt the .308 was THE cartridge the Military Should have kept. Frankly, I agree with him on that point.

Exactly, look at what happened in 'nam, man. lol