Substitutes for the 5.56 mm round


#1

I would like to write down a list of the cartridges developed for the AR platform to replace the 5.56 mm round
Military and civilian use …wildcats too


#2

6,5mm Grendel and 6,8mm SPC are two I’d say are amongst the most important ones.


#3

.300 AAC Blackout


#4

On the big bore side: .499 LWR, .50 Beowulf, .450 Bushmaster, .458 SOCOM.


#5


#6


#7

P.S. There’s also the .30 HRT from Teppo Jutsu which is basically the 6.8 Rem necked out, and various smaller Whisper rounds in calibres like 6mm, 6.5mm and 7mm, and other (mostly wildcats) made by necking up the 5.56mm case to 6mm, 6.5mm, 7mm.


#8

.500 Phantom
Zac


#9

Thanks all

Tony, I have an unknown wildcat in my collection that I labeled as “300 Whisper 37.5 mm case” .
It is made from 223 Rem brass and looks like the 7.62 x 37 HK.

Could you give me some dimensional data of your round?
For example case lenght, rim to shoulder lenght and neck lenght


#10

Hornady made the 6x35mm TSWG. TSWG (Technical Support Working Group) is a contracting pool for various agencies involved in anti-terrorist activities. Headstamp Hornady 6x35mm TSWG.


#11

[quote=“cartguy”].500 Phantom
Zac[/quote]
I think that the .500 Phantom is intended for AR-10 length actions rather than AR-15, and some loadings are longer than that - see the Teppo Jutsu lineup below.

From left to right: .30 HRT (110 grain Hornady V-Max); .338 Spectre – 300 grain Sierra Hollow Point Boat Tail Match King) and 300 grain HAWK Round Nose; .458 SOCOM – 300 grain Barnes X Spitzer, 400 grain Barnes Round Nose Solid and 600 grain Barnes Original; .500 Phantom - 168 grain Sierra HPBTMK (saboted), 700 grain HAWK and 750 grain Hornady A-Max


#12

I have one of them, and a 6x35 KAC PDW, and can’t see any difference between them - are they related or is it a coincidence?


#13

[quote=“Pivi”]Thanks all

Tony, I have an unknown wildcat in my collection that I labeled as “300 Whisper 37.5 mm case” .
It is made from 223 Rem brass and looks like the 7.62 x 37 HK.

Could you give me some dimensional data of your round?
For example case lenght, rim to shoulder lenght and neck lenght[/quote]

Case length 37.2mm, shoulder height 29.2mm, neck length 6.8mm.

The headstamp on mine is 7.62x37 HK RG 00 (with that funny stylised “HK” logo - rather cute!).

This round was developed as a joint project by Heckler & Koch and Radway Green for the HK SL9 SD integrally suppressed sniper rifle. I don’t know if anyone bought it.

Incidentally, there is another 7.62x37 round on the 5.56x45 case - the 7.62mm Musang from the Philippines. This was designed by the Government Arsenal there for use in a modified M4 carbine. Last I heard it was still in development. I don’t have measurements but it features a shorter neck and higher shoulder than the HK round. See: viewtopic.php?f=8&t=13319


#14

[quote=“TonyWilliams”][quote=“Pivi”]Thanks all

Tony, I have an unknown wildcat in my collection that I labeled as “300 Whisper 37.5 mm case” .
It is made from 223 Rem brass and looks like the 7.62 x 37 HK.

Could you give me some dimensional data of your round?
For example case lenght, rim to shoulder lenght and neck lenght[/quote]

Case length 37.2mm, shoulder height 29.2mm, neck length 6.8mm.

The headstamp on mine is 7.62x37 HK RG 00 (with that funny stylised “HK” logo - rather cute!).

This round was developed as a joint project by Heckler & Koch and Radway Green for the HK SL9 SD integrally suppressed sniper rifle. I don’t know if anyone bought it.

Incidentally, there is another 7.62x37 round on the 5.56x45 case - the 7.62mm Musang from the Philippines. This was designed by the Government Arsenal there for use in a modified M4 carbine. Last I heard it was still in development. I don’t have measurements but it features a shorter neck and higher shoulder than the HK round. See: viewtopic.php?f=8&t=13319[/quote]

Definitively my round is not a 7.62 x 37 mm HK. Dimensional data are close to your sample but not identical.

My round:

case lenght: 37.60 mm
shoulder height: 30.40 mm
neck lenght: 5.69 mm

I’d really like to know the proper name for this cartridge, but to date I have been not able to find a wildcat cartridge with those dimensions


#15

Hi Pivi,

Here are a few more:

From the SPC series, there are also the 5.56 and 7.62 full and rebated bases.

.300 Whisper and a couple of earlier rounds and the 7.62 x 37 and one of it’s developmental rounds.

Straying a bit due to rim/head diameter is the .30 Remington AR and its predessor the .300 American.

Paul


#16

Marco

Don’t forget, there were several cartridges used in the prototypes of the AR before it was finalized and before the 5.56 x 45 cartridge was developed. They don’t meet your criteria but they are important in the history of the AR.

222Remington, 222 Special, 224 Springfield, 224 Winchester come to mind.

Ray


#17

Thanks Paul,

…what the hell is the 300 American? Is it the same as the 308 x 1.5 Barnes?

I know that the 6.8 mm SPC case has became a very used parent cartridge for several wildcats. I think that it has been necked up at least to .338"

Is the 7.62 version also called 30 HRT?


#18

[quote=“Pivi”]
I know that the 6.8 mm SPC case has became a very used parent cartridge for several wildcats. I think that it has been necked up at least to .338" [/quote]

That would be the .338 Spectre I showed a photo of earlier, although to be precise that is based on the short-lived 10mm Magnum pistol round which has the same external base dimensions.

Teppo Jutsu’s version of it is (stands for Herrett Rimless Tactical, in case you anyone was thinking that it meant Hormone Replacement Therapy…). There may have been others (there usually are!).


#19

Pivi, your “list” is developing into a multi-volume effort.


#20

Armi & Tiro magazine has asked me to write down an article about these new cartridges for the AR 15 platform, since rounds like the 6.8 SPC and the 300 Blackout are becoming interesting for italian shooters.

An article previously released described the larger ones, from the 458 SOCOM to the 502 Thunder Sabre, so I am planning to describe the small-medium bores.

Paul, what the hell is the 300 American? I have the 30 American in my collection, but your rounds appear to be very similar to the 308 1/2" Barnes.

Ray… better not write the 5.56 story too…the magazine has not a large number of pages…and authors are stingy, so a 4 pages article is the limit, beyond they could call it “overbore”