6mm Lee-Navy shall be vindicated! Hybrid cases at high pressure, let's go with a 120-125 grain boat tail instead of a 135 round nose.

stancrist said:

I can't help but wonder if it may be possible to have one caliber that combines the advantages of both SCHV and full-power ammo into a single "have your cake and eat it" round.

The 6.5x43 mm could be an option. Weight neutral compared with the 5.56 mm, but 7 magazines will carry 175 rds instead of 210 rds. The plus side is that each round will deliver +60% of muzzle energy, and +100% at 500 m.

The 260 Remington using "high capacity" steel case and firing a 95 gr class bullet is another option (7.1 g case + 6.2 g bullet + 3.3 g powder + 0.4 g primer = 17 g cartridge), but only 140 rds available instead of 210 rds, but this combination seems very effective.

EmericD said:

The 6.5x43 mm could be an option. Weight neutral compared with the 5.56 mm...

The 260 Remington using "high capacity" steel case and firing a 95 gr class bullet is another option...

Unfortunately, while 6.5x43 and .260 REM keep weight down, both still have the bulk disadvantage of 7.62 NATO/6.8 NGSW; magazines are just as tall and MG belts just as long.

The only way to get reasonably close to having the whole assault rifle "cake" is if case diameter is no bigger than that of .224 Valkyrie, and preferably smaller (a la 6x45mm SAW).

Below, l. to r. -- .224 Valkyrie / 6x45 SAW / 5.56x45

Farmplinker said:

6mm Lee-Navy shall be vindicated! Hybrid cases at high pressure, let's go with a 120-125 grain boat tail instead of a 135 round nose.

LOL.  That brings back an old, long forgotten memory. 

Way back when I was thinking up my 6mm Optimum, my first effort at making a dummy round was to take a 6mm Navy case, shorten the neck and stuff a 6mm SAW 105gr FMJ bullet in it.

The result was virtually identical to the Russian 6x49 Unified cartridge (below, middle).

stancrist said:

The only way to get reasonably close to having the whole assault rifle "cake" is if case diameter is no bigger than that of .224 Valkyrie, and preferably smaller (a la 6x45mm SAW).

So, your only option is a +P+ 224 Valkyrie in SIG hybrid case, which may be not effective enough in the support role.

The Russian 6x49 mm is an interesting round, credited with a MV of 1150 m/s from a 72 cm / 28.3" barrel.

At first glance and using the case capacity of the .25 Savage, you need 73,000 psi to push your 5 g / 6.2 mm bullet at 1150 m/s / 3770 fps.

With the same pressure and a 13.5" barrel to keep the rifle length / weight around the M4 form factor, the predicted velocity is still around 1 km/s. The bullet BC is already OK with a C7 of 0.197.

Very interesting.  Thanks, Emeric.

stancrist said:

I can't help but wonder if it may be possible to have one caliber that combines the advantages of both SCHV and full-power ammo into a single "have your cake and eat it" round.

That was the very rationale for my "6mm CAKE" concept of an 85gr VLD @ 3000fps. Fragmentation range beyond 7.62x51, recoil equal or less then 7.62x39, with cartridge weight comparable to 5.56 Brass, all while keeping 30rd mags. 

Initially the idea was a 6mm HAGAR in Shell Shock or Polymer for the case. Thats just a slightly lengthened 6.8 SPC, so 30rd mags the same length as the LWRC Six8, just a bit longer COL (~2.4-2.5").

However with SIG's 80kpsi case technology, I wonder whether a 6x45mm (5.56 necked up to 6mm) at 80kpsi would be able to drive an 85gr @ 3000fps from a 16" barrel? 

(6x45 with 105gr VLD to show concept; 85gr EPR and SIG hybrid case would be the high pressure CAKE)

That would really keep everything pretty close to 5.56 weight and mag capacity. Just need a longer COL. 

Very surprising development.

Steyr is showing a 7lb rifle capable of firing both 7.62 and 6.8x51:

https://www.thefirearmblog.com/blog/2023/03/01/enforcetac-2023-steyr-dmr/

The goal of the new Steyr DMR was to reach a combination of accuracy and lightweight design. To this end, Steyr’s new DMR is said to be a sub-MOA rifle that is capable of shooting .277 FURY/6.8x51mm, .308 Winchester, and 6.5 Creedmoor. The piston-driven system also features a reversible charging handle making the Steyr DMR much easier to adopt for both left and right-handed shooters. Steyr DMR doesn’t require a buffer tube to operate and therefore it features a folding stock, that is compatible with any off-the-shelf AR stock. The rifle can also be fired with the stock folded according to Steyr.

The rifle features four different gas settings for regular conditions, adverse conditions, gas-off, and then a silencer setting that is also meant to be used with subsonic ammunition. The rifle also features a “quick change barrel system” that requires only a torque wrench to swap out. Steyr has said that although it’s called a quick change barrel system, it really meant to simplify the process for armorers rather than to serve as an in-the-field barrel change system. Lastly, the rifle will make use of regular AR-10/SR-25 pattern magazines.

The Steyr DMR has been in development for about two years and the plan is to have the rifle start going into production by the end of 2023 in Europe, Steyr has said that they are even ready to take orders for the rifle right now. 

YouTube

NEW Light and Accurate Steyr DMR Piston AR-10

In this episode of TFBTV Show Time, @JamesReeves is at EnforceTac in Germany to speak with @Steyrmannlicher-rifles about the new Steyr DMR. The Steyr DMR is...

''Ar15 master race'' folks must at one point consider its not AR15 or Ar10 when there is practicaly nothing left of the original features.

"Stoner-inspired" is what we'll call it.....

Kind of like the DI "Kalashnikov".