PRM2 said:

Perhaps we are in a static period of small increments until something world changing comes along. For me, the sighting system is the most technically interesting aspect of NGSW, rather than the high pressure cartridge which has its own set of pros and cons. There is the intriguing prospect of further developments in neckless cartridges though !!!! But that is in another discussion thread.

Still hoping for telescopic to come off age

PRM2 said:

rather than the high pressure cartridge which has its own set of pros and cons.

Increasing the pressure to 75-80 kpsi is giving you a boost of performance similar to the one achieved during the end of the 1800's with the transition from black powder to smokeless powder.

That's significant enough to reward some attention.

Do you think this is where the future of small arms development may actually go, with 6.8x51 giving confidence that it is a practical concept?

PRM2 said:

Perhaps we are in a static period of small increments until something world changing comes along.

I would say that we have indeed been in such a "static period" for the six decades since the introduction of the SCHV concept.

I would go one stage further. 

Years of gut wrenching regret about what if we'd adopted EM2 and 7 mm drive me crazy. The FN FAL was a far superior rifle design. Its only problem is that it was invented by the Belgians not by the British RSAF team (although some members were Polish). In a further blow to British prestige, the FN MAG was also a far superior machine gun design to the TADEN. 

The original 7 mm round had an unacceptably high trajectory at longer ranges. This wasn't optimised until the .280/30 appeared. By this time it was all but identical to the T65 cartridge that became 7.62 x 51 mm NATO. Given the wars we have fought since these weapons were introduced, I think we made the right and best decisions at the time about both caliber and weapons. 

Perhaps we could go to 6.8 or 6.5 mm today. But this has only recently become possible through high pressure hybrid ammunition design. This replaces 7.62 mm not 5.56 mm. 

Guardsman26 said:

The original 7 mm round had an unacceptably high trajectory at longer ranges. This wasn't optimised until the .280/30 appeared. By this time it was all but identical to the T65 cartridge that became 7.62 x 51 mm NATO. Given the wars we have fought since these weapons were introduced, I think we made the right and best decisions at the time about both caliber and weapons.

Totally agree.

Guardsman26 said:

[6.8 mm] replaces 7.62 mm not 5.56 mm.

Huh???  Everything published to date says that 6.8 mm replaces 5.56 mm.

EmericD said:

The "ADVAP / 6.8 mm SP" generation of AP ammo seems to deliver pretty extreme capability, just like the "Stiletto" rounds developped in the UK by Ukrainian designers (that worked previously on the Russian 7N27 and 7N39 rounds if I don't mix the names). The M993 was capable of defeating 18 mm of RHA at 100 m. The DM151 is capable of defeating 16 mm of RHA at 200 m, from a shorter barrel. The "6.5 mm SP" for the Hybrid case Creedmoor could defeat 20 mm of RHA at 300+ m, so better performance than a .50 BMG AP round.

That's great info and an incredible increase in performance over M993. 

I imagine they solved the tungsten shattering issue we saw from M993 vs ceramic?

Stiletto had used a very long tungsten penetrator, whereas early pics of the 7.62 ADVAP showed a EPR style construction, where the penetrator is only ~1/2 the length of the bullet. Have they switched to a full length core, or figured out a way to make the base/slug of the ADVAP EPR add to the penetration?

From 2018:

When they originally started work on M855A1, lead-free was the main goal. Then the decision was made since they were working on a new bullet, increase the terminal performance. 

PRM2 said:

Do you think this is where the future of small arms development may actually go, with 6.8x51 giving confidence that it is a practical concept?

I worked in the hypersonic field before, and the mantra was that "hypersonic is the future of aviation, and always will be!", so I won't bet all my money on that, but...

The gains offered by running at much higher chamber Maximum Average Pressure are so significant that SIG, Federal and others are really working hard on this subject.

For the end user, that's the possibility to launch a 140 gr class bullet at 3000 fps from a 6.5 mm Creedmoor weapon, allowing 338 Lapua Magnum hit probability up to 1400 m from a compact, sub 4 kg rifle, or a 102 gr GP at 3550 fps and defeat some significant armor (you have similar gains wih the 5.56 mm or the 7.62 mm NATO).

For the manufacturers, that's the opportunity to replace all existing small arms with variants that could handle the increased pressure, and increase the cost of ammo.

That's a path the Russians started with their 6 mm "Unified", we just need someone to make the first step and others will follow.

EmericD said:

102 gr GP at 3550 fps

What barrel length would this be? And at what pressure?