PRM2 said:

I really hope that as M855A1 was designed as lead free ammunition which would also improve the effectiveness of the M4,

I have recently reviewed some data on lead free ammo for military use. Which included the M855A1. Actually its the modern go to standard in this regard.

The M855A1 definetly is lead free. Completly. Not only the bullet but the primer and propellant as well. In this regard its 100 % "green".
BUT this is only a byproduct. The M855A1 has not been developed as a green bullet. It has been developed as an improvement over the M855, wich is allready apparent in its name "enhanced performance round". Since the lead free approach did not only not interfere with the goal of performance increase but actually helped this is what they chose to do.

PRM2 said:

here isn't a similar velocity dip, this time around 16 inches barrel length.

The M855A1 has been designed to give allmost the same performance from a 20" barrel from a 14.5" M4 barrel. Which it does. The difference is really small (under 30 m/s or 100 fps). A 16" barrel would be between a 14.5" and 20" barrel.

PRM2 said:

I don't think I have ever seen any actual data of M855A1 performance in longer barrel lengths than the M4.

Than you haven't really searched because there are several easily available on the internet.
The documentation of the M855A1 that is publicly available is really thorough. Including loading data and the propellant used.

Ok, point taken

Thanks for the information, the author of the article really did a great job of summarising all the issues around M855A1, despite the quaint way that the critically important velocity and chamber pressure figures had been left out of publically released official statements. When I wrote the previous question I should have explicitly referred to M995. 

My final question to the forum contributors, before I quit from derailing the discussion in this thread, is what is the current cost per round for 5.56 M995, compared to roughly $14.30 for 7.62 ADVAP and $12.37 for 6.8 SP. And I know I am being slighly unfair due to differring phases of product maturity.

PRM2 said:

My final question to the forum contributors, before I quit from derailing the discussion in this thread, is what is the current cost per round for 5.56 M995

I recall reading it was like $2-3, but thats from long memory. This was at a time when 5.56 M855 was $0.25ish or even less. 

The problem is we've seen from testing done by Buffman is the M995 even from a 22" barrel was unreliable / unable to defeat Level IV from 40' away. 7.62 M993 @ 2850fps from 40' away was also stopped by some plates. 

...

Ultimately NGSW comes down to whether armor piercing capability matters / is a primary factor in cartridge design.

If AP is key consideration, then either a magnum cartridge like 6.8 or a saboted APDS is the correct choice. 

If not then a lighter caliber makes a lot more sense.

Thank you, I suspect most people on the forum are probably of the opinion that 5.56 is good enough for most uses, except AP, and you can work around that with a Designated Marksman and/or calling in fire support.

PRM2 said:

Thank you, I suspect most people on the forum are probably of the opinion that 5.56 is good enough for most uses, except AP,

Arf, that was a point heavily debated "back in the days"...

gatnerd said:

I recall reading it was like $2-3, but thats from long memory. This was at a time when 5.56 M855 was $0.25ish or even less.

Yes, that's right.

gatnerd said:

The problem is we've seen from testing done by Buffman is the M995 even from a 22" barrel was unreliable / unable to defeat Level IV from 40' away. 7.62 M993 @ 2850fps from 40' away was also stopped by some plates.

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.

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.

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.