I need their 5.56 ammo so I can pull the bullets and load M855A1 EPRs to put in my Kel-Tec RDB so I can fight robots while my built-in cybernetic mirrored shades are deployed.

Now on commercial sale in .308 Win (to start with): https://www.thefirearmblog.com/blog/2020/01/29/shot-2020-true-velocity-and-sierra-bullets/

Some more pictures of TV .308 Win here: https://forum.cartridgecollectors.org/t/308-win-from-sierra-true-velocity-composite-cartridge-case-new-for-2020/37308

A thought crossed my mind: as I understand it, one problem with polymer versions of metal cases is that the necks have to be very thin, hence TV preferring a neckless design for their clean-sheet 6.8 mm NGSW. A alternative approach might be to design a bullet with a reduced diameter at the case mouth, so the neck can be thicker. Not sure if this would allow enough contact with the bore to keep the bullet stable, though.

You certainly can do it that way, but there's really no reason to. The TV-NGSW neckless format has superior propellant capacity and compression characteristics.

As noted, a neckless design can allow a larger powder charge for a given length cartridge, or a longer projectile with the same charge.  There have probably been designs that tried to tuck the neck backwards into a metallic cartridge body to get the same effect, but I have never seen one. 

Years ago in one of the GPC threads here, I proposed the idea of using a neckless variation of the 7.62x51 to permit the use of a longer, higher-bc bullet.  My thinking was that this would permit a reduction of propellant and recoil while still giving acceptable long-range performance.  To be honest, I was pretty proud of myself for the idea.... for maybe 24 hours.  The next day, Badcow (Emeric) posted that there was already a patent pending on the idea, but he couldn't discuss details.  Sigh.

I am curious to see how much of the bullet's tail protrudes into the propellant space of the neckless designs.  I have often read that doing so with a normal cartridge can reduce accuracy.  Maybe this reduction is too small to be an issue for a military cartridge?

eta: clarity

QuintusO said:

You certainly can do it that way, but there's really no reason to. The TV-NGSW neckless format has superior propellant capacity and compression characteristics.

For new design weapons and ammo, no argument. I was thinking in terms of ammo fired from existing guns with no chamber modifications. As I recollect, a neckless version of the 7.62 x 51 might suffer from some disadvantages, to do with the bullet needing to jump into the leade?

nincomp said:

I am curious to see how much of the bullet's tail protrudes into the propellant space of the neckless designs.  I have often read that doing so with a normal cartridge can reduce accuracy.  Maybe this reduction is too small to be an issue for a military cartridge?

There is an accuracy advantage in having no ullage (i.e. the propellant exactly fills the available space). This is because propellant burn is more consistent. I recall seeing a presentation about the .50 BMG which was found to differ in chamber pressure, MV and accuracy depending on whether the ullage was at the primer or bullet end. One of the less well-publicised advantages of polymer cases is that their wall thickness can be adjusted for each loading to ensure that there is no ullage.

The long jump to the leade is a potential issue, no doubt.  There may be a bullet design that has a high BC and good self-aligning properties, but I don't know.    Ideally, new barrels would be fitted, which would add to the expense of the project.

I was aware of ullage being a problem.  I had not heard of customizing the wall thickness to minimize void area, but it makes perfect sense.

The bullet intrusion into the propellant area is a separate issue.  Again, its effect may be so small that it is only noticed by competition shooters, but I have read about some shooters who insist that only the boat tail of the bullet should protrude past the neck.  Some do this by careful choice of bullets, others go as far as having the chamber throat cut to get the perfect geometry.  Of course, the throat will slowly change with shooting, so the optimal conditions don't last for long.  Some shooters will routinely remove a small length of the barrel's base, then recut a new chamber slightly ahead of the previous one.  Of course, eventually the barrel will get too short and be sold, discarded, or used as a very fancy stake to hold tomato plants upright. 

So essentially you're potentially proposing modern heeled bullets then?

I have a feeling that this would be somewhat incompatible and or expensive/requiring more manufacturing steps due to the way modern jacketed ammo is made. But that's just my first impression on it.

Heeled bullet illustration below.

autogun said:

A thought crossed my mind: as I understand it, one problem with polymer versions of metal cases is that the necks have to be very thin, hence TV preferring a neckless design for their clean-sheet 6.8 mm NGSW. A alternative approach might be to design a bullet with a reduced diameter at the case mouth, so the neck can be thicker. Not sure if this would allow enough contact with the bore to keep the bullet stable, though.

You mean, just like the Mle1898D bullet with a 8.15 mm shank riding in a 8.3 mm bore?

That's one option, for sure, but you're still stuck with the very short ogive length of existing military cartridge.

Another option is to use a neckless design, and have 3 "petals" around the bullet. When the bullet starts moving, the petals "open" to allow proper bullet guidance.