This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.
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G&A has now put online their previous print story of the TV Bullpup and 6.8 ammo. While no longer relevant for NGSW, its a fantastic article on the system:
This is an interesting write-up, I didn't pay any attention to the exact details of the SAAMI chamber designs, not thinking much about it. But you're right that there's a significant difference in the amount of freebore between the designs. Good catch. I figure GD trying to 'double dip' with their basic rifle design as both a rifle and automatic rifle with interchangeable parts is the root of that. Like you wrote up, it helps with reliability at the cost of accuracy. Which is something that you'd do with an automatic rifle.
Mix the funky freebore with a barrel that is not fixed into the action, and that chunky gas system and you could have a lot of barrel whip going on. This is entirely speculation however. The GD engineers behind the initial design weren't dumb enough to miss most of this.
>G&A tested a commercial-version of the 6.8 TVC ammunition — machine-turned, 135-grain, all-copper projectile — flash signature was virtually non-existent when the barrel was fitted with a Delta P Design suppressor.
>During bench testing, I often printed three out of five shots in a single ragged hole, but two shots strayed outside of a 1 MOA circle.
So it was around a 2 MOA gun with a solid copper bullet off of probably a cold barrel . And assumedly a at least somewhat more than that with the more internally complicated military projectiles. Decent accuracy for a combat rifle, but I could see how with this silly '800 yard point target engagement' concept the Army was pursuing, that wouldn't be desirable.
I did my analysis on the high-BC EPR-style bullet before I saw the SIG rendering and had originally planned to use the photo that Stan posted. The SIG rendering is just a worse example.
I wonder if the contestants had many of the actual Army projectiles with which to perform experiments before their designs were finalized. Depending upon the exact composition and shape of the official General Purpose Projectiles, there are any number of pertinent characteristics that might be difficult to duplicate. It would not surprise me if the developers were surprised when they saw the results of the trial.
There must be some explanation behind the odd chamber used by GD, and I suspect that it may have something to do with the neckless polymer round. The relatively large "forcing cone" would imply some issue having to do with alignment of the bullet as it is being chambered. The forces on the cartridge as it is stripped from a magazine and fed into a the chamber may come into play here. I would expect some flexing. After all, TV's cartridge is a plastic tube with metal weights at both ends.
The ogive of the 6.8 mm GP is much longer than the SMK (in both actual dimensions, and proportionally to the bullet length)...
The boat-tail is also significantly longer.
Thanks, Emeric. Can you post ogive, shank, and boattail lengths of both bullets? It seems like if those dimensions are "much" and "significantly" longer, it would be quite noticeable. But, in comparing the photos, I do not see a discernible difference in lengths of those features. They look pretty much the same to my eye.
I don't have a problem with the infantry having organic small arms for fights at 600+ meters. IFV support may not always be available.
However, I agree with the author that there is no need to penetrate body armor at 600 meters, that 100-200 meters would be enough.
But, I do not get the fascination in this forum with neckless ammo. The appeal of polymer cases is understandable, but why neckless?
Increases ogive space substantially for a given OAL, and with seemingly (until now) no downsides
And yet, both of these have 51mm case lengths, loaded with the same bullet.
The first discussion on this forum (that I recall, at least) about neckless cartridges was on a GPC thread over a decade ago. It was about using bullets with a much longer ogive and BC in a (possibly) modified 7.62x51 weapon. The goal was to retain the energy of the M80 cartridge at long range and reducing recoil GPC levels. Energy at 800 and 1000m was a big deal on this forum at the time. The quest for a neckless 5.56 cartridge is mainly about utilizing lower-drag bullets.
For the 6.8mm cartridges submitted for the NGSW trials, case design was not specified so the competitors were allow to optimize as they saw fit. Presumably, the neckless case submitted by True Velocity is optimized for the properties of the polymer. The very fact that GD/TV did not use a conventional case and neck design implies that there was something to gain.
We do not know the thought process that led to TV's submission. Maintaining current chamber pressure levels seems to have been a priority. That is one reason why I want to see TV demonstrate a polymer cartridge at higher pressures. It is a "put your money where your mouth is" moment for them.