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Military Guns and Ammunition

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This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons, particularly in larger calibres (12.7+mm).

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True Velocity polymer case ammo   Ammunition <20mm

Started 17/11/17 by gatnerd; 7960 views.
In reply toRe: msg 22
autogun

From: autogun

16-Sep

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.

QuintusO

From: QuintusO

16-Sep

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.

nincomp

From: nincomp

16-Sep

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

  • Edited 16 September 2020 14:08  by  nincomp
autogun

From: autogun

16-Sep

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?

autogun

From: autogun

16-Sep

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.

nincomp

From: nincomp

16-Sep

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. 

 

roguetechie

From: roguetechie

16-Sep

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.

EmericD

From: EmericD

16-Sep

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. 

Red7272

From: Red7272

17-Sep

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?

Short necks are no different to long necks. The longer necks are just mechanically stronger and support the projectile better. With the polymer neckless case, the projectile is welded to the case so that isn't an issue. It will allow the the flat body of the projectile to be smaller or even allow a more coke bottle shaped projectile which will will reduce friction in the bore and drag.

nincomp said:

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. 

It's theoretically possible but would make filling the case problematic, and while it might tension correctly the external neck is much more accessible for testing and correcting errors. 

autogun

From: autogun

17-Sep

EmericD said:

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.

Sure - but I was only trying to solve one potential problem without needing to alter the guns: the weakness of thin polymer necks. I wonder how the 7.62mm TV holds up when being hammered through a high-rof MG?

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