Alternative to 6.5 Grendel?

[Trooper]

The problem with holding down COL to a minimum is that you are liable to end up without enough space to load long-ogive bullets. This problem affects the 5.56x45, 7.62x51 and even the .338 Lapua Magnum (which is why the .338 Norma Magnum was developed). This won't matter in short-range weapons but it surely does if you want a decent long-range performance.

Thus a 6.5x45 would do well as a replacement for both the 5.56x45 and 7.62x51. And then use the 8.59x64 (.338NM) in the med MG to replace the .50 cal M2.

Most of the troops would not need a long range weapon (20 inch barrel for the DM) and would only use 16" carbine. But a 6.5x45 would give the penetration at close quarters that the 5.56x45 does not have. The 5.56NATO is just too light to go against brick or stone buildings. Russians found that out with the 5.45x39 in Chechnya.

[Tony Williams]

Thus a 6.5x45 would do well as a replacement for both the 5.56x45 and 7.62x51. And then use the 8.59x64 (.338NM) in the med MG to replace the .50 cal M2.

Most of the troops would not need a long range weapon (20 inch barrel for the DM) and would only use 16" carbine. But a 6.5x45 would give the penetration at close quarters that the 5.56x45 does not have. The 5.56NATO is just too light to go against brick or stone buildings. Russians found that out with the 5.45x39 in Chechnya.

Quite so. The point about long-ogive bullets is that they provide long-range performance for free. Just compare the 6.8mm Rem SPC with the 6.5mm Grendel: they are about the same size and weight, and develop about the same muzzle energy and recoil, but the Grendel has been designed to take long-ogive bullets while the SPC cannot. As a result, the Grendel is a good long-range cartridge while the SPC is limited to medium range only.

[JASmith]

One of the elephants in this room is the increasing availability of lightweight body armor.

The plates in that armor are designed to defeat low to moderate velocity projectiles of average mass. We should address what additional armor-defeat features, if any, should be considered for this alternative cartridge.

For example, a sabot-launched projectile might allow an increase of, say, 300 meters per second to the muzzle velocity. That increased velocity coupled with appropriate projectile design might be good medicine for current technology body armor.

[Tony Williams]

Very true. There are of course already SLAP rounds with tungsten penetrators developed in 7.62x51 - one version has seen Swedish service in sniper rifles - and I even have a saboted 5.56mm round in my collection (although I have no idea how effective it would be!).

There might be some implications for rifling twist selection, I'm not sure.

[JASmith]

Going with dense, hard metals helps a lot for both effectiveness and keeping the length short and demands on twist rate within reason.

Here is an example that many of us have probably looked at over the last couple of years. This could be implemented in a 6.5 caliber rifle cartridge with, perhaps, a sightly longer and larger diameter sliver, but still with impressive velocities:

http://www.gotavapen.se/gota/cbj/cbj_crtg.htm

I've done the math, and that tiny tungsten sliver indeed has a very similar momentum density to that of the 7.62x51 ball round, but is a lot harder. The added strength helps explain why it does a tad better.

[stanc]

Thus a 6.5x45 would do well as a replacement for both the 5.56x45 and 7.62x51.

Most of the troops would not need a long range weapon (20 inch barrel for the DM) and would only use 16" carbine.

Correction: 16-inch barrel for the DMR, 12-inch barrel for the carbine.

[Variable]

Very true. There are of course already SLAP rounds with tungsten penetrators developed in 7.62x51 - one version has seen Swedish service in sniper rifles - and I even have a saboted 5.56mm round in my collection (although I have no idea how effective it would be!).

There might be some implications for rifling twist selection, I'm not sure.

Any accuracy info on the sabo sniper ammo? Not saying it couldn't somehow be made accurate, but my past experience was very poor.

[LRRPF52]

Projectile separation from sabots is inconsistent, so accuracy goes to crap. For close range armor piercing, it's great if you can reach .22-250 velocities.

[JASmith]

Projectile separation from sabots is inconsistent, so accuracy goes to crap. For close range armor piercing, it's great if you can reach .22-250 velocities.

The inconsistency is probably a result of separating the sabot from a spinning projectile.

Consider the M-1 Abrams tank gun. That is a sabot round and extraordinarily accurate by most of our standards.

Of course it is a smoothbore but one could speculate a scaled down smoothbore might be interesting with respect to the accuracy needs of the average infantryman.

The fly in the ointment may be the length of barrel needed to edge above 3,500 - 4,000 fps.

[Tony Williams]

Any accuracy info on the sabo sniper ammo? Not saying it couldn't somehow be made accurate, but my past experience was very poor.

Dispersion is greater, but in compensation the trajectory is flatter and the flight time shorter. How these two factors work out I really don't know, but I suspect that the sabot round would be better against fleeting or moving targets because of the short flight time.

[SHORT-N-SASSY]

Gentlemen,

This friendly discussion on Discarding Sabot ammunition prompted me to seek out some old files and revisit a favorite chapter of my life. The following is a page from that chapter. Thanks for the fond memories.

[Tony Williams]

Thanks for posting that - much better accuracy than I would have expected!

[JASmith]

Thanks S&S!

Even allowing for the inevitable drop in accuracy between commercial and "lowest bidder" military ammunition, it would seem the stuff might be good to 3 MOA in the infantry carbine. Hence the tungsten sliver might work for CQB when the adversary wears armor.

Of course, other issues need to be explored, including lethality on unarmored targets, expense and long range performance plus others not immediately remembered.

[nincomp]

The E. Arthur Brown Company (eabco.com) sells sabots for .224 bullets in 30 cal cartridges. They also have loading info.

http://eabco.com/Reports/report04.html

eta: About 10 years ago, I contacted the company that makes the sabots and asked if he made 7mm->.224 or 6.5mm->.224 sabots. At that time he said that he didn't have any demand for them, so he never tried.

[JASmith]

The E. Arthur Brown Company (eabco.com) sells sabots for .224 bullets in 30 cal cartridges. They also have loading info.
http://eabco.com/Reports/report04.html

So, we can start with the M-1 Carbine, and then work our way up in case size until an interesting velocity is reached. Off the top of my head, the Whisper may be very interesting if one can't get enough from the straight-wall carbine case.