The Ultimate Combat Round

[GunTech]

Interesting groovski

I came up with a 6.5x45 independently, so Tony got it right

This round, based on the 7.62x45 Czech is just about half way between the 5.56x45 and 7.62x51 in every respect: Energy, recoil, etc.

 

[PercyShelley]

Percy, how do you intend to make the chamber spherical?

Hydrazine and HAN are both liquids. The propellants would need to be injected in a manner similar to a car engine cylinder, but chamber geometry from there is up to your imagination since it can essentially be a closed tube, excepting the action to bring the bullets in, the propellant injection system the ignition mechanism, and the muzzle.

You would need a reasonably clever system to ensure good sealing, as the propellant gases would be rather hotter and of smaller molecular weight (which is half the point of the exercise) than usual. The advantages are enormous, however.

The propellant could be stored in a tank of any geometry. Bullets, rather than cartridges would be stored in the magazine meaning a much higher density of rounds for a given length magazine. The advantages are similar to those of caseless ammunition, except without the bothers of ammunition integrity, and offering potentially higher propellant energy densities.

I would load the bullets into a mechanism similar to an aircraft revolver cannon, and slide the revolving cylinder backwards to seal it up against the chamber; perhaps with a system similar to that in the Nagant revolver. To fire, squeeze the trigger, which releases a sear connected to a spring-loaded syringe-pump which takes a consistent amount of propellant into the chamber. A catalyst in the chamber could cause the propellant to detonate or, if this is deemed insufficiently safe, ignition could proceed by electric spark.

Hydrazine is used to keep com satellites on station, start the engines in F-16s and powered the ME-163. It's not a widely used technology, but it's consistent enough to be used IN SPACE after years and years of bombardment by solar radiation, micrometeors and who knows what else. It's nasty, nasty stuff, but it works every time.

Alternatively, HAN propellants could be used. There is less industry experience with those, but they're generally more benign, slightly more powerful, and I think, no less reliable.

 

[Tony Williams]

I came up with a 6.5x45 independently, so Tony got it right

What never fails to amaze me is whenever people who understand the subject take a clean-sheet approach to the design of the best compromise military rifle/MG round, they come up with something like this - but no army ever adopts it!

 

[hags]

It's already on the market..........

 

[Grendelizer]

What never fails to amaze me is whenever people who understand the subject take a clean-sheet approach to the design of the best compromise military rifle/MG round, they come up with something like this - but no army ever adopts it!

Never were truer words spoken, er, written!

John

 

[HorseSoldier]

I would load the bullets into a mechanism similar to an aircraft revolver cannon, and slide the revolving cylinder backwards to seal it up against the chamber; perhaps with a system similar to that in the Nagant revolver. To fire, squeeze the trigger, which releases a sear connected to a spring-loaded syringe-pump which takes a consistent amount of propellant into the chamber. A catalyst in the chamber could cause the propellant to detonate or, if this is deemed insufficiently safe, ignition could proceed by electric spark.

So it's kind of like the various proposals for binary propellant cannons?

If so, I'd think that if you could make the system reliable, there might be some utility in being able to vary your muzzle velocity by adjusting the amount of propellant used. Like being able to go from assault rifle kind of power levels to something more like a battle rifle if you do find yourself having to engage soft skin or light armored vehicles, targets behind cover, etc., and then switch back to the negligible recoil, faster handling assault rifle round without even having to change magazines.

 

[Tony Williams]

So it's kind of like the various proposals for binary propellant cannons?

I really don't think that armies would want their soldiers carrying weapons filled with dangerous liquid (and presumably reload containers also). That is one consideration which has helped to kill liquid gun propellants up to now.

 

[Jeff White]

The (now canceled) Crusader 155mm howitzer was originally supposed to use a liquid propellant. They couldn't get it to work on a large scale like that. I don't think we're anywhere near ready to put it in a rifle.

Jeff

 

[Nolo]

I've been to http://www.quarry.nildram.co.uk/Assault.htm before.
The problem I have with the 6.5ers is the velocity. It just seems too low for me.
I'm looking for a given energy (~1500 ft-lbs) and a certain velocity (~2800 f/s) and with streamlined bullets that comes out to a .22 caliber projectile. Not only is that projectile unstable, it retains frangibility at long ranges and has a very flat trajectory. I think that makes for a weapon that is accurate, powerful and doesn't require diddling with to keep consistent accuracy.
I honestly think that the 5.56 bullets are a better choice than the 6.5 bullets, but I am no expert on this subject and my operational concept is probably quite a bit different.

 

[Tony Williams]

I honestly think that the 5.56 bullets are a better choice than the 6.5 bullets, but I am no expert on this subject and my operational concept is probably quite a bit different.

Othe things being equal, bigger bullets are less affected by wind than small ones. They also tend to be better at punching through walls and other cover, and make bigger holes (and hit with more momentum).

To achieve a given muzzle energy, smaller calibres need more propellant and thus larger cases.

Note that at one time the US Army wanted to replace a lot more of the 7.62x51 MGs with the 5.56mm M249, since the M855 loading is still (on paper) effective to 800m (it will still punch through a standard helmet at that range). But they had to backtrack because the little cartridge couldn't do the job. Similarly, SOCOM has acquired the lightweight Mk 48 MG - effectively a 7.62x51 Minimi (and, of course, they also want a 7.62x51 version of their new SCAR rifle). The Chinese army are finding the same thing with their new 5.8mm GPMG - this was intended to replace the 7.62x54R MGs, but they're not happy with that.

 

[Evil Monkey]

I've said this before already, the biggest problem with the military (at least the US) is that they want all the organic individual weapons and some inorganic crew-served weapons to use the same round. That is a very hard thing to do.

Like the Chinese, it's alright to use 5.8mm as an assault rifle, LMG, and marksman rifle cartridge. It's NOT OK to use it also as a long range GPMG cartridge. The round, like 5.56mm, is not as capable as the larger full power rounds. You wouldn't use the 5.56mm as a 600+ meters sniper rifle, why would you use a crew served GPMG as such?

As mush as I am a fan of logistic simplification, sometimes I feel that it's way over blown. Leave one cartridge for organic weapons, and one for inorganic weapons.

On the subject of SOF's, they require appropriate weaponry for each of their missions. Meaning, one day it's an M4, another day it's an M14. A huge military needs weapons that are versatile for a variety of missions. One for all, and all for one. The "Ultimate Combat Round" has little to no effect on SOF operations.

 

[Jorg Nysgerrig]

individual weapons and some inorganic crew-served weapons to use the same round. That is a very hard thing to do.

Would you mind explaning the difference between organic and inorganic military weapons the context of your post?

 

[Nolo]

I agree with Evil Monkey, I think that you should have two cartridges.
My idea?
A 5.56mm cartridge, just like the 5.56 Lambda.
A 10mm cartridge, just like the .408 CheyTac.
Maybe smaller than 10mm.
I don't know.
But I think the disparity should be pretty big.

 

[Nolo]

I get it, Jorg, he's talking about the difference between someone's rifle and something like a SAW that is more like an artillery piece.

 

[Evil Monkey]

Would you mind explaning the difference between organic and inorganic military weaposn the context of your post?

Based on what I've learned so far, I believe organic weapons are the weapons used in the immediate squads in the platoon. These are the individual weapons like the assault rifle, marksman rifle, SAW, grenade launcher, disposable or reusable rocket launcher.

I believe the inorganic weapons are the crew served weapons in combat support. These would be the GPMG and its team, mortar, sniper teams (sniper rifle itself), HMG, GMG, etc. These weapons require a team to operate efficiently and are used for the most part to support the infantry. The fact that most or all of these teams are not attached to fireteams or squads make their weapons inorganic.

You can have a GPMG team in the light role attached to a squad, but does that make the team and GPMG organic or not? Some say yes, some no.

Reminds of something I read not too long ago about how Russian special forces wanted an "organic" machine gun, so they put a PKM in the squad. Whether it was used as an individual or crew served weapon was not mentioned.

 

[Grendelizer]

I've said this before already, the biggest problem with the military (at least the US) is that they want all the organic individual weapons and some inorganic crew-served weapons to use the same round. That is a very hard thing to do.

Like the Chinese, it's alright to use 5.8mm as an assault rifle, LMG, and marksman rifle cartridge. It's NOT OK to use it also as a long range GPMG cartridge. The round, like 5.56mm, is not as capable as the larger full power rounds. You wouldn't use the 5.56mm as a 600+ meters sniper rifle, why would you use a crew served GPMG as such?

Evil, would your opinion change if the "unified cartridge," while as compact as an assault rifle cartridge, delivered much of the capability of the GPMG cartridge?

Consider the attached graphs:

If not the 6.5 Grendel, then maybe the 6.5x45 mentioned above. At any rate, I think it's pretty close to the ultimate combat round. What criticisms, if any, might you have of the 6.5 Grendel's performance shown above?

If Jeff White is still out there, I'd also particularly like his input, because he's opinionated, smart, and (if I remember) military experienced.

John

 

[Deer Hunter]

Grendelizer, the one thing I dislike about those graphs are the horrible bias against the 7.62 NATO. Every other round is state-of-the-art with the best bullet loaded to a great pressure standard. Hell, even the old 7.62x39 gets a facelift. But the 7.62 NATO stays roughly untouched. Stick new bullets in it and pump the FPS to 2800 fps and then make the graph.

 

[Evil Monkey]

What criticisms, if any, might you have of the 6.5 Grendel's performance shown above?

If what the graphs show are realistic, then I have no criticisms for the grendel.

In my opinion, I think what we have is perfectly fine. We have the 5.56mm for all individual weapons and the 7.62mm for specialized weapons (think GPMG and sniper rifles).

 

[PercyShelley]

So it's kind of like the various proposals for binary propellant cannons?

If so, I'd think that if you could make the system reliable, there might be some utility in being able to vary your muzzle velocity by adjusting the amount of propellant used. Like being able to go from assault rifle kind of power levels to something more like a battle rifle if you do find yourself having to engage soft skin or light armored vehicles, targets behind cover, etc., and then switch back to the negligible recoil, faster handling assault rifle round without even having to change magazines.

Yes, except you only have to fool with one chemical. It loses a bit of power compared to some of the more exotic bipropellant combinations, but it's less fiddly.

Good point about the variable power.

Aside from the crusader (the liquid propellant prototypes of which used regenerative HAN propellant-cannons IIRC), I seem to recall the Navy fooling about with liquid propellants as well. I don't think anything's exceeded prototype stages yet, but it's clearly a physical possibility. At this point it's rather like master gunsmiths fooling around with multi-shot and breech loading weapons in the 1700s; we're waiting for the manufacturing technology, industry experience and thinking to catch up.

 

[GunTech]

People need to go back and read this whole thread. Deer Hunter brought up and issue with the 6.5 Grendel that was discussed early on. Alexander Arms slants their data to heavily favor the 6.5 grendel.

The forst thing you have to do is throw out the SMK as a combat round. It lacks adequate barrier penetration, is probably questionable per the Hague conventions and lack a canneleur and crimped bullet that is universal for modern military rounds. Some studies suggest it is inappropriate for belt fed weapons. Body taper and shoulder angle are certainly not optimal for automatic weapons.

The grendel is a excellent concept limited by the requirement that it fit in existing weapons.

Clean sheet of paper designs like the 6.5 described previously address the failings of the Grendel, having better case taper and profiles more suited to automatic weapons, while at the same time exceeding the grendel's ballistics while operating at much more models pressures.

I have been shooting Grendel for over a while, and I have yet to duplicate the most optimistic ballistics published by AA.

The grendel is a great round, but it is not the wonder round some seem to think it is. For example, compare penetration of Grendel to M80 ball against mild steel plates, or even wood barriers.

 

[GunTech]

PercyShelly,

I'm now wondering of you've read liquid propellant gun technology by Klimgenberg et al

 

[GunTech]

Grendelizer, a couple on nits on your chart.

The velocity of M80 ball used for comparison with 6.5 grendel is listed at 2600 fps. This is incorrect. Spec velocity for M80 ball is 2750 fps. Can you explain the discrepancy? That's a difference of 150 fps.

 

[Grendelizer]

Deer Hunter and GunTech: Please note that all velocities are from 16" barrels, including the 7.62 M80.

I usually compare the 6.5 Grendel to 7.62 NATO M118LR with its 175gr Sierra MatchKing. Thus, I usually end up comparing Black Hills Ammunition 6.5 Grendel 123 SMK to Black Hills 7.62 M118LR with a 175 SMK. If that isn't the closest to an apples-to-apples comparison, I don't know what is. By the way, 6.5 Grendel still performs very well in that comparison.

In this particular graph, where I was using 16" barrels, I thought it was more likely that M80 would be found in 16" barrels, such as the newer Mk48 machine gun, rather than M118LR, which would more usually be found in longer sniper barrels. But, as I've said, 6.5 Grendel will go toe-to-toe with M118LR in any barrel length you choose.

As always, it is not my contention that 6.5 Grendel blows 7.62 NATO "out of the water," but that it is unique in giving very close to 7.62 NATO performance from handier weapons and with half the recoil.

In other notes, I won't grant Tod any "shoulder angle" or "body taper" disadvantages to the Grendel.

I will grant Tod some theoretical penetration advantages in very specific materials, such as concrete, for M80 due to its increased mass. But this would need to be thoroughly tested and a military 6.5mm FMJ would need to be developed, which, with a very nice sectional density, probably wouldn't be a slouch in the penetration department, either.

John

 

[GunTech]

There are a couple of 'military' 6.5 bullets out there, as the 6.5 has a long history as a military cartridge (since at least 1896).

The best (highest BC) FMJ for the 6.5 I know of is the Lapua 144gn FMJBT with an insane BC of 0.636. However, velocity of such a bullet from a 16 inch barrel would be relatively low.

I'm curious to know what load you are using to drive a 123 SMK at 2475 from a 16 inch bbl and what chamber pressure is? I can get that velocity from my 18 inch bbl CZ-527 Grendel using 28.5gn W748. That should be right at around 55,000 PSI, the maximum recommended pressure for an AR.

The best velocity given for the 6.5 Grendel and 123 SMK, from Alexander Arms own loading data, is 2630 from a 24 inch barrel with 30.8gn 2520. This load, fired in my Grendel resulted in flat primers and high pressure signs. It does not look like an AR15 safe loading.

Running the number though quickload, that comes up with a 108% loading density and a calculated peak pressure of around 65,000 PSI - my cases show a volume of about 36gns of water.

I just want to understand you have confirmed these velocities personally, and aren't using AA data, which in my experience, is 'optimistic'.

I started out as a huge fan of 6.5G, but actual experience with the round caused me to reassess AA's claims.

 

[GunTech]

BTW, M80 ball from my 16 inch BBL SOCOM ran about 2550 fps.