British Army using Cased Telescoped Ammo

[KamenRiderBlade]

http://www.gizmag.com/british-army-40-m ... ing/42405/

Do you think we will ever replace our large caliber guns (20mm+) with Cased Telescoped Ammunition across the board?

The volume + weight savings are there + ability to carry more ammo

[arian]

No reason to do so for 25mm. 40mm ammo is big. It's very long. The telescoping design is in order to reduce the length so that you can carry more rounds. By doing so, you also need to make it fatter, however. 25mm round is already pretty small, so unless there's some need to carry more ammo, then there's no point.

[gideonic]

No reason to do so for 25mm. 40mm ammo is big. It's very long. The telescoping design is in order to reduce the length so that you can carry more rounds. By doing so, you also need to make it fatter, however. 25mm round is already pretty small, so unless there's some need to carry more ammo, then there's no point.

The ammunition is indeed bigger, but it all depends on the tradeoffs and IMO there sure are more than only the projectile weight.

The autocannon itself is actually pretty small:


It has more penetration power at 3km than the 25mm at point blank


Fragmentation comparison between a 30mm airburst round (left) and the 40mm GPR-AB:


And sure, it's fatter, but look at the way it's stored and loaded (from the side), IMO pretty neat and compact:


Relative size of 25mm vs 30mm vs 40mm CT:
http://3.bp.blogspot.com/-BL6jjxpiChc/ULbKF6Kb2RI/AAAAAAAAnaE/_gZ2fLVNkas/famille%2520munitions%25202.png

Overall you certainly need less ammo to do the same job.
More here: http://www.thinkdefence.co.uk/cased-tel ... nt-system/

[KamenRiderBlade]

If the 40mm CT canon is so small, imagine what Cased Telescope Ammo could do for all the other guns.

[arian]

gideonic, obviously a 40mm is going to have a better performance than the 25mm. The question was about making telescoping 25mm rounds, however, rather than replacing 25mm with 40mm. The US Army is already looking at bigger rounds out to 50mm.

Gotta love the marketing of the supposed threat: BMP-2 or 3 or any of their variants are nowhere near those levels of armor protection. But you need a threat to justify a new round, so why not make one up.

[collimatrix]

Hi all; long time lurker. I love this forum, and I've learned a great deal reading it. Finally, I have a chance to comment on something that I actually know about.

"Telescoped" ammunition refers to ammunition where the projectile (bullet, shell, or whatever it is you're chucking downrange) is buried in the propellant, like so:



This means that for a given length, more propellant can be packed in and the ammo is more compact for a given level of performance.

There's a big downside though; the projectile has quite a bit of inertia, and the propellant is burning very quickly. A fair amount of the propellant burns and escapes around the projectile in front of it before the projectile is accelerated into the barrel to form a seal. This means that the propellant is used much less efficiently, so cased telescoped ammunition is not actually any lighter for a given performance level than conventional ammunition. It's just more compact.

Furthermore, the propellant gas escaping past the projectile causes gas etching in the bore of the weapon, drastically reducing the life of the barrel. Where a normal barrel would be good for a few tens of thousands of rounds, a cased telescoped ammunition firing barrel would only be good for a few hundred. This DOD report has much more detail for those interested; it comes from a period when a lot of work was being done on the GAU-7, a 25mm caseless gun that was supposed to arm the F-15.

So how does the new British 40mm gun defeat these old technical bugaboos of telescoped ammo?

Well, if you look at this picture from their website:



You can see that the ammunition is not telescoped at all! Well, I guess the A3B round is. Kind of. But the rest do not have a drop of propellant in front of where the projectile seals with the case and the bore wall. This configuration is no more space efficient than conventional ammo! They're just calling it "telescoped" when it clearly isn't!

The latest LSAT experimental small arms ammo has similar construction. Earlier iterations did actually have a telescoped configuration, but no longer:



So what is the point of this stuff?

Well, for one thing, the ammunition might not be any more space efficient than conventional ammo, but the gun firing it is way smaller:



For another, the ammo does somehow manage to be smaller than 40mm bofors ammo of roughly the same performance. How? Well, it's clearly not due to a more efficient case design, so it must have to do with higher breech pressures or more advanced propellant chemistry. The 40mm is a fairly old design, so there was doubtless some room for improvement.

[KamenRiderBlade]

Would a Rebated Boat Tail on the back of the Projectile help deal with the gas escape issue out of the front?

[SpudmanWP]

Hi all; long time lurker. I love this forum, and I've learned a great deal reading it. Finally, I have a chance to comment on something that I actually know about.

I think you either read it wrong or were given old info since you seem to be way off of current demonstrated systems.

I notice that you provided a link to a DoD report from '96, but are not showing anything newer but your pic is from recent development.

For example, recent development in the LSAT program claims vs belted 5.56 ammo:
40% reduction in weight & 12% reduction in volume for Cased Telescoping Ammo
47% reduction in weight & 40% reduction in volume for Caseless Ammo



http://www.textronsystems.com/sites/def ... asheet.pdf
http://www.dtic.mil/ndia/2014armaments/ ... hipley.pdf

As far as your claim of the 40mm CTWS ammo not actually telescoping... I'd say half the length of the original is pretty good.

[garrya]

Can someone explain for me how can telescoped ammunition have equal performance with normal ammunition ? , it look like most of the propellant does not even propelled the bullet forward , only a tiny fraction of propellant do that

[SpudmanWP]

1. It's wider than the ammo it's replacing
2. CT Small arms ammo can sometimes not use "powder", but a solid propellant (ie more energy density.)
3. CT asn Caseless ammo use a three stage ignition system vs the normal 2.



Stage:
1. Primer
2. Booster. This has a very high burn rate and gets the bullet moving.
3. Main propellant, Because it was initially ignited in the area of the booster, the propellant does not burn until after the bullet has passed that part of the propellant. This way the propellant acts as a gas check/seal till the bullet enters the barrel proper.

Part 4 is the case.

Some CT cases have a solid nose where there is no need to control powder burn. This would use the standard Primer & Powder 2 stage ignition system.

[collimatrix]

Hi all; long time lurker. I love this forum, and I've learned a great deal reading it. Finally, I have a chance to comment on something that I actually know about.

I think you either read it wrong or were given old info since you seem to be way off of current demonstrated systems.

I notice that you provided a link to a DoD report from '96, but are not showing anything newer but your pic is from recent development.

For example, recent development in the LSAT program claims vs belted 5.56 ammo:
40% reduction in weight & 12% reduction in volume for Cased Telescoping Ammo
47% reduction in weight & 40% reduction in volume for Caseless Ammo



http://www.textronsystems.com/sites/def ... asheet.pdf
http://www.dtic.mil/ndia/2014armaments/ ... hipley.pdf

The small-caliber LSAT ammunition program was originally started by AAI, but now it's a joint AAI/Textron development.

When it was started there were two proposed configurations; cased telescoped and caseless telescoped.

The caseless telescoped was basically a clone of the old HK G11 ammunition. That configuration offered astounding reductions in weight and had equally astounding unsolved technical problems. Here's a presentation by someone who worked on it.

So they ditched the caseless configuration, but not before cloning the High Ignition Temperature Propellant from the old 4.92mm ammunition, as this presentation shows. That might be a clue to how they're getting the improvements in volume. The HITP was denatured hexogen, rather than the double-based nitrocellulose and nitroglycerin propellant normally used in small arms. In addition to not cooking off at elevated chamber temperatures, HITP had somewhat better energy density.

That presentation also shows this illuminating slide:



At spiral 2 the "telescoped" ammunition stops actually being telescoped! There is clearly no propellant in front of the bearing surface of the projectile! If there is no propellant in front of the projectile the ammunition is not telescoped! That's what "telescoped" means!

As far as your claim of the 40mm CTWS ammo not actually telescoping... I'd say half the length of the original is pretty good.

It's a dramatic reduction in size, but they haven't achieved it through telescoping the ammunition. I don't know what else to say besides look at the cross section. There is clearly no propellant in front of the bearing surface of the projectile!

1. It's wider than the ammo it's replacing
2. CT Small arms ammo can sometimes not use "powder", but a solid propellant (ie more energy density.)
3. CT asn Caseless ammo use a three stage ignition system vs the normal 2.

[img]<span%20class="skimlinks-unlinked">http://i.imgur.com/1T59y1c.png</span>[/img]

Stage:
1. Primer
2. Booster. This has a very high burn rate and gets the bullet moving.
3. Main propellant, Because it was initially ignited in the area of the booster, the propellant does not burn until after the bullet has passed that part of the propellant. This way the propellant acts as a gas check/seal till the bullet enters the barrel proper.

Part 4 is the case.

Some CT cases have a solid nose where there is no need to control powder burn. This would use the standard Primer & Powder 2 stage ignition system.

The booster is responsible for more than just getting the bullet going. In the Jim Schatz presentation above he explains how the booster also fractures the solid grain of the propellant. The propellant won't burn fast enough if it's all one piece because it won't have enough surface area.

Speaking of burn rates, there's no way that the bullet can get its bearing surfaces slid into the bore before the propellant in front of it burns. The burn rate of the propellant is much faster than the projectile's acceleration:



Thus the barrel throat erosion problems noted in telescoped ammunition in the DOD report above.

[SpudmanWP]

Now I understand your confusion. You're hung up on the definition of telescoped ammo. You are under the misconception that the propellent has to surround the entire bullet.

This is not the case (pun intended)

Per wiki (yeah, I know "wiki", but do you have an official source that says otherwise?)

Telescoped ammunition is an ammunition design in which the projectile is partially or completely enveloped by the propellant.

Based on any of the above pics, the propellent does indeed envelope a large portion, if not a clear majority of the projectile.

Here's the latest info (April 2016). They are are even texting a 6.5mm Carbine version... me want one
http://www.dtic.mil/ndia/2016armament/1 ... illips.pdf

[collimatrix]

I think that the manufacturers must be using wiki's definition. The problem is then, that 5.56mm MK262 open tip match ammunition is "telescoped" under that definition:



So again, them saying that their ammunition is "telescoped" does little to explain why it's so much smaller.

[SpudmanWP]

Funny, that pic show ZERO powder surrounding the projectile

All I see is air.

As a reloader, I can tell you there is often empty space at the top of the case.

Again, If you have a better, contradictory & official definition.. let me know.

I think it has a lot to do with the projectile being completely encapsulated in the case rather than completely surrounded by the propellent.

[collimatrix]

There may have been propellant around the case, and it simply fell out when the case was sectioned. Most people who have attempted to come up with MK 262 ballistics have ended up with compressed powder loads. But I believe the powder used in Mk 262 is proprietary, and last I checked Black Hills was not giving out their recipe, so I can't swear to it.

But it's irrelevant either way. You can't just get rid of the air space in a cartridge case and expect it to work. The air space is an integral part of the propellant volume. If you get rid of that space there will be less volume in the case, which means that the pressure and temperature of the propellant gas will be higher (ideal gas law). Which means that the burn rate will be higher, which will mean that more of the powder will burn before the bullet can move as far. Which means that the peak pressure within the firing chamber will be higher. Which might mean that the gun explodes, depending on what the safety margins were.

But as a reloader you already know this, so I'm curious why you brought it up.

There are three good reasons to insist that "telescoped" ammunition should mean ammunition where the propellant charge extends forward of the bearing surface of the projectile.

The first is that, historically, this is exactly what this meant. From the 1996 DOD report:

Air Force laboratory
personnel conceived the cased telescoped ammunition concept in 1954. The
cased telescoped concept places the ammunition projectile completely within the
cartridge, instead of protruding from the top of the cartridge as in conventional
ammunition.

And from this 1977 report (link opens a download):

The projectile tip
was positioned 0.1 inch from the forward end of the cartridge.

What happened was that AAI/Textron tried this old telescoped configuration, and found that it always causes unacceptable bore erosion. There is no way around this; as the graph below shows, the flame front of the deflagrating propellant outruns the movement of the projectile even in small arms calibers. In autocannons it will only be worse due to square/cube scaling.

So AAI/Textron moved the propellant backwards to provide good obturation at the case mouth... and kept calling the round "telescoped" even though it wasn't, given the (by then decades-old) understanding of what that word meant in that context.

The second reason to insist that "telescoped" ammunition only refer to configuration where the propellant extends past the bearing surface of the projectile is that if the projectile merely needs to be somewhat submerged in the propellant, then a large number of existing munitions are already "telescoped." Look how far the dart in M829A3 APFSDS extends:



But nobody calls that "telescoped".

Russian 125mm APFSDS is the same way:



Nobody calls that "telescoped" either.

The third reason to insist that "telescoped" refers only to configurations where the propellant extends past the bearing surface of the projectile is that this distinction denotes a more volumetrically efficient configuration. In the AAI/Textron and BAE/Nexter ammunition the available volume for propellant is not extended. They've just made the inert, non-energetic portion of the case bigger. If the propellant envelope is not extended past the bearing surface of the projectile, there is no additional volume freed up.

So how do they get the ammunition so much smaller than the old Bofors L70 ammo? It isn't that the CTA ammo is wider. It is in fact exactly the same diameter as Bofors L70 40mm ammo. And when firing HEAB it has about 8% more muzzle energy.