Accelerator Rifles and Beyond

[daibaka]

Sparked by a comment of Sigg Oddra's in the ACP thread, I got to thinking about the feasibility of an Accelerator Pistol. The Accelerator Rifle always struck me as an interesting weapon, but in the Traveller tech trees it seemed somewhat dead-ended and isolated. It uses a low recoil, 2 stage rocket propelled round to avoid all that nasty tumbling around in vacuum while still being an effective weapon when on the ground. Whats to stop you from using the same round in a pistol-form launch platform (which is all the rifle is, essentially)?

If you used the same round it would simplify logistics and the fact that its low velocity already rules out the main problem with using conventional rifle ammo in pistols, which is the power and recoil of the rounds. I would imagine that the round itself is quite large (in length - not sure on calibre), so the pistol would probably be closer to SMG size, but it certainly seems a likely prospect. I'm sure that this isn't an original idea, so if any of you have examples you'd like to share or arguments against feel free to wade on in!

Another thing which I just considered is some form of squad support weapon using the same round or a heavier version. Something like an LMG, perhaps. Comments?

 

[Anthony]

The main problems with accelerator weapons are that realistically, accuracy would be quite poor, and that it takes a while for the projectile to reach full velocity, meaning the weapon doesn't do full damage at short ranges. As a primary role of a pistol is short range combat, the reduced damage at short range might be a significant problem.

Given that you've solved the problems with accelerator rounds, there's no real reason to use a rifle to launch them; most rocket launchers are very short relative to their caliber.

 

[veltyen]

Hasn't this already been done?

Gyrojet pistol

Yes. Hideously inaccurate. It needs a simple laser pointer and a basic guidance system to reach the accuracy of modern firearms. For its day not a bad toy though. The other problem is speed on exit, firing at point blank is pointless. Between these two factors (no power at point blank, no accuracy at range) it is fairly easy to work out why they aren't used these days.

This possibly could be revisited for long range sniping work, in which case semi-guided bullets would be a better way to go.[1]

Another problem is that it swaps the expense arround. Instead of having a moderately expensive weapon firing cheap bullets, you have a cheap weapon firing extremely expensive (and delicate, and finicky) bullets.

[1] The other option is to use both concepts. Fire a rocket/jet based munition out of a conventional high velocity rifle. There is a weapon[2] that fires its projectile hypersonic, fast enough to ignite a small scramjet. Impact speeds over 10 km/s may be acheivable that way.

[2]http://world.guns.ru/sniper/sn46-e.htm

 

[Todg]

I think the point is that the acceleratore pistol has minimal recoil, an important factort in zero-G. Every limitation of the MBA GyroJet certainly applies. That is not to say a more workable design couldn't be made.

For long range sniping you'll need guided rounds just because of the time of flight.

As to the scramjet idea, it seems overly complicated and for little gain. High velocity projectiles of typical bullet mass won't stand up to the velocities mentioned. Scramjet bullets will have the added complexity of the jet, plus fuel.

Rail guns will be able to provide high velocities with relatively uncomplex and cheap bullets, keeping the expense right where it should be (as you note).

 

[veltyen]

Scramjets don't have any moving parts in the traditional sense, so manufacture could be quite cheap potentially. The tolerances need to be a bit higher then normal munitions (even fancy tank rounds) but otherwise they should be acheiveable. Think of it as a couple of TL's of refinement.

The thought came to me due to the fact that one of the test scramjets would have easily fit into a smallish cannon (about 40mm by memory). With stunning additional acceleration from the jet (one test reported 10000 G in flight, I suspect that was an abberant measurement) this could be a worthwhile anti-aircraft-carrier infantry carried weapon.

Railguns have a limit at arround 4km/s. Coilguns have an even lower limit. Mass drivers need a munition even more complex then a jet but doesn't have an upper speed limit as far as I know. So none of these offer a real advantage over a scramjet based munition.

The problem with scramjets is the need to be travelling at 2km/s + to start with. This can be done with conventional rifles (note "can be done" rather then "easily done"). The Steyr I mentioned being a good start. It already has a shaped high tolerance projectile, swapping that out to a sabot mounted scramjet engine isn't that far a stretch of fancy.

A additional problem in traveller is the need for an appropriate atmosphere to travel through.

It makes tanks obsolete. It would be an anti-material rifle able to punch through multiple Abrams, something modern AMR's only dream of.

My current obsession with shotguns would also bring to mind an 18.5 mm gyrojet round as an alternative load for zero-g engagements.

 

[Straybow]

Even at 5km/s an AMR round wouldn't have the mass to effect penetration of DU/Chobham type armor of notable thickness. Something akin to stand-off anti-shaped-charge plates might be sufficient to break up a hypervelocity AMR round.

To get greater mass up to 2km/s for scramjet ignition would put it out of the AMR category and into the FGMP category.

 

[veltyen]

Armour is normally rated as rolled steel equivalents.

The Abrams is normally given a rating against kinetic rounds of approximately 700mm for front armour.

The steyr round mentioned above is supposedly good for one maybe two layers of 40mm armour. It has a muzzle velocity of 1.5 km/s.

At 5 km/s the projectile has approximately 10 times the energy, and while not linear you can approximate that it should penetrate about 10 times the armour. That would be 400-800mm of equivalent armour. Or an Abrams front armour.

It isn't a shaped charge, a chemical burner, or anything else that chobham should be good for. It is purely a kinetic round, pitiful against soft targets (probably worse then a single .223 round), and fantastic against armour. Intercepting a 5km/s projectile would be an interesting exercise for any kind of active defence.

Last of all it is a purely theoretical toy. I'm not expecting anything like this to go into prototype for another 30 years, if ever. We need to crack working hypersonic scramjets first at minimum.

. TL10+ with prototypes popping up starting at high TL8.

For tanks, navy, and anti-aircraft work it may end up being a useful toy. The launch doesn't have to be chemical, it could initially see use as a weapon enhancement for naval railguns.

Assuming the acceleration figure given above is correct, and a burn time of 0.1 seconds, you would have a projectile moving at approximately 12 km/s at 700 metres range 0.1 seconds after firing. 12 km/s is meteorite strike speed.

 

[Fritz_Brown]

And, of course, the real problem with scramjet projectiles is they won't work in a vacuum - where most 0-G encounters occur (at least in Traveller).

 

[Todg]

Originally posted by veltyen:
Railguns have a limit at arround 4km/s.

The current velocity record for a railgun is 52,400 fps. or about 16k/s

The problem with scramjets is the need to be travelling at 2km/s + to start with. This can be done with conventional rifles (note "can be done" rather then "easily done").

The maximum velocity you can achieve with conventional propellants is about 4,800 fps (theoretically, you can get almost 6000fps but only in PhysicsLand) - one of the reasons first ETC and now railguns are of interest to the military.

A additional problem in traveller is the need for an appropriate atmosphere to travel through.

You also need fuel.

It makes tanks obsolete. It would be an anti-material rifle able to punch through multiple Abrams, something modern AMR's only dream of.

According to gun designers, the tank has been obsolete since shortly after it's creatiuon. Modern ATGMs were supposed to make the tank untenable as a weapon of war, and yet, we still have tanks. You have to assume tht the same technological advances in one weapon system will also occur in every other weapon.

 

[Todg]

Take a look at LOSAT. A relatively simple technology for tank killing available now. Man portable variants are in development.

 

[Todg]

Originally posted by veltyen:
At 5 km/s the projectile has approximately 10 times the energy, and while not linear you can approximate that it should penetrate about 10 times the armour. That would be 400-800mm of equivalent armour. Or an Abrams front armour.

There are a whole host of factors that effect armor penetration, velocity being only one. You can use DeMarro's formula to get penetration figures for long rod penetrators, but it is a very gross simplification:

(T*[sec(theta)^0.75]/D) - 1 = (v^2/u^2)*[(D/L)^0.3]*(M/D^3)

T = target thickness, in cm
theta = angle of obliquity
D = diameter of penetrator, in cm
v = velocity of penetrator, in m/s
u = penetrator constant
L = penetrator length, in cm
M = penetrator mass, in g

'u' is about 4 000 for heavy steel penetrators and is about 3 500 for tungsten/Du penetrators.

Note that this formula doesn't take into account the strength of the target and penetrator material as well as a number of other critical factors.

 

[Maladominus]

Originally posted by Corejob:
I think the point is that the acceleratore pistol has minimal recoil, an important factort in zero-G.

I thought that the ever-popular Snub Pistols were already favorably suitable for Zero-G environments.

At least according to canon sources, snub pistols perform very well in Zero-G environs and were a preferred shipboard weapon. I could be wrong.

 

[daibaka]

You're not wrong. I'm merely postulating alternative uses for the Accelerator Rifle technology to produce a family of weapons. It seems to me that comparisons with the gyrojet pistol of the 70's is not particularly useful, given that we are talking about 2 or 3 tech levels of development on the basic technology. It would be nice to see a Traveller version of the gyrojet for historical completeness, though.

As for the accelerator pistol, I'm of two minds. The rifle is intended for Low-G combat operations, one of the most likely of which are going to be ship boarding actions. In that kind of environment, the rifle would have to be useful at pretty close ranges, so what advantage would a longer barrel give? Greater accuracy? Or would that be inherent in the round itself? Would a pistol round need to be "cut-down" so that it exhausted its initial propellant sooner (i.e. just outside the barrel) before the second charge kicked in?

As for the ever-present snubbie, I have nothing against them at all. The accelerator weapon technology seems to me to be designed to allow similar handling characteristics (or possibly superior) in low G at longer range, while the snub round is a very low velocity "conventional" munition, albeit one of large calibre (TA1 has it at something like 18mm, I believe).

 

[Todg]

I ran the numbers for the snub pistol through my recoil calculator. Given the data from book 4 Mercenary, the snub pistol generates a recoil energy of 24J. For comparison, a S&W N frame .44 magnum revolver generates about 20J of recoil energy.

 

[mike wightman]

The Assault Rocket Launcher, a fusion of the ACR and the Accelerator rifle/snub ammo, started off as a JTAS variant.

It was canonised in MegaTraveller

 

[daibaka]

I forgot about the Assault Rocket Launcher. Never thought of it as a derivative of the ACR though. Think I'll have to dig my MT stuff out next time I'm up North and refresh my memory.

It does raise a point though. If you have the variety of rounds for the snubbie, why don't they use them for the Accelerator Rifle? That only uses a straight ball round right? Or at least as straight as a rocket propelled bullet can be. Most projectile weapons that come after the snub use a similar variety of "warheads", but the Accelerator Rifle (or at least the version in the book) doesn't. A limitation of the technology?

On the subject of hypervelocity scramjet ammo, how much use would it be? Assuming it was being used from a rifle style launch platform, it would have to be a 3 stage process surely, at least if you want to avoid problems with backblast and severe recoil? First stage would kick the round clear of the weapon (and the firer), second would then accelerate the round up to a speed where the scramjet would begin operating and begin burning its own fuel, constituting the third and final stage. How much ground would it have covered by the time it reached optimal velocity?

As for the Accelerator Pistol, I'm begining to think that it would perhaps either have to have a long barrel (for a pistol) or use a cut down version of the rifle cartridge. You could use the same propellants and same calibre ball or penetrator or whatever, but the sizes of the propellant charges would have to be shorter. I'm envisaging something like a larger calibre Mauser Broomhandle at the moment, with a longer magazine, mainly because I think it looks cool, but also because that configuration also allows for larger rounds than could easily fit in a grip-housed mag. Mainly a matter of aesthetics of course!

As for a support weapon variant (separate from the ARL), would it be worth developing? If your technology base is set up to support the production of AR's on any scale, the basic building blocks are there. You are already making the propellent, all you need to do is fit a larger calibre bullet onto it and develop a faster firing weapon. One thing which occurred to me is what would the visual signature of one of these things firing be like? Modern rockets leave quite a trail of smoke and fire behind - imagine a company of Accelerator Riflemen opening up simultaneously! At least they could leave the reflec at home, no laser could get through their smoke screen! What about if they were supported by Accelerator M2 equivalents? That would be some sound and fury!

 

[Fritz_Brown]

Originally posted by Corejob:
I ran the numbers for the snub pistol through my recoil calculator. Given the data from book 4 Mercenary, the snub pistol generates a recoil energy of 24J. For comparison, a S&W N frame .44 magnum revolver generates about 20J of recoil energy.

Yikes! Did you take into account the short barrel, Corejob? Or, are they just overestimating the punch of a pistol, in general?

daibaka, I just think an easier solution would be smart munitions dispensed by artillery or air support. These would be mini-missiles, but you don't have to redesign your infantry weapons. Though, I like the idea of a smoke-filled battlefield, with combat armor vice Redcoats coming through the smoke.

 

[Todg]

Barrel length is immaterial. Recoil energy is a funchtion of weapon mass, projectil mass, propellant mass and projectile velocity. The canon snub masses only 250g, so it's going to snap like all get out.

It's obvious that a lot of detail in Trav weren't really fully thought out if you actually look at some of the numbers.

 

[veltyen]

G'day Corejob,

I've been looking up maximum velocities for chemical powered weapons, is the figure you quote just for conventional (or near conventional) type rifles?

Oh. A prototype scramrifle exists called the SHARP

Not quite infantry carried yet

 

[Fritz_Brown]

Won't the barrel length affect how quickly the energy dissipates, though? Since it does affect muzzle velocity (to a point), right?