My idea to make guns/artillery pieces easier (cheaper?) to build(a rifling rig is extremly expensive): Instead of using smooth bullets in a rifled barrel, put rounds with rifled grooves ground into the bullet in a smoothbore weapon. The grooves would be about 0.5-1mm deep. I assume the grooves would stabilize the bullet in flight through air friction in the grooves. Also, large artillery pieces need to have their barrel exchanged every 5000 shots or so, as the rifling gets worn away. With this, that wouldn't be needed, as the rifled part is replaced every time you reload. The range might be a bit less, due to the added air friction on the bullet, or does that happen with normal rifle ammo to? I assume this would make it impossible to trace bullets to specific guns, so bullet serial numbers might be a good idea.
-- Aegis, Mar 30 2004

(?) Rifled slugs http://www.ballisti...lug/Slugs/slugs.htm
There are special rifled barrels for shotguns but most shotgun slugs are rifled for use in smoothbores. [bristolz, Oct 17 2004]

(?) Ammunition types with small photos http://matrix.dumps...basics/bullets.html
Rifled slug and sabot are pictured at the very bottom of the page. [bristolz, Oct 17 2004]

Gyrojet http://en.wikipedia.org/wiki/Gyrojet
A spectacular example of why making cheaper guns with more expensive ammo tends to fail. [ye_river_xiv, Nov 02 2008]

Flu-Flus http://tradgang.com/flu-flu/
Spiral projectile for archery [csea, Nov 03 2008]

Spiral-grooved Arrow Shaft http://www.faqs.org...nts/app/20080207362
another approach [csea, Nov 03 2008]

Well, the purpose of rifling is to spin the bullet. That won't happen with your bullets and a smooth bore, and besides, all the hot gasses will escape, and the slug will just fall out the end.

(Gosh, looking at bristolz's link, I'm completely wrong.)
-- ldischler, Mar 30 2004


While this does offer an improvement to the flight characteristics of a slug fired from a smoothbore, it doesn't approach the efficiency and accuracy of a slug fired from a rifled bore.

The design of the slugs in [bristolz] first link will spin up the slug after it leaves the muzzle, hopefully before it has a chance to tumble in flight. The slug still exits the muzzle with no rotation.

Also, rifling a barrel is a one-time expense, and is consistent from shot to shot. Rifling the projectile will have much greater shot-to-shot variation.

Good idea, but with limited applications. If it wasn't so baked, I'd bun it.
-- Freefall, Mar 30 2004


[FF] I don't see the difference between rifling the barrel and rifling the bullet. Can't you have the same surface area and pattern of contact? Sure, the bullet will have different interaction with the air after leaving the barrel, but it seems to me that the interaction with the barrel should be similar.

(after a bit of research on how rifling works) Ok, it turns out that the soft lead bullet actually deforms into the rifling. This can't be done the other way.

Though perhaps the answer is to keep rifling, but add harder metal curved pieces to the bullet designed to slide into rifling. You'd have to re-engineer your gun (to have a constant rifling curve and to load the bullet correctly), but you may have to re-rifle less often.
-- Worldgineer, Mar 30 2004


I think you all would be surprised at how effective rifled slugs are. They are a favorite of deer and big game hunters and can make over 1700fps with a lot of accuracy and incredible energy. There are slug barrels available for shotguns that have light rifling in them to aid in stabilizing slugs but smoothbore with rifled slugs are quite effective. Most slug hunters sight in at about 75 to 100yds but 200 yd shots are not uncommon. I can remember that various gun/slug combinations had to be tested to find the right match between the two as accuracy varied from combination to combination. My father has a 16ga smoothbore that has felled a lot of deer with rifled slugs. (I grew up in a family of avid hunters and am somewhat steeped in the lingo of firearms. Not a great fan of them, or of hunting [especially] except for good airguns which I think are kind of fun to shoot.)

So, does my knowing about rifled slugs make this widely-know-to-exist or am I just a weirdo?
-- bristolz, Mar 30 2004


I think known-to-exist-by-[bristolz] would be a terribly stringent standard.
-- Worldgineer, Mar 30 2004


AFAIK, the rifling curve is constant (how many twists per unit length of barrel). Inside the barrel, it doesn't really matter what your bullet is shaped like.

As an analogy, consider a car driving on a wet road. If you turn the steering wheel and lock your brakes, the car continues to skid straight ahead (assuming it wasn't already spinning), despite the fact that the front wheels are angled. The same thing happens inside a smoothbore gun.

A normal bullet is a rotational solid, i.e. it has full rotational symmetry. It doesn't matter how you twist it, it will fit in the breech the same way. As the bullet leaves the cartridge, it's forced across the rifling lands and grooves, and the surface of the bullet becomes as an exact fit to the inner surface of the barrel. The bullet spins with the rifling just as a train moves along its tracks.

Making a bullet to custom-fit your rifling will require more complex bullet manufacturing processes and much more precise placement of a cartridge in the breech. This will make any type of repeating firearm (aside from possibly a revolver type) much more complex.

I stated earlier that the rifled slugs (as used in shotguns; I've used them myself on occasion) are effective in a limited scenario (using a slug in a smoothbore gun otherwise designed for shot), providing increased range and accuracy and a flatter trajectory than an unrifled slug that is allowed to tumble. Shots out to 200 yards are made possible by the use of this type of slug in a shotgun. For a quality rifle in the hands of a good marksman, 200 yards is laughably short range. 500 yards starts to get interesting, 750 is a challenge and 1000+ gets difficult. (A family friend is a retired sniper. He used the standard issue rifles while he was active, but in retirement, he uses a custom made gun with 30.06 cartridges that he necks down to .223, shooting .2 moa. (a quarter at 1000 yds is approximately 1 moa)). To do this, consistency is absolutely critical.

I stand by my statement; rifling the slug will provide an improvement over an unrifled slug in a very limited set of conditions, so in general, (+). But, since rifled slugs already exist, I stand by my [mfd].
-- Freefall, Mar 30 2004


What mfd?
-- bristolz, Mar 30 2004


// (a quarter at 1000 yds is approximately 1 moa) // I think your '0' key stuttered there, [Freefall]. 1 less zero would be about right.
-- lurch, Mar 30 2004


Ah, so I did...I stand corrected.
-- Freefall, Mar 30 2004


//Ok, it turns out that the soft lead bullet actually deforms into the rifling. This can't be done the other way.//

Maybe if you made rifled steel bullets, and put a new lead sheath inside the barrel after each shot...
-- ye_river_xiv, Nov 02 2008


how about the propellant putting a spin on the slug
-- FlyingToaster, Nov 03 2008


//how about the propellant putting a spin on the slug//
That's what Gyrojet did, isn't it?
-- coprocephalous, Nov 03 2008


//their conservatism stopped the project//
That and the fact that you could stop the round leaving the barrel simply by putting your finger on the muzzle perhaps?
-- coprocephalous, Nov 03 2008


// it would fire in air, underwater, even in a hard vacuum//
I'd've thought most firearms would, at least with limited exposure.
-- coprocephalous, Nov 03 2008


// underwater, even in a hard vacuum //

Underwater is a Bad Thing. But interestingly, in hard vacuum, conventional gas-expansion projectile weapons function perfectly well. The major problem is that of lubricants; many hydrocarbon lubricatns have unacceptably high vapour pressures, causing them to "flash off" even when the weapon is idle. However, there are silicone-based compounds that will allow the classic Browning .30-06 and .50 calibre equipments to operate in hard vacuum (and very low temperatures, such as those existing in LEO) without damage for useable lengths of time (several belts) without incurring excessive wear on the mechanism or the barrel. Bringing the weapon inboard for cleaning and relubrication does present technical issues, and the exotic allioys required to achieve the minimal differential expansion coefficents for both weapon and ammuntion (essential if jams are to be avoided) are not insuperable, and the technology may be regarded as "flight-proven".
-- 8th of 7, Nov 04 2008


bit of a bugger trying to sight one in in orbit.
-- FlyingToaster, Nov 04 2008



random, halfbakery