Tech question

[Fletchette]

Mods: I didn't know whether to put this in rifle, shotgun or another. Please move if you see fit.

Question: If the M1A1 Abrams tank with it's smooth-bore cannon can attain such a high muzzle velocity as well as great accuracy, why not a special shotgun round? Could a small flechette in a light weight sabot leave a smooth bore shotgun at significantly higher velocities (~4000fs) than a typical rifle?Could it be accurate? Why/why not?

[scott.cr]

4,000 FPS is really pushing the theoretical max velocity for smokeless powder. (The gasses themselves are barely breaking 4000 FPS.) Plus, if you were to launch something as heavy as a slug from a shoulder-mounted shotgun you'll be left in a world of hurt. Assuming a completely standard-weight shotgun and barrel length, etc.

Also bear in mind that shotgun slugs aren't as accurate as bullets because shotguns aren't generally considered precision weapons, and thus do not have accuracy enhancements as rifles do. You basically have a barrel that's not solidly fixed to the receiver whose harmonic changes as the weight of the mag tube changes. There are other factors, but those are two easy ones.

An accurate 4000 FPS shoulder-mounted smoothbore could probably be built... but it wouldn't be cheap!

[Fletchette]

I wasn't proposing launching a slug, but a light-weight flechette (well less than an ounce).

Also, the M1A1 cannon launches DU darts at ~5000fps, so there must be some sort of powder out there that burns this fast.

[scott.cr]

The projectile would need to meet a certain minimum mass to be able to carry this kind of velocity any meaningful distance. For this type of speed I imagine the projectile weight would be at least 500 grains.

I think the propellant for something like this would be closer to TNT than smokeless. The gasses would have to travel significantly faster than the projectile.

[Lee Lapin]

The individual-weapon flechette firing idea has been tried, back in the 1960s. See http://www.thegunzone.com/spiw.html and various other resources for data. The GunZone article mentions a smoothbore M-16 firing flechettes.

hth,

lpl/nc

[Rupestris]

Not exactly on topic but I'd love to see what kind of performance one could get with something like the Jada bullet in a shotgun.
It should make for a light, fast round.

http://www.jadaenterprise.com/images/bullet01.jpg

[Hawk]

This it?
http://weapons.travellercentral.com/ammo/shotgun_flechette.gif

See
http://www.antipersonnel.net/sdllc/002.html
http://weapons.travellercentral.com/ammo/shotgun_flechette.html
and (more background)
http://en.wikipedia.org/wiki/Flechette

The guy with what I take to be the pre-loaded rounds seems intent on loading a pile of 'em into a single round, thus getting only around 2000FPS out of a generic 20" Mossie.

I believe max theoretical of smokeless powders is around 6000, thus 4000 is about it for us mere mortals. I have no knowledge on the 5K military round but it seems plausible.

However, all the high numbers are out of rifles where 50,000 psi doesn't reduce the firearm to a single shot fragmentation grenade. Your typical shotgun, IMO, isn't going to stand for that sort of treatment on a regular basis (I could be wrong on this - I don't know what "normal" operating pressures are).

Using a sabot similar to that in the discontinued Remington product ( here (https://www.eabco.com/reload02.html) looks like a place to start), reducing to a 1.5mm dia flechette would likely reduce weight to where well over 4000 fps might be practical, given a smoothbore barrel (with rifle pressure levels).

Sounds like fun. Keep us posted.

[Waldo1]

Rupestris,

I think that it was PMC who used to produce cartridges loaded with that type of 'ring profile' projectile. Looked sort of like a heavily made cookie-cutter with a plastic plug in the base for a gas seal. I believe that these were primarily LE and self-defence pistol caliber loadings. I don't think that they are offered any more as factory loadings- liability concerns? Looks like a good idea that might have potential. Didn't US Army work on a 'ring-airfoil' grenade to be launched from auto/shoulder weapon that had flatter trajectory and extended range?

Stay safe,

[Jim Watson]

The roadblock to firing a saboted projectile at really high velocity from a SHOTGUN is the chamber pressure limitation, about 1/5 of what a rifle operates at.

As said, there has been a lot of work done with saboted fletchettes and subcaliber bullets in rifles. One paper study figured you could open a .458 Win mag out straight to use a .475" sabot holding a 100 grain 5mm bullet and firing it at 4500+ fps from a fast twist rifled barrel.

Fin stabilized fletchettes do not have a good accuracy record from smooth or slow twist (to separate the sabot by centrifugal force) barrels.

The novelty commercial fletchette shotgun shells are a joke. I shot some and there was no semblance of patterning or stabilization, about as many went through the target sideways as straight. I don't know if the military versions are as good as claimed.

Nothing new under the sun, the Hebler-Krnka saboted tubular bullet ca 1900 had high velocity for the day and long range by any standard, a 8mm supposedly carrying to 8000 yards. Penetration of 7 FEET in wood by the very streamlined steel projectile. Accuracy was poor but it might have made a good machine gun round for the long range doctrine of WW I.

[Fletchette]

The roadblock to firing a saboted projectile at really high velocity from a SHOTGUN is the chamber pressure limitation, about 1/5 of what a rifle operates at.

As said, there has been a lot of work done with saboted fletchettes and subcaliber bullets in rifles. One paper study figured you could open a .458 Win mag out straight to use a .475" sabot holding a 100 grain 5mm bullet and firing it at 4500+ fps from a fast twist rifled barrel.

Fin stabilized fletchettes do not have a good accuracy record from smooth or slow twist (to separate the sabot by centrifugal force) barrels.

Ok, the low chamber pressure makes sense. However, a gun could be designed around a higher chamber pressure.

The 4500+ fps is close to the Abrams' cannon; Does the Abrams use a special powcer to get the high velocity?

Does the DU spear have fins? I have seen slow-mo films of the sabot separating and it does not appear to have any rifling at all.

[Hawk]

DU = depleted uranium? I'm not sure if I'm looking at the right deal.

APFSDS (http://www.army-technology.com/contractors/ammunition/apfsds.htm)

but if so, the sabot is drag separated.

Guns that handle that type of pressure are common (rifles). The identity crisis that would afflict a smoothbore rifle is likely similar to what rifled shotguns routinely endure. :)

[Fletchette]

DU = depleted uranium? I'm not sure if I'm looking at the right deal.

APFSDS (http://www.army-technology.com/contractors/ammunition/apfsds.htm)

but if so, the sabot is drag separated.

Guns that handle that type of pressure are common (rifles). The identity crisis that would afflict a smoothbore rifle is likely similar to what rifled shotguns routinely endure. :)

Yup - depleted uranium.

Without rifling or fins, how is the dart stabilized? It is obviously very accurate.

[Hawk]

It has fins.

http://www.army-technology.com/contractors/ammunition/apfsds02.jpg

APFSDS = Armor Piercing Fin Stabilized Discarding Sabot

[mindpilot]

Perfect Illustration !!

[1911 guy]

Just over 4000 fps is the ceiling for smokeless velocity due to the gasses not breaking 5000 fps. Also, if I recall info from a friend (Jeff N.) correctly, the propellant in a tank artillery round is some sort of wonder junk closely resembling plastic explosive. In effect, a shaped charge directed toward the muzzle.

[Fletchette]

Thanks for the info, Hawk/1911guy.

The breech on the M1A1 cannon must be massive (or high-tech alloy, or both) if they use something like RDX as propellant.


on the subject of muzzle velocities and powder; the Paris Gun broke the 5000fps muzzle velocity without explosives like RDX. How did they do it?

[Jim Watson]

Don't take the 4000 fps (4400 and 4700 by some estimates) figure for powder gas expansion as gospel and an absolute maximum on bullet velocity. A firearm is not a laboratory calorimeter and is not operating at steady state. The Paris Gun got high velocity and long range the traditional way; a long barrel and a large powder charge, grossly inefficient, but nerve wracking to the French. (As what isn't?)

[KriegHund]

Would not a flechette round be extremely limited in its abilitys to inflict suffecient tissue damage?

[Hawk]

The round is listed as using 19 perf hex ja-2 propellant. Which, when fed to a search engine produces this:

Patent (http://www.freepatentsonline.com/6241833.html)

Claim 1 showing as:
A multi-based low sensitivity gun propellant having high impetus and ballistic potential comprising at least one matrix compound a major fraction of RDX particles combined with amounts of plasticizer components including nitroglycerin and amounts of methyl nitrato ethyl nitramine and ethyl nitrato ethyl nitramine.

I note that JA2 proper is not shown as containing RDX (in their spiffy little chart). The 19 perf hex persausion is, if I'm reading it right, 25% 5 micron RDX by weight, for which their simulation is showing a ME increase of under 2% (?!)
Ballistic simulations indicate that up to a 1.7 percent increase in muzzle velocity can be obtained using 19-perf hex granules based on bench scale batches of the material.

Overall it looked like pretty standard stuff until you mixed the RDX in, at which point, one achieved a slight performance increase. At this point I assumed I was missing something and quit reading. The stuff is over my head.

Y'all carry on, and let us know how it goes.
:)

'nother link (http://www.defense-update.com/products/digits/120he-mp.htm)

FWIW, I'm not at all comfortable with the "gas speed limits bullet velocity" saw because of a couple things I think I remember from my (mis-spent) childhood:

1. Deflagration values of propellants are typically sub-sonic. The characteristics of propellants are described differently than primary and secondary explosives. The general characteristics of propellants are: Burn rate-which is a function of pressure. Heat of combustion-calories per gram. Force-foot pounds per pound.

A standard type of smokeless powder has the following characteristics: Burn rate-.053 inches/sec at 1000 psi. Heat of combustion 1100 calories/gram. Force-375,000 foot pounds per pound.

2. In a rocket, maximum velocity may exceed exhaust velocity.

I can't back up either of the above points - I tossed 'em out 'cause, well, this is the shotgun forum, and they're more forgiving of my rambling here.
:evil:

[Fletchette]

Thanks Hawk.

I don't believe the maximum propellant velocity data either. I think it is a misrepresentation of the expansion velocity of an explosive when detonated in a sea-level atmosphere. You are correct about rockets - increase the pressure and the local speed of sound goes up. So there really is not a maximum velocity when confined in a tube (until you get into relativistic voodoo).

Another bit of trivia: releasing pressurized hydrogen (not burning, just pressurized) into a tube that contains a low pressure gas (a vacuum) will allow the hydrogen to accelerate to extremely high velocites - enough to cause small amounts of fusion at the end of the tube!

The velocity depends on the pressure difference (or more correctly, the pressure ratio), not the absolute pressure.

Yet more trivia: if the M1A1 cannon does indeed match the Paris Gun's muzzle velocity, than it should be able to fire it's depleted uranium dart into space (suborbital, not orbital, to perhaps 100 km)!

[dfaugh]

I, too, have been intrigued by something along these lines (shotgun fired sabot, fin stabilized projectile)...

Spent a bunch of time online reading all kinds of interesting stuff...

IIRC, the actual "upper limit" of gas expansion for conventional gun powder is more like 6000-6500 fps. Also, there are other factors that would influence pressure...In short, speed of the projectile wouldn't necessarily relate to higher pressure in the gun, so a shotgun MIGHT work OK, even though its not designed for high pressure...

There have been "cannon" built, that are capable of sending a small package into low Earth orbit. The Iraqis (I think) built a cannon into a hillside, that was expected to be capable of launching a projectile to Isreal (a L-O-N-G ways.) NASA has a "light gas gun" (hydrogen) that can shoot over 20,000 fps.

Sorry, I don't have links for all this stuff, but do some searches, and it makes for interesting reading, if not very practical

[Hawk]

I've got a number of little questioned items that I generally tend to stay clear of due to a lack of full knowledge on the topic (i.e. know enough to be dangerous) or the fact that discussion of some items is considered inherently irresponsible or just ticks some people off for reasons beyond my ken.

Shotgunners seem not to take themselves as seriously as some folks - it'd be my impression that a "myth debunking" thread here would ruffle less feathers than, say, on the rifle forum.

Let's start here: if a projectile's speed was bound by the upper limit of a propellant's deflagration rate rather than pressure differential, a pneumatic potato gun would achieve a maximum "spud muzzle velocity" of zero (no deflagration at all), right?

I'm sure gas velocity has a bearing on the issue but I don't know what it is. I'd bet it's not a one-to-one limit on projectile velocity, though.

Rockets aren't bullets but I was always fascinated that we could get a payload to 25,000mph using an H2 motor with an exhaust velocity on the southside of 10,000. (Actually 4.4KM/Sec). Not a firearm, but does illustrate a disconnect between "gas velocity" and "projectile velocity".

NASA (http://lifesci3.arc.nasa.gov/SpaceSettlement/Nowicki/SPBI101.HTM)
SpeedsOfSound (http://lifesci3.arc.nasa.gov/SpaceSettlement/Nowicki/SPBI1GP.HTM#speed of sound)

One item sure to stir up some at other forums is speed of a returning projectile fired straight up. After flirting with thread lock due to those thinking you're actually advocating the practice, you'll discover a breathtaking number of people that believe that it will return at precisely the speed it went up. (we're assuming normal atmosphere, here). Whereas shotgunners have generally, at one time or another, been "sprinkled" with #8 thus having an intuitive grasp of terminal velocity. ;)

Next up: "pressure curves" smokeless vs "black" powder...
:evil:

[richardschennberg]

There is a science called "interior ballistics." One of the unique phenomenons is that the velocity of gasses (and hence, the projectile) inside the barrel can be considerably higher than the exhaust velocity of those same gasses after they leave the barrel. Usually, however, the gasses briefly outpace the projectile, which is why you have to chronograph at least 6-10 feet out ahead of the muzzle (and then be careful not to shoot the device!).
Richard
Schennberg.com (http://www.schennberg.com)

[Hawk]

A little factoid from the .50BMG folks that bothered me to no end as it seemed counter-intuitive: a muzzle brake derives none (or close to none) of its effectiveness from directing the gases rearward. A brake such as the Vais (http://www.muzzlebrakes.com/) is as effective as the sharkgill type brakes commonly seen. The rearward vectoring is just a styling lick.

The FCSA addressed only recoil reduction, not muzzle flip. However, I tend to wonder if the holes drilled in the top quarters only of competition shotgun barrels would work every bit as good if drilled around the full circumference, or for that matter, on the bottom only. Are they drilled as they are for no better reason than that's what we expect to see?

A Google search on "shotgun barrel porting" turns up a pantload of hits. A search on "shotgun barrel porting tests" is conspicuously sparse. In fact, the number one hit (and only apparent independent one) is a rather self-effacing page stating "no discernable difference". There's enough contervailing stuff to keep the debate alive, albeit mostly sponsored by those selling the service.

Muzzle brake effectiveness is proportional to muzzle blast and might be expected to provide some benefit in light guns shooting heavy loads. However, they're turning up on heavy-ish sporting clay guns shooting light-ish target loads.

Maybe the next Brister will bolt an 8 pound ported O/U shooting AA target loads to FCSA's apparatus (or similar) and do a paper on "Porting and the Placebo effect"?

Or not?

[Fletchette]

I don't think porting on the top of barrels (shotguns, rifles or pistols) does much at all. On pistols, the recoil may just go down due to a reduction in muzzle velocity.

In ordre for the light gasses to generate much thrust, they would have to be accelerated to supersonic velocities (as happens in a rocket nozzle) and directed rearward (not good for handguns!). Effective recoil reduction using this method leads to the "recoiless rifle" designs of the fifties - basically bazookas with extremely short burning rockets!

[Hawk]

So...

I dig out the FCSA stuff and read it nice and sloooooow, to see if I can figure out why rearward vectoring on a muzzle brake makes not a whit of difference.

By George, I believe I've got it:

When fired, there's a good deal of ejecta, besides the bullet, heading down the barrel with a fair amount of forward momentum of its own. (context here is a .50BMG).

The muzzle brake "bleeds off" a portion of the ejecta, thus taking on some of the ejecta's forward momentum - this is what provides the "forward thrust" on the rifle - nothing to do at all with venting the gases rearward. (this was the "ahh HA" moment). Thus the Vais performs admirably on the .50 even though it has some vents facing forward.

Sir Isaac would be proud - no voodoo, just simple transfer of momentum from ejecta to brake.


Muzzle brakes vs Porting.

A muzzle brake's efficiency is partially determined by the internal chambers and how well "ejecta" is drawn off with concurrent transfer of momentum.

My conjecture is that porting on a relatively thick-barreled handgun is actually functioning as a type of brake. Again, the portion attributable to venting direction likely has not been isolated in the limited tests of "porting" although I'd concede that it likely exists to some extent. Also, a "real" muzzle brake will be seen to handily outperform "porting".

Given the thin-walled nature of a shotgun barrel, the reduction in recoil attributable to "muzzle brake" effect is likely negligible, leaving our "thrust vectoring porting" to do all the work. Since a "real" muzzle brake gains approximately zero effectiveness from its "porting", I'm betting porting of shotgun barrels has just over zero impact on recoil, muzzle lift or the life cycle of the Mayfly. It has a fair impact in making the arm more "interesting" to clean.

Oddly enough, one of those old-timey Cutts probably actually worked - at least as well as can be expected given the "ejecta" associated with a 12Ga is probably a good deal less to work with than that provided by a .50BMG.

OTOH, porting certainly doesn't hurt, so if I were to get a Browning sporting, I would not feel compelled to fill the holes in. They're simply useless.

Comments?

[richardschennberg]

A little factoid from the .50BMG folks that bothered me to no end as it seemed counter-intuitive: a muzzle brake derives none (or close to none) of its effectiveness from directing the gases rearward.
Yes, but the pressurized gasses pushing forward on the muzzle brake (and not back, where the gasses are directed) create the net forward force. So even though the gasses excaping to the rear are not directly causing the forward push against the recoil, it is in the same direction. The same thing happens in a ported shotgun barrel. The actual downward force against muzzle rize is caused by high pressure throughout the bottom of the barrel while there is very reduced pressure at each hole in the top of the barrel. Gasses do escape out the top. The ports work because there is more force pushing the front of the barrel down than up.
Richard
Schennberg.com (http://www.schennberg.com)

[Hawk]

But do the ports really work?

This technoid (http://www.shotgunreport.com/TechTech/TechnicalTracts/ChokePort.html) link came up in a search for "shotgun barrel porting tests". Admittedly, not looking real updated and certainly doesn't take itself too seriously.

Ya gotta love quotes like:
Technoid conducted a blind comparison (some say that
all of the Technoid's comparisons are blind)

Anyhow, I didn't find anything stating that porting did work (apart from maybe heavy loads in an unrestrained gun) that wasn't directly associated with a porting vendor. I believe I understand the concept of the ports, it's just that I'm not certain there's sufficient pressure to actually do anything.

Has anybody strapped something like a Browning Gold sporting in an FCSA or Ransom type contraption and tested with ports "as supplied" then blocked off?

I'm not saying ports on a sporting clays gun don't do anything as I don't know that for a fact, however, I find the concept that their real world use is along the lines of SM's "bells and feathers" (psych out the competition) strangely compelling.

...and there seems to be a real lack of tests for a procedure that's likely to be found on several hundreds of thousands of guns and is being actively promoted by a slew of vendors. I tried duct-taping the ports in a buddys O/U and noticed no difference. However, that's what I was expecting to find and thus those results are admittedly meaningless. Anybody got any personal "before and after" impressions?

[106rr]

Steyr developed a "needle gun" type of anti rank rifle. It had no buyers because while it could penetrate much armor it didn't cause much damage inside the vehicle. It was a high velocity round with a rifled bore.
The smoothbore cannon barrel has more than one purpose. Traditionally anti tank weapons (like the 106 Recoilless Rifle) fired shaped charge loads. These were designated HEAT - High Explosive Anti Tank. There were other types of anti tank loads such as the HEP-T. This was a High Explosive Plastic- Tracer. It was a spalling round, that is it created an explosion on the surface of the armor which sheared off metal plating on the inside of the vehicle. The HEP-T is not a shaped charge. The Flechette rounds were called "Beehives" for their peculiar sound in flight. They contained a little over 10,000 flechettes with a timed fuse on the tip of the projo marked for distance from M/A to 3500 meters. M/A stands for muzzle action. The small bursting charge would break the jacket allowing the centripital force to spread the cone shaped layers of flechettes out to a 100 meter pattern at 100 meters from the designated setting. These were most commonly used at the M/A setting at point blank elevation. The timed fuse often malfunctioned. I fired at least one directly into the side of a mountain when the fuse failed.
The shaped charge must have a starting velocity of less than 1600 fps in a rifled tube to be effective. The rotational speed upsets the shaped charge. Thus low velocity limits the trajectory in a rifled tube. The smooth bore can achive a higher velocity without upsetting the shaped charge. The sabot loads can achieve a higher velocity than a shaped charge. A smooth bore cannon has greater versatility and service life than a rifled bore.