6mm BBallistics:
Smoothbore VS Rifled VS Air Rifled

By Jymz on Thursday, June 25, 1998 - 02:10 pm:

As an ex paintball player <cringe> I'm used to seeing rifling on barrels. I've noticed the airsoft use smoothbore with a hopup. Seems to me that rifling would negate the need for a hopup. And then theres airrifling. Why wouldn't airsoft have any airrifled barrels? Seems to me it would take care of the hopup and the larger piston sizes needed. These barrels would create no suck and therefore a smaller , faster piston could be used. Anyways it all came to me in a dream. :) Feel free to flame me if you think I'm babbling

By Jacs on Thursday, June 25, 1998 - 08:51 pm:

actually u can get modification barrels for ur ASG/AEG with rifling...although most rifled barrel will have a bigger diameter than a smooth...good point on the hop up....: )

jacs,

By Chenshawn on Friday, June 26, 1998 - 12:30 am:

I think that adding rifling to a hop up gun is asking for trouble. The HopUp gives the pellet spin along an axis perpendicular to the direction of flight (horizontal spin axis). Rifling would try to spin the pellet along an axis parallel to the direction of flight. This nasty mix of angular momenta will result in a pellet tumbling is some unpredictable way.

The spin imparted by rifling acts, via gyroscopic forces, to stop a pellet or bullet from tumbling which would result in poor accuracy.
The HopUp spin along with the pellets velocity, acting through the Bernoulli effect, gives the pellet lift. This counters the force of gravity on the pellet giving it more range.
Different spins => different actions

By Almighty on Friday, June 26, 1998 - 01:30 am:

Rifled airsoft barrels were initially offered BEFORE the advent of hop-up. But because a BB is not always perfectly made (possible bubble inside) it may actually wobble, and eventually roll the spin forward, and make matters worse. Note also that rifled barrels have spaces (at the troughs) for air pressure to escape past the BB resulting in loss of propulsion power.

Rifled paintball barrels more often use the airrifling just so to distribute the "push" of air on the paintball. Paintgun barrel is so large that there is a tendency for the air to be directed unevenly.

The hop-up was actually more of a discovered effect after some guns shot differently when their barrles differed in alignment. Try this; on some gas guns (particularly old JAC m16s and some MP5s) let the barrel/muzzle droop down, and shoot - the BB will fly straight and true and far as if it had a hop-up.

By Flinn on Friday, June 26, 1998 - 05:49 am:

Rifled barrels would also bring troublesome legal implications to the sale of what are otherwise essentially toys with an age restriction on ownership [bit like motorbikes really:-))]

By Cthulhu on Friday, June 26, 1998 - 11:13 am:

Rifling requires that the rifled groves indent the projectile and impart spin. On a lead or brass projectile this is easy because barrel steel is much harder than the bullet metal. With airsoft bbs, the plastic is too resilient to be gripped by rifling. The rifling would allow air to pass by the bb and negate the hop up effect. The .68cal paintballs are too soft to be spun by rifling and contain a fluid center of varying density. Try spinning a raw egg. Wobbles? Now try to get it to spiral through the air like a football (american), then hit a man sized target.

The spherical shape is one of the worst ballistically (except for cubes and the like) for boring through the air. A round ball slows down very quickly in air and doesn't need a spin for stability. A long "bullet" shaped projectile is far supperior in ballistic performance, but it would require a complete redesign of most airsoft.

For the short ranges and low velocity's involved, the round bb in a smoothbore barrel is optimal. Many fine .177 caliber bb and pellet guns have smoothbore barrels. Many target and precision match air rifles have smooth brass barrels. My old Daisy 880 pellet rifle had its rifled steel barrel worn smooth by using bb's and it still gets .5" groups at 15m.

By Jymz on Friday, June 26, 1998 - 12:06 pm:

Yeesh apparently this topic has come up before. Well no matter what you guys say rifling is better than hop-up. If it wasnt my dads HK sniper system would have a hop up adjuster on it. Contrary to what you said about the hardness of materials comming into play, I would propose that this has no effective difference in this situation. The BB's no not have to "conform" to anything. The rifling , even if subtle, would still spin up the ball sufficiently to get it gyroscopicaly stable. On a real gun a bullet travels in excess of 1000fps and more. This energy deforms the bullet giving it it's tell tale grooves. However on a lower velocity system I still think that subtle rifling would be better than hopup. I do understand the bernuli effect. As a hangglider I know all to well about lift and its components. If you look at it though, whats worse? Having the ball hit a metal pin in the barrel to get it spinning , or having the ball follow sublte grooves to get it spinning. Seems to me same shit different pile. Maybe hopup is so popular because it can be adjusted.

On another note airrifling just the end of a airsoft barrel would prevent the dreaded suck at least. This would make a nice mod for some spring guns I think.

By Almighty on Friday, June 26, 1998 - 01:16 pm:

Some people don't get it. A plastic BB, given its size and weight, is easily affected by its own distribution of weight or density. If you go look at some split BBs, you may find that some of them have bubbles inside. This will affect the regularity of spin, and if it happens to be longitudinal (along the trajectory) close observation of the BB flight will reveal a corkscrew pattern. Over a long enough distance - forget using a rifled barrel because - you'd never hit the target, much less reach it. Rifled barrels produce low muzzle velocities.

There is no need to gyroscopically stabilize a sphere because from whatever angle you look at it - its still round. The coefficient of air resistance does not change. For a cylindrical object, tumbling effectively presents a bigger surface, ergo higher air resistance. That's why it has to be kept with the ends front-to-back. The best proven ballistic shape still is like a teardrop. And this has been adopted in one very controversial airsoft gun - the Asahi Firearms M40A1 Marine Sniper (Remington M700). It used what they called the "blade bullet", a pellet shaped like a blunted teardrop with a tail like the tip of a phillips screwdriver. The gun has been proven to shoot 100m. easily with very high accuracy.

Hop-ups are mostly for increasing the distance of "straight" flight. Instead of a ballistic curve, the flight is almost flat and level and then almost a sudden drop at the end. BBs tend to roll/spin as they travel through the barrel, so why not just deliberately set it into a desired direction and benefit from it? Oh yeah, hop-ups do not make use of anything metal to impart spin. The BBs simple encounter a rubber patch which forces them to roll over it in order to pass - initiating a spin. A bend along the barrel will do the same thing, and so would a slight difference in firing chamber-to-barrel alignment. Hop-up is popular because it really works, and cheap to produce - you can even make one yourself.

As for the "dreaded suck".. tha happens only if the VOLUME OF AIR pushing the painball or BB IS LESS THAN the INTERNAL VOLUME OF THE BARREL. This is prevalent in paintball because they have limitations on the length of the working pressure barrel yet need the extra length for better accuracy. If you don't port near the ends, the paintball starts sucking air from behind. Same thing happens to piston-fired airsoft guns. YO! Marui gun owners, take note. Barrel length is limited by diplacement - internal barrel volume MUST NOT exceed that of the piston/cylinder volume.

In many cases, widening or reaming the bore at the muzzle end of the barrel could help squeeze every last ounce of power. This is called "crater cutting". The underlying principle is that with the biggger bore at the end, air quickly overtakes the BB and slices a pathway against still air for the BB to pass thru. Simple but logical. There is a "wall" of undisturbed air which a BB hits after exiting the muzzle, and it immediately slows down the projectile. Break the wall and the BB rips through.

I'm no longer talking theories here...

By Jymz on Friday, June 26, 1998 - 02:52 pm:

A wall of undisturbed air hey, pfft yeah ok. What do you think happens to the air in front of the BB? does it get warped to another solar system? No it goes out the front "distrubing" the air in front of the barrel. In a perfect vacum what you say is true otherwise here on earth it aint. I understand what you trying to say but in my humble opinion guns dont get more accurate by people doing the same thing over and over again. People think up new ways of improving accuracy. This is called "evalution of design". I started this thread to propose some changes and maybe with all our tiny brains working together and your elaborate theories ;) we can get some crazy mods. Why not air relive the barrel half way down in order to use higher performance smaller pistons. And while doing that why not rifle the barrel. If your saying the only thing stopping people is the reduced air flow , why not just stick a bigger piston in. Geez I can see you have huge respect for hopup but i want my BB's to make it there with some punch, not arriving "birdlike".

On another note, do those blade style BB's have to be handloaded? of was that gun equipped with a clip to hold them. The same thing came on the scene of paintball 4 years ago. A clip fed gun with an ovalized paintball. Problem was they were the only manufacturer of this ball and of course they didnt get popular.Even though they could pressure load a clip and shoot much farther. Oh well. Seems we are all slaves to the ammunition manufacturers :)

These are just theories :P

By Chenshawn on Friday, June 26, 1998 - 10:02 pm:

I'm not sure if I agree with Almighty's "There is no need to gyroscopically stabilize a sphere because from whatever angle you look at it - its still round" theory. Forgive me oh Lord. I think that spinning a sphere longitudinally would stabilise its flight. With a big angular momentum component pointing straight along the direction of flight you would be less likely to have the pellet spinning randomly as it came out of the barrel, causing the pellet to shoot off in some random direction. The fact is that HopUp does exactly the same thing, just with a different spin axis and also you get the benefit of the aerodynamic lift on the pellet.
To increase the range it would possibly be simpler to use very small, dense pellets. I've been thinking about this possibility with my 4.5mm pistol. Getting dense, non-metal ammo is a problem though.
One of my team members suggested putting dimples on the pellets to break-up the laminar flow over the pellet (golf ball style) and reducing air resistance. It might work. Or not.

By Blackfox on Saturday, June 27, 1998 - 02:40 am:

I say I have to agree with Almighty. In Japan our team experimented with all types of riflings; cork screw, straight, Hop-up and so on (not air rifling though). Overall, Hop-up seemed to be the most effective. This was all done with air powered guns by the way. No electrics.

However, I would like to see how effective a cork screw air rifling would be on a long barrel electric. Perhaps a electric Hop-up gun with straight air rifling might be an effective combination too.

If anybody tries it, let me know the results.

Black Fox

P.S. Nice piece of work there Prof. Almighty. Well done.

By Cthulhu on Saturday, June 27, 1998 - 02:41 am:

I've heard of experiments with dimpled paintball, both conventional paintfilled and solid nylon versions. They were ballistically worse than normal paintballs in both range and accuracy. And it is economically impractical.

Despite what Jymz knowledge of hang glider aerodynamics tells us, the rifling grooves MUST indent the projectile to make it spin. Sorry to shatter any illusions, but bullets are larger in diameter than the barrel they're fired in. If it doesn't grip the projectile, the projectile will spin according to the distribution of weight and density. A "spitzer" (pointed) bullet will tumble end over end after a 50 yds or so. The angular momentum component is bunk if the projectile is completely unbalanced and out of round. According to him, only firearms generating velocity's of over 1000fps will enough energy to engrave rifling marks on the bullet. I guess all those forensic investigators are SOL if the murderer used a 230grn .45 ACP (830fps) bullet. Sorry, but I've examined bullets fired into water tanks and gelatin blocks for expansion. Even a .25 acp (MV~700fps) will exhibit rifling marks. Pellets from my pellet rifle have them too.
An round steel BB will not have measurably greater spin
or better accuracy with a rifled steel barrel. As I said previously, I have an air rifle with the rifled barrel worn mirror smooth from firing untold millions of BBs and it still shows excellent accuracy.
Also the projectile must be softer than the barrel material. There are no solid steel or titanium bullets because, in addition to being too light, they would ruin the rifling after a few rounds. Armor piercing rounds must be jacketed with a softer metal that can be grasped by the rifling.

By Almighty on Saturday, June 27, 1998 - 02:46 am:

Chenshawn..

Nomenclature error on my part.. but I had pressed the "post" already. Longitudinal should have been.. a lateral spin.

Anyway, good of you to point it out. Hop-up imparts a longitudinal backward spin and in doing so the uneveness of the turn is directed only along the up and down of the trajectory. An uneven lateral spin will cause the corkscrew.

Smaller and denser ammo will yield high penetration potential. Many people would balk at the idea...

Putting dimples should be easy enough. And it would work only in conjunction with a hop-up. We get sort of a similar action when we use some Taiwan made BBs that have rough finish

By Chenshawn on Saturday, June 27, 1998 - 09:20 am:

That's OK Almighty, sir, even the best of us make mistakes.

I would actually like to see some tests with dimpled pellets. From what Cthulhu (?!) says they might not be any good. Maybe somebody should get out there soldering iron and patiently melt lots of holes in a few pellets and then sand them smooth. Then test their ballistics. Yes, doesn't that sound like fun...not!

I was trying to figure out today, in between doing real work, what is the best combination of mass, velocity and pellet size. The problem with the ammunition we use now (0.2g is the heaviest affordable here) is that it is perhaps too light. A small wrinkle in clothing can dissipate the kinetic energy and the opposition doesn't feel the hit. But using a more powerful gun means more pain close up. Heavier ammo, slower velocities and more momentum and more hop-up may increase the effective "felt" range. However, putting the larger spin on a denser pellet would require a lot more energy. Hmmmmmmm, OK, I give up. Too many parameters!
OK, maybe someone could volunteer to be shot at varying ranges with varying pellet weights to see at what range he can feel the hits. Stalker perhaps?

By Eyegun on Saturday, June 27, 1998 - 11:59 am:

Why all this mental masturbation about squeezing another 5 or 10 feet out of your airsoft gun?? Face it: they shoot cheap, plastic, mass-produced BB's, and you can't expect a whole helluva lot outta that. Also, you probably shoot these cheap plastic mass produced BB's full auto, which will additionally degrade your accuracy and range. These guns are NOT precision insturments- they're just fun. The accuracy, realism, and fun (not to mention level of pain when you get hit) beat the shit out of paintball. If you want a precision rifle or something that will shoot 200 yards, buy a real gun.

By Jymz on Saturday, June 27, 1998 - 01:42 pm:

Despite what I know huh, I don't recall making any of these discussions into personal attacks. Do you have insecurity problems? Does this happen any time someones opinion differs from your own?

Rifling grooves do not have to indent the bullet. Thats right I said that. Induced spins can happen from even idle or subtle contact with a groove. Given enough grooves and a long enough barrel it will spin.you said "The angular momentum component is bunk if the projectile is completely unbalanced and out of round" ? Yeah that made alot of sense. You make alot of references to relative denisty of material. This isnt the 1800's , manufacturers can make uniform desity materials. Even a moron with a bowl and some epoxy could muster up a few good rounds. So lets quit talking about "mystery" air bubbles. Even paintballs dont change density for weeks now. Actualy about the only thing I can tell that changes density is you. You totaly took what I said out of context and it doen't even come close to the point I was trying to make. WHich is you dont have to force the bullet through a tight spot to make it spin. Don't make me get slow motion video of an old cannon to prove it to you.

This one takes the cake though "As I said previously, I have an air rifle with the rifled barrel worn mirror smooth from firing untold millions of BBs and it still shows excellent accuracy." classic. OK you probably don't notice any difference because it happened over as you state "millions of BBs" hahaha Well you see the human brain being used alone without instruments to tell it other variables makes for a weak point. I dont care how many times you seen yer wussy bb gun fired you can't tell the difference at 20 feet. The entire thing is too small for you to make an accurate judgement. Also your talk of taking bullets out of jello molds is lame. Do you think your the only self proclaimed expert on this? I don't own a single gun. Does this make me an amateur? Maybe, except for the fact both my parents are prison guards, ex FBI instructor, EX ERT SWAT leader etc. I had alot of this instilled in me when I was raised. So next time you think you should go and blow away someones opinion think again. You might be getting TAC training by me one day spunky.

The only thing I will agree with you on is your softer material comment. Did you think this all up by yourself? I couldnt imagine the huge equations involved with this one ;) Lemme see here all barrels I know of are very hard materials thats been tempered so it doesnt shatter as much as hard materials. This is very expensive, producing objets around $1000 or more for real guns. A bullet comes in under $10 even for a big one. Hey they must be cheaper to make huh ? Ergo they ant tempered or even using good materials. Like I said amazing grasp of these topics. No wonder so many people are in awe of your comments on here :) cept for me that is.

PS Im just in a bad mood, was supposed to go to Asia Pacific on monday and my car got fuckered. :)

By Mick on Saturday, June 27, 1998 - 03:17 pm:

To JYMZ
It is always great to hear about new ideas on how to make air soft guns perform better, but.....
In my experiens with real guns, airsoft and other tech stuff i have learned that teori sucks, testing, evaluation and sound technical knowhow is what it's all about.
in other words until an knowable educated expert shows some proof, i'm not going to change my hop up.
I'd rather play than talk.
oh and JYMZ you sound so angry???
lighten up man.

By Jymz on Saturday, June 27, 1998 - 04:06 pm:

Heh, yeah I'm a little pissed. I was really counting on going to Asia Pacific to learn some mods. Don't know if I can find a car fast enough to do it though. So you know frustration is released through writing ;) Sorry to contradict the norm here and all, maybe I'm just showing my ignorance :) but I digress. Anyone got a VW camper bus for sale? I'll trade you a 1978 Kawasaki 1000 Z1R heheh

By Cthulhu on Sunday, June 28, 1998 - 12:51 am:

To Jymz,
Sorry to hear about your car, but you need to lighten up. I don't think less of you as a human because you don't agree with what I say.
I was pointing out the irony in implying your background hang gliding taught you about rifling. I can just see the gliders spiraling through the air;) It was a joke.

I also corrected your remark that high velocity is required to impart rifling marks on projectiles. This is untrue. I'm not playing the expert, just stating fact. Just to clear things up, the bullets were fired into ordanance gelatin, not Jello. Jymz probably knows what this means, but I'll elaborate for those who don't. It is a substance that is used to simulate human tissue for ballistic testing, and is used by the military and cartridge companies. Water is not as accurate but is also used.

I worked for a specialty ammunition producer and I'm fairly familiar with real bullets and the effects of various types and rates of rifling (polyagonal, 12 groove, Microgroove, 4 groove, etc), but I'm no expert. I agree that even shallow slow rifling will induce a spin. So will a smooth barrel, but there is a minimum spin rate for stability, which varies with the weight and cross sectional density of the bullet. Shallow rifling won't work with bullets, lead round balls don't seem to need it.

I didn't post to impress people with my knowledge. I was trying to make the point that Airsoft bb's aren't bullets. Nor are paintballs. All too often people post tech info that is factually wrong, sometimes by just using the incorrect nomenclementure, and other readers who don't know anything about firearms take it as gospel. Then they use firearm and airsoft info interchangeably.

As Eyegun pointed out, BBs are massed produced and made as cheaply as possible. Even the TM's and other premium BBs have cracks, seams, air bubbles, and are far from round. Paintballs suffer the same fate, plus a liquid fill to add to the problems. Given the plastic BBs and low velocity's involved, it is my OPINION that cork screw rifling is not the way to increase accuracy.

To Jymz, or anyone who wishes to persue the rifling the airsoft barrels, you may want to read Understanding Ballistics and Hatcher's Notebook. Both have entire chapters on the ballistics of round balls, and the various types of rifling.

As for the "barrel suck" of paintball barrels, this site might have some info that can be applied to softs. www.paintcheck.com/articles/protips/range.html

Feel free to flame me if you think I'm babbling ;)

By Almighty on Sunday, June 28, 1998 - 08:28 am:

Cthulhu..

Thanks for the address of Paintcheck. It proves useful in proving my point about perforated barrels. The holes are there in order to keep the ball velocities within acceptable standards, and has nothing to do with range or ball stability.

I wish though that JLove had something on barrels that taper wider at the muzzle. This is something that paintball has not tried, but is now the norm in airsoft.

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