bullet accuracy?

[FUTI]

Reading a thread about making barrels I got nice idea but since it was very much of topic I choose to start new thread. I don't know much about this area so it is maybe irrelevant, but anyway...

Here it is...I remember that there was a solution that make tank cannons projectile more accurate. It consisted on the fact that projectile leaving the bored barrel will have momentum, and that was corrected by using a small plastic wing end that used wings to give the projecile the momentum in the opposite direction in the second half of the trajectory. Given the diferences in size that can influence aerodynamics of the projectiles is something similar possible/necessary with rifle bullets?

[tomu]

Are you talking about saboted rounds, usually Kinetic Energy projectiles which have have fins?

The only thing which comes to my mind are flechettes which are used mostly in shot gun ammo. There are some rare, more or less collector pieces, modified Mod. 1911 A1 pistols the OSS/CIA fouled around with which shoot arrows stabilized by fins.

[FUTI]

Yes I thought about that. Is there any benefit with that approach? I just can't make my mind on that subject. It should be some benefit in accuracy, but I assume that also there is going to be reduction of velocity so maybe kinetic energy can be smaller. In tank projectile that doesn;t matter since its payload is HE charge, but rifle ammo... Is there any study of that kind known to you? Accuracy or kinetic energy...what is valued most in rifle use?

[SweNMFan]

Swedish army snipers have a sub caliber 7.62x51mm round that is used in the the swedish version of the Accuracy International L96A1 AW.. It is a 4,81mm tungsten sabot with a V0 of 1340mps instead of the regular 785mps.. It is Winchester developed and made..

Usally its named 7.62 SLAP, (Saboted light armour piercing) or M948 in US inventory and there is .50cal SLAP rounds as well..

In tank projectile that doesn;t matter since its payload is HE charge

The tank sabot rounds do not have any explosives in them. They are kinetic penetrators.

A HE or HEAT round have parts attached ot them to make them spin even in a smoothbore barrel .


Accuracy or kinetic energy...what is valued most in rifle use?

For a sniper accuracy, not much point in having massive kinetic enery and not being able to hit a barn with it.. :p

[Jacks Complete]

And for a tank-killer, massive kinetic energy, since the target is quite big.

Range would be quite important there, too. Every step closer to the enemy you have to go, the more likely you are to be in range for him!

[FUTI]

I agree SweNMFan, but as you see from posts other made here, I have some doubts. Air rifle where used in old days as sniper weapon of choice due to precision.

But there is now two problems more. First target can have bullet-proof vest reducing the posibility of efficient hit which can cause at least reduction in your targeting to few unshielded spots (solution A) or you need bullet with higher energy to penetrate the vest (solution B). Second problem is that range of weapon is higher if it has more kinetic energy related to bullet initial velocity at gun mouth - I hope this is the term used.

So if the technical mean used to improve bullet accuracy reduce its range meaning that enemy sniper has not-so-small advantage, I would feel uncomfortable using it, and if it also reduce its penetration/hit ability I would abandon the use of it. And I'm afraid that is exactly the case with the solution I describe at the begining. I wish someone can improve my observation on this and prove the opposite.

So far this thread show that noone here didn't stumbled over some study made in this subject...but I have hope:)

[Jacks Complete]

FUTI,
a high-powered air rifle, with a silencer, would be superb, since there is no muzzle flash, no smoke, no IR trace, not even a loud cough noise! The only thing that could determine where you were would be a radar based system, or, after the fact, putting a rod in the hole.

You could, perhaps, defeat the radar system by use of a radar absorbant coating, since it wouldn't burn off with the shot.

You could get very close. 50 yards, perhaps, and ensure you get the kill. You would be well within range of anything the target had then, though.

I would want the usual combo, which is great accuracy, followed by lots of power. Accuracy *always* comes first, though. A .22 to the head is far more likely to kill than a .50 to the hand. A .50 to the head, however...

One way to increase accuracy, at the expense of a little range, is to not put every last drop of power into the rifle cartridge. Backing off a little often helps increase the accuracy by a long way, and you are only losing a few hundred feet per second on a rifle round.

[Microtek]

SweNMfan: Actually, even modest rotation drastically reduces the effectiveness of HEAT rounds. I think there was a system working the other way, that is a freely sliding sabot so you could fire a fin-stabilized system from a rifled barrel.

Regarding the use of aerodynamic stabilisation of small arms projectiles, there is the problem that the effects of fins don't scale, so you need a certain minimum caliber for it to be effective. I don't know what caliber that would be though ( I'm guessing something like .50 cal ).
There was however, a patent about a tranquilizer system which fired very thin projectiles ( 1 mm diameter, 15 mm long and with the center of gravity lying less than 30 % of the projectile length from the tip ) from a smoothbore weapon.
They conjectured that it would be possible to scale the gun up as long as the projectile dimensions were scaled as well.

[FUTI]

Microtek you maybe corrected me with last statement. If I understand your post right then mine previous assumption that counter-rotation of sabot in downward/second part of trajectory (caused by fins made in such way to use air flow to create resisting angular momentum - something like curved ball - felsh or something- I will start to learn ordinary English terms, chemical language is of little help here) is used to correct the error caused by fireing sabot from rifled barrel is completely wrong. I thank you for this, I never look at this matter the way you did:). I only modestly ask you can you back that with some paper, link, document or something because both of us are burning our brain cells to extract some long forgoten back-ups of data from time when there was no W&E Forum for brainstorming activity.

[Jacks Complete]

I know it is true about rapid rotation killing jet formation in shaped charges.

You are trying to throw it together, but the rotation is trying to throw it outwards. It will amplify any mass errors.

A slow rotation, say a few hertz or less, I'm not so sure about. I've seen slow-mo footage of shaped charge warheads spinning into the target at slow rates, about half a turn per length travelled.

Remember, stability by rotation for a bullet requires spin rates that would be insane anywhere else.

[prespec]

The tank guns you refer to are smoothbore, so require fin stalbilisation to avoid projectile yaw, and most are wire-guided .

Rifle bullets are stabilised by the rifling, and require a certain RPM to stay that way , which is in direct proportion to their length.

A longer bullet of a given diameter will require a faster twist-rate to stabilise it, but is more efficient , due to it's greater sectional density.

The RPM is governed by the rifling twist and the muzzle velocity.

Other factors contribute to its ability to maintain velocity, including ogive and tail design.

When a bullet passes back down through the sound barrier , it can lose stability also......that is why boat-tail bullets work well past the 600-800 yd mark in normal military/hunting calibres. The boat-tail reduces drag and is more important in the lower speed ranges.

The idea of fins on rifle bullets would seem to be in conflict with these requirements, especially the need to maintain rotation at longer ranges.

[Jacks Complete]

No, the tank guns aren't all fin stabilised, not always. The UK Challenger tank guns are 120mm rifled barrels. TOW type missiles are wire guided, but they aren't 'bullets' from a gun, they are a neat way to use the gun as a missile launcher.

Firing a saboted round designed to stop spin is a good idea, otherwise the bullets fins would be ripped off or flattened instantly it hit the air outside the barrel. Something like 1% of a bullet's energy is stored in the spin. The reduced drag of the sabotted projectile would be made up for slightly by the increased drag of the fins on said projectile.

[amachinist]

I know this thread is geared more toward cannon barrels, rifle and pistol barrel accuracy is also affected by the quality of the crown and the last couple of inches of rifling near the muzzle.

[prespec]

I know this thread is geared more toward cannon barrels, rifle and pistol barrel accuracy is also affected by the quality of the crown and the last couple of inches of rifling near the muzzle.


Nicely stated. It is the most critical area in an un-guided projectiles journey.

Far more influential than the throat, as it is the last point of contact with the weapon, so any inconsistancy here will allow propellant gasses, travelling at several thousand FPS faster, to impart 'tip' or yaw to the projectiles path.

Look after your crown.