Trench art item

[PhilB]

If you look at a bullet that`s been fired, Aurel, you`ll see grooves along the side where the spiral rifling has bitten in. That`s because the barrel diameter is slightly less than the bullet diameter in order to get a good tight fit during its travel down the barrel. Here`s one from Hill 70 Loos. Phil B

[Aurel Sercu]

Phil,

Thanks.

I see. Life was hard for a bullet. (Sorry if it sounds a bit cynical.)

Just one more question. I knew about the spiral movement of the bullet in the barrel. I suppose that this spiral movement was (is) continued after the bullet has left the barrel ? Does that mean that a bullet sort of "drills" itself into ... its destination ?

Or does a fired bullet make tumbling movements ? I suppose not ? (A normal one I mean, not the ones the points of which were pinched off, or inserted in the cartridge the wrong way round.)

Aurel

[PhilB]

The rotation is not designed for the bullet to drill into things, but to help stabilize it in flight. I`m going to stop here because I know there are members who know a lot more than me about ballistics! Phil B

PS It`s an advantage of lead that it is soft enough to distort around the harder steel rifling of the barrel.

[museumtom]

The reason that the barrel is rifled is to keep the bullet stable in its trajectory, tumble is caused by the aluminium tip which is enclosed inside the cupronickel metal jacket. The bullet becomes unstable when it hits its target and the lightened tip makes it tumble and inflicts more damage to the receipient.

Thare ya go..

Tom

[Max Poilu]

Hi Aurel,

Sorry! I should have guessed that!

The calibre is the diameter of the barrel but not quite as simple as a measurement of the 'tube'. The calibre is taken from the bottom of one 'groove' to the surface of the opposite 'land', ie from a valley to the opposite hill.

The rifling can influence the behaviour of the bullet significantly. For instance a good old SMLE fires a .303 over a very long distance and causes it to spin a certain way and have a certain effect due to it's mass and velocity. However, the comparitively small US 5.56mm round as used in SLRs etc punches above it's weight. This is due to the fact that the spinning mostion imparted by and designed into the rifling of the SLRs firing these rounds is only sufficient to stablise the bullet over a shorter distance as it travels through the air. It is inherently more unstable than say, a .303 and will thus be more inclined to tumble and give up more energy on striking the target. I am not saying a 5.56 is more powerful than a .303 (it clearly is not) but basically a less stable 5.56 will give you more bang for your buck than a stable 5.56. And as always a lighter round = more ammo capacity, less weight and more control over the weapon.

[PhilB]

It is inherently more unstable than say, a .303 and will thus be more inclined to tumble and give up more energy on striking the target. .

The energy given up by a bullet (providing it doesn`t go straight through and out) will be its kinetic energy. This will be the same whether a particular bullet is tumbling or not. The tumbling bullet will clearly do more damage though. Is that about right?

What is the purpose of the aluminium in the nose?

I didn`t know that method of measuring calibre! Phil B

[Guest davidmac]

Could it be a tool for golf cleet cleaning?

Or a green marker?

[Aurel Sercu]

Giles,

Thanks for the clarification.

And ... surprising ... I understood !

David,

Golf cleat cleaner or green marker ?

I just don't know what to say. Except that I think that at the time and even for many decades later golf was totally unknown (unpractised) here. And I really don't know whether the item was ever meant for the UK.

Aurel

[Max Poilu]

The energy given up by a bullet (providing it doesn`t go straight through and out) will be its kinetic energy. This will be the same whether a particular bullet is tumbling or not. The tumbling bullet will clearly do more damage though. Is that about right?

Yes, but the 5.56 round as described above is inherently somewhat unstable and more inclined to tumble. There are many variables but a bullet with a high rate of spin is more inclined to go through soft tissue than a more unstable slower spinning bullet. If it is more unstable it is more likely to deform/fragment/tumble - all of which has a more devestating effect. If the bullet goes through the target it will only give up a portion of it's kinetic energy.

The US has always liked larger size rounds and Nato settled on the 7.62....but after all this the US later introduced the 5.56. It was based on a modified deer hunting round and led to the development of the Armalite rifles - first designed as a lightweight survival aircrew weapon - they of course gained far more widespread useage.

[PhilB]

The calibre is the diameter of the barrel but not quite as simple as a measurement of the 'tube'. The calibre is taken from the bottom of one 'groove' to the surface of the opposite 'land', ie from a valley to the opposite hill.

From "A Glossary of Firearms Technology":-

Caliber: (n.) This is a term with several related meanings which can cause some confusion. 1. The internal diameter of a gun's barrel. This can be measured either in English units or in metric. The measurement can be taken in a rifled arm either land to land or groove to groove. E.g., in most .30-caliber rifles, the diameter of the bore land to land is .300 inches, while groove to groove it is .308 inches. 2. Sometimes, caliber is used as a synonym for cartridge. E.g., "This is a .30-30 caliber rifle." 3. When used in reference to artillery pieces, caliber is used to measure the length of the barrel. A 5 inch/50 caliber piece would have a barrel 50 times the bore diameter, or 250 inches long.

So, do different people measure different ways? Phil B

[Max Poilu]

Hi Phil,

Oh!

Well, I guess only one method is correct - my information came from an Ian Hogg reference book. As you will probably agree, he has forgotten more about ordanance and weapons than any of us will ever know so I am confused. I am no expert merely an enthusiast and as always stand to be corrected.

However, there can only be one correct measurement - otherwise it would not go bang (technical term ) quite as designed.

[Max Poilu]

The measurement can be taken in a rifled arm either land to land or groove to groove.

Hmmm? But as you say Phil, this obviously gives two different results...the distance from groove to groove is obviously greater than land to land.

Confused.

[PhilB]

I`m sure there is a standard way of measuring calibre, G. It`s just a pity we don`t know it! Phil B

[Muerrisch]

And as always a lighter round = more ammo capacity, less weight and more control over the weapon.

Yes, and the inclination to blaze away at the least provocation. I wonder if hit rates per 1000 rounds have improved since '15 rounds a minute?'.

And the idea that a lighter weapon makes for more control is, shall we say, open to debate. Unless un-aimed fire at close range is the desiratum.

[Muerrisch]

It is inherently more unstable than say, a .303 and will thus be more inclined to tumble and give up more energy on striking the target. .

Surely a tumbling bullet has more KE, unless it starts to tumble after striking target.

[Max Poilu]

Sorry Aurel, your thread has been well and truly hijacked!

Surely a tumbling bullet has more KE, unless it starts to tumble after striking target.

The bullets kinetic energy is the sum (please see posts below) of it's mass and velocity. It makes no difference to this total if it is tumbling or not. Save, a very negligable amount due to increased wind resistance. In which case it will lose energy! As I say above: "If it is more unstable it is more likely to deform/fragment/tumble - all of which has a more devestating effect. If the bullet goes through the target it will only give up a portion of it's kinetic energy."

In addition a tumbling bullet in flight will not very likely go where it is aimed. The idea of the 5.56 is it has enough stability to go where it is pointed but no more than that - it is prone to tumbling on contact unlike a bullet that is more stable with a higher rate of spin.

Yes, and the inclination to blaze away at the least provocation. I wonder if hit rates per 1000 rounds have improved since '15 rounds a minute?'.

Yes, but the only men who were capable of '15 aimed rounds a minute' (or nearly 30 for many) were the highly trained first 100,000. Kitchner's army never learnt to shoot like that. For most soldiers in the Great War the grenade became the primary offensive weapon. The storm troop tactics of the 1918 German offensive led to the further development of the SMG which gained popularity through the 20th century. The SMG has now declined in use and the assault rifle has taken over as a more versatile and accurate weapon.

And the idea that a lighter weapon makes for more control is, shall we say, open to debate. Unless un-aimed fire at close range is the desiratum. [/i]

Of course not but I did not say a 'lighter weapon'! I said: "And as always a lighter round = more ammo capacity, less weight and more control over the weapon."

A lighter round produces less recoil and more control. In addition the rate of fire needs to be kept down to help control. 'Spray and pray' is not always the best policy...

[PhilB]

Sorry Aurel, your thread has been well and truly hijacked!

Surely a tumbling bullet has more KE, unless it starts to tumble after striking target.

The bullets kinetic energy is the sum of it's mass and velocity. It makes no difference to this total if it is tumbling or not.

Strictly speaking, its KE is half its mass times the square of its velocity. It could have extra rotational energy, but while in flight this could only be acquired (I would have thought) at the expense of its KE, since the rotation would be set up by the wind resistance (against the direction of travel) which would be bound to have a slowing effect.

(Which doesn`t help Aurel with his original query!) Phil B

[Aurel Sercu]

Sorry Aurel, your thread has been well and truly hijacked!

Giles,

It certainly has ! But the only one to blame is me, for it was me who gave the first push by creating the impression that I confounded the calibre and the length of a bullet !

But actually, I don't mind the hijacking at all ! I am watching, in utter amazement, the juggling with definitions of kinetic energy (either "the sum of the bullet's mass and velocity", or "half its mass times the square of its velocity"). And slightly enjoying them. (Physics was not really my favourite school subject, but compared to chemistry - absolute hell ! - it made me feel slightly euphoric.)

Besides, I have had a few replies regarding the trench art item itself (either the purely decorative destination, or a more functional approach), and I don't think that more will come or would have come with or without the hijack

Maybe I will erect a signpost in a different section of the Forum ("Equipment ?"), inviting the kinetic energy fans to join the club ! And then I will watch, but will certainly not join the Battle of the Giants !

Aurel

[Max Poilu]

Strictly speaking, its KE is half its mass times the square of its velocity

Phil, you are right of course, my fault for not making it clear but I did not mean sum as in addition but more the end result of a calculation involving the two factors....phew....I am off to watch the footy...

[PhilB]

Only reason I mentioned it, G, is because it shows that the the velocity is a more important factor than the mass as far as KE is concerned. Double the bullet`s mass and you double its KE. Double its velocity and you multiply its KE by 4. Phil B

[Muerrisch]

Rotational energy is a form of KE ...... try stopping a rotating bicyle wheel with your hand. I am not sure at trade-off between rotational and translational KE ..... Newton would suggest the total is conserved [other than frictional losses, negligible at range at which tumbling rounds are meant to be fired, ie very close.

[MikB]

Calibre measurement has so many conventions it's almost chaotic.

British imperial tradition was to use the bore (land) as distinct from groove diameter. The bullet needs to be groove diameter or nearly so, to prevent blow-by in the barrel reducing velocity, consistency and most importantly barrel life through 'gas-cutting' (which means exactly what it sounds like). Thus .303 uses a .311" diameter bullet, .577 a .590" bullet etc.

American military tradition was similar, but explicitly sized the bore in hundreds of an inch, so what Tommy called .300", GI Joe called 30 caliber. Again, the bullet was groove diameter at .308". Fritz followed the same pattern with 7,92mm, and I dunno what Jean-Paul did.

The spin imparted by rifling makes the bullet act like a tiny gyroscope - it tries to maintain the attitude at which it launched despite any forces acting on it laterally. This means that during the later part of a long trajectory the centreline of the bullet could be at quite an angle to the line of flight. In extreme examples, like battleship shells falling towards a target more than 10 miles away, they would be expected to pierce deck armour practically side-on. The spin due to rifling takes far longer to decay than forward velocity, because the only rotational friction is air-adhesion and the paddle-wheel effect of the burrs at the edge of the rifling impressions, whereas the forward motion of the projectile has to displace the air to allow its passage.

When the bullet passes through something more resistant than air, it is placed in severe compression because the nose has to do the work and is the area where the force of resistance is applied. This means the tail is effectively trying to overtake the nose. If you remember trying to turn over a gyroscope when playing with one, there is a strong tendency for it to 'snap' into the opposite attitude once you push it far enough over. A bullet, passing through tissue, will rarely encounter uniform and symmetrical resistance, and anyway it will already be skewed with respect to its line of passage if it has been on a long enough trajectory before impact. So the likelihood is that some imbalance of pressure will cause it to turn over inside the victim's body. The turnover force acting on the bullet can be very severe in denser materials - 303s recovered from sand-traps, for example, are typically bent into a vee shape, and sometimes even snapped in half.

This is where the aluminium tip on the 303s core comes in. The gyroscopic forces will try to centre the turnover on the longitudinal centre of gravity of the rotating projectile, ie. where the bullet would balance fore-and-aft if you put it on a suitable fulcrum. If that centre of gravity can be displaced backward, the nose, where the resistance forces are applied, will be further from that centre of gravity. Thus a glancing impact against bone, for example, will exert greater leverage on the bullet and be more likely to turn it over, sooner. If the bullet itself is bent in that process, it can no longer rotate smoothly about its axis, and the still-substantial rotational energy will be rapidly dissipated by chaotic and destructive movement through the tissues - 'tumbling'.

Dunno how nauseated you feel, but I've certainly had enough for now. Hope this has helped make a few things clearer.

Regards,

MikB

[Edward_N_Kelly]

And now to add to the fun.....

The comments on the 5.56 mm are a little inaccurate if wish to apply it to all the rounds of that calibre (and all the weapons that fire it).

Firstly "SLRs". Giles - in British Commonwealth service these are the 7.62mm x 51 NATO weapons derived from the FN-FAL. Variously known as L1A1, L1A2 and their Canadian equivalents C1A1 And C1A2.

Next - the 5.56mm came into vogue through the AR15 and XM16 family of weapons (I am aware that the AR15 was originally chambered for the 7.62 x 51 !) originally developed for the USAF in Vietnam. They fired the M193 5.56 mm x 45 (derived from the Remington .223 in Super Swift) in a 1 twist in 12 barrel. Combined it produced a round of less than spectacular stopping power, easily deflected by wind or foliage and just not a good round over all though it had the reputation of fearsome wounds in close ranges – this mainly from several rounds hitting in close proximity.

Being US - the troops went wild over it and it eventually became US forces wide armament.

This forced the hand of NATO who developed the SS109 round which required a new rifle twist (1 in 7) to get optimal performance so everyone went around and designed new weapons to take the new round. Ballistically it is almost better than the 7.62 mm x 51 in that it can penetrate the helmet M1 (the US "battle bowler" of WW2 fame) at 1,000m (the 7.62 mm pegs out beyond about 700m) due to its construction but it does not have the "carrying power" (or long rang) of the larger round (though there are few weapons or training regimes designed to use it that far out – the days of tripod mounted, indirect fire is disappearing fast).

Frank

[Max Poilu]

Hi Frank,

I think we are in agreement but I am not sure you really read my posts!

Firstly "SLRs". Giles - in British Commonwealth service these are the 7.62mm

Yes, I am aware that Nato standardized on a 7.62...! As I posted above: "The US has always liked larger size rounds and Nato settled on the 7.62....but after all this the US later introduced the 5.56. It was based on a modified deer hunting round and led to the development of the Armalite rifles"

Or AR15 as you say.

The comments on the 5.56 mm are a little inaccurate if wish to apply it to all the rounds of that calibre (and all the weapons that fire it).

I did not apply it to all weapons!: "However, the comparitively small US 5.56mm round as used in SLRs etc punches above it's weight. This is due to the fact that the spinning mostion imparted by and designed into the rifling of the SLRs..."

As I posted earlier my point was how the rifling can be designed to alter the behaviour of a bullet by the nature of the spin imparted. The 5.56 can be made to behave in different ways according to the weapon which fires it, obviously.

[PhilB]

Rotational energy is a form of KE ......

True, LB, but it could only be imparted by the wind resistance against the direction of travel - the negative direction so far as the bullet in flight is concerned. Which means it couldn`t add to the total KE in the positive direction, in converting to rotational energy? Only a following wind, faster than the bullet could do that! Phil B