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OK, for the younger viewers amongst us :wink:


Could someone please explain calibre when it comes to weapons. For instance, the US M1 carbine is .30?! Yes, no? So too is the Garand and the .30 cal machine gun? Yes?!


The Enfield is a 303 and the Nato round is 5.56 but I have heard that some UK forces may be going back to 7.76.


Then we have the . 50 cal and the 88mm.


So what the hell are all these measurements about, what part of the set up is 88mm for example?






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Caliber is the diameter of the inside of the barrel. It is effectively the size of the projectile diameter. In a rifled barrel the distance is measured between the lands. In the English system this is measured in Inches or parts there of. In the metric system it is measured in mm's.


Caliber is a term also used to measure the length of a barrel (from breech to muzzle). The length of the barrel affects the internal ballistics performance. Once the shell or bullet has left the controlling influence of the barrel, external ballistics take over, and the shape and spin rate etc affect performance.


The given caliber does not indicate the length of shell case or charge housed within it. A short case or a long cased shell or bullet, could still be clasified by the same caliber rating.

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For calibre, you have to go back a bit into history and remember that precise measurement was a bit difficult until quite recent years.

Initially, guns were very weak and could only fire lighweight stone shot. The gunners chipped their own and basically carried on chipping until it 'fitted' which really just meant it fell in. The idea making all shot or all guns the same did not exist.

Once they tried to make guns the same size (eg on a ship) they needed a way of measuring the bore and it was easier to weigh a shot that just fitted, hence why the HMS Victory is armed with 9, 18, 24, 32 and 68 pounder cannon. In each case this was the weight of an iron sphere that just fell into the bore. The same idea was used for most shotguns and pistols but in this case it was the number of round fitting lead balls that weighed a pound so a 4 bore shotgun fitted a round ball that was 4 to the pound, a 12 bore had a ball that took twelve to weigh a pound etc.

Even if firing small shot like shotguns, all of these guns were sized to a ball and all were fired direct at a target. In the 18c they started to fire what we would call bullet shaped, hollow 'shells', usually filled with explosive. Because these were long for their diameter and also hollow, the weight of them could not be used for measuring the hole up the middle of the gun so they went to measurement in either inches or millimetres. It usually was an exact measurement of the hole, not taking account of the grooves that would commonly be put into the bore to spin the shot, called rifling but some makers measured groove to groove which would seem a bit bigger than just measuring the hole.

You could still see the ghost of this system until quite recently with the 2, 6 and 17 pdr anti tank guns (direct firing, measured by the old system, even though they do not in fact fire a round ball) and the 3inch, 5.5 inch and 75mm which had all started as shell firing, indirect weapons.

Nowadays, it is pretty universal to use mm to measure the bore so the Braveheart fires indirect and measures 155mm bore, Challenger fires direct but is still measured in mm, 120 in that case.

Sometimes a maker will 'lie' about the bore, so that it sounds better: .303 is actually .312 of an inch, most .38 pistols are actually .357 inch bore and the Comets 77mm gun is actually 76.2.

Note that the hole up the middle is not the only measure of gun power. A shot can be longer and heavier than another of the same diameter and a bigger case of propellant ('gunpowder') can throw one shell a lot quicker than one in front of a small case of powder.

You mention 88mm, this was a heavy shell (18 pdrs or so?) fired with an enormous charge of powder as a tank or anti aircraft gun. The brass case is probably 3 feet long and the shell comes out of the gun at maybe 3800 feet per second. The 25 pdr is very nearly the same diameter (bit smaller actually) but longer and heavier. It has a much smaller powder charge, in front of a case about a foot long. The 25 pdr shot struggles to top 1500 feet per second.

All of this is from memory: if anyone can correct the figures above, please do.

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In a rifled barrel the distance is measured between the lands.


In an English barrel the calibre (sp!) is measured land to land; in the US, it is measured valley to valley, hence US 76.2mm equates to UK 76mm. I'd posit that in small arms, the difference is negligible enough not to make a difference.


Referring to a weapon as a 30 cal or 50 cal is an Americanism. The usual British reference to these particular weapons is Three-Oh or Five-Oh (Browning). It means .50".


303 = .303" (watch out for American "3030"s pronounced Thirty-Thirties = .303")

22 = .22"

.223" = 5.56mm (Nato Standard)

7.62 = 7.62mm


With tank (German: Kampfwagenkanone) and anti-tank guns (German: Panzerabwehrkanone), don't get a UK nomenclature (e.g Ordnance, Gun, 76mm L23A1 on Scorpion) confused with the "length in calibres" (e.g. 75mm KwK 42 L70 on Panther).


L23A1 describes a UK model number. IIRC the GPMG on Scorpion is an L43; on Scimitar an L37, yet they differ only cosmetically.


L70 indicates that the length of the barrel is 70 times the calibre.


Put simply, from pulling the trigger, the explosion of the cordite in the case causes the round to accelerate down the barrel until it passes out of the muzzle. At this point, the gases escape, acceleration stops and thereafter the raound slows due to friction with the air. In particularly long barrels, timing the opening of the breech after the round has left the barrel is a black art: open the breech before the round has left and the backblast will kill the turret crew, so you'll see a bore evacuator part-way down the barrel. Like in a gas-operated rifle, this starts to bleed off the gas before the breech seal is opened and helps ensure that the gases are expelled forward out of the tank, not backward into the turret. Scorpion was found, upon firing, to flood the turret with carbon monoxide every time a round was fired and this is why it was taken out of service. I can vouch for the number of times I suffered carbon monoxide poisoning while firing Scorpion.


Hence muzzle velocity is the maximum speed of the round. The longer the barrel, the greater the muzzle velocity and the more kinetic energy available to a kinetic tank-defeating round (AP-T, APC-T, APCBC-T, APDS-T, APFSDS-T, etc). Less important in rounds containing HE (HE-T, HESH-T, HEAT-T, etc).


Compare the main armament on a Tiger 1E and Tiger II: IIRC, L56 vs L71. Thus the Tiger II's gun fired a vastly more powerful AT round than that of the infamous Tiger 1E even though AFAIK they fired the same rounds. In fact, ISTR that, comparing ballistics charts for Panther and Tiger 1E, at longer ranges (approaching 200m IIRC) the Panther's 75mm had better armour-defeating characteristics that the Tiger's 88mm.


("-T" indicates a phosphorus trace in the warhead to track the round in flight. The only tank round I have ever been aware of that didn't have a trace was smoke: so long as it wasn't over-fuzed and buried itself in the mud before going off, you couldn't really miss a smoke round, which was so slow in flight that you could follow it with the naked eye anyway. All other rounds tend therefore simply to be referred to without the "-T" suffix.


Note that there are Geneva conventions governing the use of trace in small arms rounds. Used against infantry, rounds may be loaded as four ball, one trace, so that in a burst of ten rounds, two will give you an indication of where the burst went. As a coaxial rangefinder, one ball, one trace is permitted.


In Northern Ireland a friend carried a 7.62" LMG ("Bren") and IIRC 160 rounds of 7.62" in eight mags of 20. They were supposed to be four ball, one trace, but he worked on the principle that by loading all the trace into the first two mags, he could hosepipe his target and be sure of getting the kill, then bring down another six mags of ball into the body and risk somebody actually working out what order he'd fired the bullets.)

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An addendum to John Pearson's post which you may (or may not) find interesting.


At the end of the 19th Century, every country started to look seriously at field artillery. Design of a field gun did not involve choosing a calibre and building a round to fit: quite the reverse. Decide what you want the gun to do (how far will it fire, how much explosive will it deliver onto the target, how high the round must fly (think howitzer), etc). Then design a round to deliver that payload and a gun to deliver the round.


Curiously, everybody had a similar idea about payload and IIRC between about 1895 and 1905, most countries produced a 105mm field gun (notwithstanding how they described the gun, e.g by wieght of the round or calibre in inches, etc). The notable exception was the Swiss Army (whose main weapon now appears to be a knife ;o) which developed a 104mm gun.


In the same way, many countries produced pistols firing 9mm rounds (even though the actual bullets were different) and there were so many rifles etc produced at around .30", .303", 7.62mm, 7.92mm, etc.


By the end of WW2, the British recognised that the .303" round was far too powerful for the modern battlefield, so the Royal Armaments Factory at Enfield developed the EM1, then the EM2 firing a round of something like 4.85mm. The guns were revolutionary in having the working parts behind the trigger occupying the space that traditionally comprised the stock.


Unfortunately an American war machine that had produced untold millions of rounds of 7.62mm ammunition was adamant that the newly-formed NATO would standardise its rifles around this round. With all that development work wasted, the UK took the Belgian FN 7.62mm rifle effectively straight from the shelf (with minor mods ... oh and of course in our Army we only fire "single aimed shots", so there is no need for an automatic capability) and called it the SLR.


The Americans promptly fired their way through this bullet mountain in Korea, and when they went to Vietnam, they realised that the 7.62mm bullet was far too powerful for the modern battlefield, so they built a 5.56mm version of their M15 assault rifle and called it the M16.


With a view to a total overhaul of all Army systems from boots to field guns into the 1980s, the EM2's plans were dusted off and used as a start point for the SA80.

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AFAIK - the ony 7.62mm rounds in use within NATO these days are for the GPMG and whatever the snipers weapon is these days (in mine it was the SMLE Mk IVT). AS ever - fully open to correction on this as I've been out of touch nigh on 30 years.


Again - AFAIK - we went to the 5.56mm round in part due to political lobbying over the fact that in an urban environment the 7.62mm round is so powerful it will go through the wall of a house and still have enough power left to kill whoever is the other side of the wall. The facts that some of the time the wall penetration was intentional because IRA/UDLA whatever lowlifes where sheltering there and that the groups doing the most lobbying were the political arms of these factions are of course purely coincidental.

I guess, though, that reducing the risk of injury to non-combatants is a valid reason.

That said - having seen what a 7.62mm round will do and what a 5.56mm round will do at the 200 to 300 metre ranges my personal preference will always be for the 7.62mm as I'm a firm believer in the philosophy of the art of war being to make sure the other person dies for his country instead of me for mine!!


oh and of course in our Army we only fire "single aimed shots", so there is no need for an automatic capability) and called it the SLR.


Never come across the VERY unauthorised modification to the safety mechanism that converted the L1A1 to fully automatic as per the original FN????

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I'm a firm believer in the philosophy of the art of war being to make sure the other person dies for his country instead of me for mine!!


oh and of course in our Army we only fire "single aimed shots", so there is no need for an automatic capability) and called it the SLR.


Never come across the VERY unauthorised modification to the safety mechanism that converted the L1A1 to fully automatic as per the original FN????


The latter day thinking is that it is better to seriously wound the other guy rather than kill him. Kill him and his side are down one man; wound him and they are down 12 people while they casevac him, patch him up and help him recuperate.


As for the SLR. I have to confess that this beautiful weapon was only my own for a short period in Northern Ireland and another short period when I first transferred from cavalry to pay services. During my time in the RMP, my personal weapon was the Small Metal Gun and alternative was 9mm pistol; in the cavalry, SMG then SLR.


I did frequently fire the SLR competitively - by coincidence, I am unusually working from my front room and I can see my trophy cabinet from here. But not surprisingly, automatic fire from an SLR was not one of the competitions.


It served me well when a colleague fell off the Matterhorn and killed himself. I returned from leave and was told to dress for saute-the-coffin training and be SLR-drilled for a week by a Green Howards drill-pig. I was able to bluff the REMEs that surrounded me but when the drill-pig marched on from the other end of the drill square 1/4 mile away and screamed a word of command, he could tell and started screaming. So I looked him in the eye and pointed out that I had NEVER done rifle drill in 9 years. This was inconceivable to an infantryman and I did so enjoy watching the veins pop in his neck.


He kicked me off the square. I muttered, "I told you so," and bimbled off and got on with some real work.


A few years later, the Adjutant General was to open his new Computer Centre and Sgt Alien was shortlisted to be a part of his Honour Guard. Needless to say, I tried the same trick, but sadly the RSM was not stupid and I and another transferred-in ex-RAC got a crash course in rifle drill.


So yes, I am aware of the SLR sear mod, but never had cause.



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Ah yes - rifle drill - did it in 215 Sqdn RCT - inc the (by me) dreaded "pokey drill" wherein one was required to hold the SLR by the flash eliminator and lift the weapon up level with the ground and hold it. :x

Never did rifle drill in 21 tho' - at least not with the SLR. Only formal parade we ever did was the opening of the Royal Academy (well - we were the Artists Rifles) and that was done using the silenced 9mm SMG AKA the Apache. I think that ceremony has been canned now due to security issues!


The L1A1 SLR was used in the field sans carrying handle and sling swivels and for us wounding was not really an option. Encounters with "the other side" would have meant either those encountered were down permanently or - rarely - were taken alive for interrogation. The mod to the sear was known, frowned on but done. The other one of using the LMG mags was not so good. Mainly because the springs in the LMG mag were too weak as the LMG was gravity fed as opposed to the SLR's force fed mechanism but also because it was a touch too long and when firing from the prone position the bottom of the mag would hit the ground - further compounded by having two mags taped together as some did.

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  • 1 year later...

most countries produced a 105mm field gun (notwithstanding how they described the gun, e.g by wieght of the round or calibre in inches, etc). The notable exception was the Swiss Army (whose main weapon now appears to be a knife ;o) which developed a 104mm gun.

In the same way, most countries uses now the 5,56mm NATO ammunition for their assault rifles. But Switzerland uses 5,6mm (0,04mm that make the difference). Swiss assault rifles have been made in order they can fire the 5,56 mm as well, but US M16 or french FAMAS cannot fire the swiss 5,6 mm. And with his former assault rifles, Switzerland did use 7,5 mm that is still in use for machine-guns. Switzerland has many weapon manufacturers and a great history in making weapons. Swiss army ever used Swiss made weapons as main individual weapons, however they used american and german equipment as well, like Browning machine-guns or Heckler & Koch sub machine-guns.


7,62 mm NATO standard is still largely used with the AK47 assault rifle around the world.


Swiss army knife is the main weapon against bred and cheese only. :-D

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Just to throw a curve :-D up till about 1918 the Russians used a measurement called a 'line' about 1/10 of an inch for measurement. Strictly the case length should also be included. 7.62x51 being NATO standard. Russian is normally shorter 7.62x49 if memory serves. So Russian ammo will fit NATO but not other way round :dunno: Artillery is also described by the calibre x the multiple of calibre to barrel length.

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Also the Soviet 7.62mm round is rimless whereas the NATO 7.62mm round has a rim that the roiund:


A) Seats on in the chamber




B) Is used by the extractor claw to eject the round.


Always seemed typical of the military that the other side could use our captured rounds but we couldn't use theirs.... :dunno: :dunno:

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Russia uses 2 types of 7.62 rounds. rimless 7.62 x 39 for the AK47 range and the belt fed MGs such as the MKT/PKM etc use a rimmed 7.62 x 54R (R = Rimmed), none of these rounds are compatible with NATO as NATO are classified as 7.62x51mm.



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