Rifling twist in Artillery cannons

[Trickymissfit]

For readers, those 50 caliber 16" barrels were 800 inches long; 16 x 50 bore diameters. Almost 67 feet long.

looking at it this way:

* the 175mm gun (it was a rifle and not a howitzer) had a 32 foot long barrel, and at sea level was rated at 23 miles with a 147lb. projo that went faster that a 52 grain bullet out of an M16. The barrel had a measured 1.5" of droop in it, and when you shot the thing you could watch it whip around all over the place (not real accurate as well). The same gun at 2000ft above sea level shooting a zone three charge into an area that was at sea level was known to hit the 25 mile plus area (some say 27 miles) with a patteren that was almost three hundred yards in diameter. Barrels were good for about 80 zone three shots (powder charge is 5'7" long and about 12" in diameter). We had no serious way to allow for the barrel droop back then or even the heat build up.

Now we have a barrel that's 67 feet long with a 16" bore! That thing has to have a good bit of droop in it (sag), and the powder charge is probably on the scarey side!. Ad to this the fact that you have to actually add a counter weight to that breech area or better yet back side of the turret to keep the gun mount intact. Being as the projo was rocket propelled that would have helped tremondously in barrel life (with gun powder the breech alone would have been shot in fifty rounds). My guess was that they had a way to guide it as well. But in the end the gun mount would have been seriously over taxed to where it was gone in less than a year of heavy use. Those gun mounts are hand scraped and the fit is reasonably close (probably under .003" of being square). I'd have hated to been the unlucky devil that had to scrape the rotating surfaces, and knowing that in a year you'd be doing it again!
gary

 

[Kevin Thomas]

Gary,

The HARP gun that I mentioned was actually closer to 132' in length, being two 16" 50 cal barrels joined together. Very definate droop problems with all these designs, too, and most of Bull's guns used a series of stiffeners and reenforcing rods to accomodate that fact. His biggest project (the kne that got him killed) was the so-called "Supergun" he was working on for Saddam. That one was actually built right into a mountianside, laying along the slope of the hillside to support it.

Still seemed like a stupid idea to me, and personally, I think Bull just wanted to see what he could do here. From a tactical standpoint, they would have gotten one, maybe two rounds off before the Israeli Air Force turned it into scrap metal.

 

[Trickymissfit]

The German 75mmL/70 used on the Panther was one of the best anti tank guns used in the war, and was a threat to virtually any armor on the battlefield. Same round that was used in the PAK40 you mentioned as well, and quite different than the 75mm used on the PzKpfwIVs and Stugs throughout most of the war. Don't recall that specific quote from Cooper, but it sounds like something he said, or certainly would agree with. He was pretty bitter about the Sherman's performance in battle against the Panthers. I know of at least one instance where two(2) Shermans were taken out by one round from a Panther, the projectile passing cleanly through the first, and going on to penetrate the second Sherman behind it. That's some pretty impressive penetration in anyones book!

The taper bore guns you mentioned were the Gerlich series. They never really came to fruition, at least never to the claims that Gerlich made for them. Speer eventually got pretty fed up with him over the hype and lack of real results, a dangerous thing in Nazi Germany of that era. After the war, Gerlich got some attention by the US Army Ordnace Corps, but again, his results never quite reached the results that he claimed they would. Still, he came up with some pretty impressive performance for guns of that time. Still, as you said, by the time the Russians hit Berlin, the Germans were throwing everything they had (including the kitchen sink) at them. That was one helluva battle, and the city still bears some of the scars.

when you start looking at German anti tank guns you divide them into the PAK series and the KWK series; even though the guns are very similar if the calibers are the samething. The MK.IV used the KWK L43 and later the KWK L48 series. The L43 was very similar to the PAK 40 if memory is correct. The STUG's and Marders also used the PAK 40 series guns too. On paper the L48 with a tungsten cored APC round was actually a better penetrator than the 88mm round. But the 88mm round had a lot more shear power behind it. There were probably more tanks knocked out with an 88 than 75's in the end when you also take into use the frmer anti aircraft guns used against armor. The real differnces can be seen on film if you know what your looking at. The 75mm would crack the turret and kill everyone inside. The 88 would often simply blow the entire turret ring assmbly off the tank in the process. The Germans had far better gun sights than the Allies did, and could easilly engage a target a double the yardage that something like a T34 or IS2 could. (Otto Carrius said the IS2 was the best tank of the war by the way).

To give someone an idea about the range of a PAK40 one needs to know that they often made one shot kills at over 1500 yards, and I said made one that was 3300 meters (actually caught on film). Now another interesting aspect to this is concerning all the Russian tanks knockedout by JU87's shooting 37mm cannon! There has been an ongoing argument for years about wether the iL2 or the JU87 got more kills. My guess is the iL2 as they had much more of them. But per plane the JU87 was way out in front. (remember the weakest point on a tank is the top of the turret and the engine grates)

Had the war progressed into 1946, the Allies would have faced the new design "E" series tanks that actually very similar in design to the Abrams. The main guns varied from an even more powerfull 75mm to a massive 128mm cannon. The Brits tested one E75, and had nothing that would crack the armor. (they tested them with 17 pounders and 25 pounders. A 90mm on a Pershing would have been usless. Of course the Russians were very close to going into production with their T54 series tanks.
gary

 

[Bart B]

Now we have a barrel that's 67 feet long with a 16" bore! That thing has to have a good bit of droop in it (sag), and the powder charge is probably on the scarey side!. Ad to this the fact that you have to actually add a counter weight to that breech area or better yet back side of the turret to keep the gun mount intact. Being as the projo was rocket propelled that would have helped tremondously in barrel life (with gun powder the breech alone would have been shot in fifty rounds). My guess was that they had a way to guide it as well. But in the end the gun mount would have been seriously over taxed to where it was gone in less than a year of heavy use. Those gun mounts are hand scraped and the fit is reasonably close (probably under .003" of being square). I'd have hated to been the unlucky devil that had to scrape the rotating surfaces, and knowing that in a year you'd be doing it again!

USN's 16"/50 barrels did have droop. It was corrected for inside the MK 8 Rangekeeper with a simple cosine cam and whatever droop there was got put in the elevation gun order section of that fabulous mechanical computer. But the flat ring the turret circled on, called a roller path, was never hand scraped. It was turned as good as could be then set on the deck and welded in place. Once the turret was set on it, it stayed there forever; unless the ship capsized then it would just drop out and fall to the bottom as only gravity kept it in place. The gunners mate's could get to it, clean and lube it so it worked well and lasted a long time.

Note the turrets had 18-inch thick faces and a bit less on their tops and sides. If you look at one, their back end sticks way out behind the roller bearings on the round platform they move on. The weight of the barrels is well balanced. But the plane of each of the three turrets "roller paths" wasn't parallel with each other. Unless this was corrected for, each turret's guns would have a different elevation angle for a given elevation gun order. This problem was solved with a "deck tilt correction" adjustable gear box in each turret. A fire control technician (USN abbreviation FT, whom I was for 22 years in the USN) in the main battery director would put its sights on the horizon, the director signals for bearing and elevation would be sent to the rangekeeper in main battery plot where the FT operating it would set the gun order correction section to zero. The turret barrels would then point where the director pointed. Everyone was on sound powered telephones and when the FT in the director sounded "Mark" as the director sight crosshairs crossed the horizon on the up roll, the FT in the turret looking through a bore scope in the breech would see where it was. If it wasn't dead on when he heard the "Mark" he had to adjust the deck tilt corrector a bit. This was repeated every 10 degrees of the turret's firing arc, and on each turret, too. After 'twas all done, each turret would have a chart with its high path point and each 10 degrees correction needed put in the deck tilt corrector. Looking at these charts made it easy to see how each roller path had its own high point and amount of correction needed. This "bore sighting" process took a while and we all prayed for calm weather so it would be easy to do. And it was checked and corrected for a few times each year 'cause big ships bend a bit from use and heavy seas. 8" and 6" turrets as well as 5" gun mounts all had to do this.

The rangekeeper also had a parallax corrector for each turret on board. As the turrets center of rotation was different distances in yards from the director, each one needed different corrections.

Barrel life, finally, was rather short. Considering a full charge for a 16"50 was six 110-pound bags of powder; a reduced load had 4 bags, there was a lot of wear at the breech end. Each with its own packet of black powder on its rear end to enhance burning. In their first years starting in the late 1930's, barrel life was about 250 rounds before the throat had eroded to its accuracy limits. A change in the powder in the early 1940's increased it up to 350 rounds. But after each 50 to 75 rounds, the liner with the rifling in it would be pushed forward enough that it's muzzle stuck out beyond the rest of the barrel. When its protrusion was up to 1/4th inch, it got turned off back flush with the muzzle. A special hand turned tool was clamped on the muzzle to turn off the extended liner back to the rest of the barrel. After refacing that liner 4 times, it would be replaced when it stuck out about 1/4th inch. It took two days of hard work by several people using large machines to pop that liner out then replace it with a new one. The old liner came out the back end of the turret.

FT's also had computers to calculate muzzle velocity using the powder lot's tempurature curves A bore erosion gage was put in the breech and the reading compared with known wear curves vs velocity loss. This was all added together and the muzzle velocity settings were cranked into that mechanical rangekeeper.

Not a bad way at all to set stuff right. The battleship New Jersey's Fire Control Smooth Log (detailed historic data of how the guns performed) I got to see in 1968 listed their first-round miss distance off the North Vietnamese coast at 90 meters. Pretty good accuracy for those big guns

 

[Loner]

some nice picks of the big rail guns.

Big Guns of the Great War

 

[Iron Worker]

The German 75mmL/70 used on the Panther was one of the best anti tank guns used in the war, and was a threat to virtually any armor on the battlefield. Same round that was used in the PAK40 you mentioned as well, and quite different than the 75mm used on the PzKpfwIVs and Stugs throughout most of the war. Don't recall that specific quote from Cooper, but it sounds like something he said, or certainly would agree with. He was pretty bitter about the Sherman's performance in battle against the Panthers. I know of at least one instance where two(2) Shermans were taken out by one round from a Panther, the projectile passing cleanly through the first, and going on to penetrate the second Sherman behind it. That's some pretty impressive penetration in anyones book!

The taper bore guns you mentioned were the Gerlich series. They never really came to fruition, at least never to the claims that Gerlich made for them. Speer eventually got pretty fed up with him over the hype and lack of real results, a dangerous thing in Nazi Germany of that era. After the war, Gerlich got some attention by the US Army Ordnace Corps, but again, his results never quite reached the results that he claimed they would. Still, he came up with some pretty impressive performance for guns of that time. Still, as you said, by the time the Russians hit Berlin, the Germans were throwing everything they had (including the kitchen sink) at them. That was one helluva battle, and the city still bears some of the scars.

How would those WW2 German anti tanks rounds perform on our modern day tanks ? Like our Abrams ? I guess no one really knows if the type of armor is classified ?

 

[the gman]

How would those WW2 German anti tanks rounds perform on our modern day tanks ? Like our Abrams ? I guess no one really knows if the type of armor is classified ?

I'm a former Brit Army gunfitter which means I worked on anything above 30mm in bore diameter and I was a Chobham Armor repair tech as part of that. Modern armor on Abrams, Challenger 1 & 2 MBT and many other western MBT's are all derived from Chobham. The exact makeup of the armor is classified and despite living in the US these days, I'm not about to reveal the secrets I was entrusted with.

Having said all that, when I did the repair course, we were shown many examples of the armor with all manner of anti-tank projectiles fired at it. IIRC, (and I'm going back 15 years) an AP round from an early L7 105mm round was stuck in a sample of what would be the frontal armor of a Abrams/Challenger.

We saw the results of many other rounds fired at the armor and many of them vastly exceeded the kinetic energy of the WW2 rounds. It was extremely impressive to see just how much punishment the armor could withstand. With the addition of bolt on applique packs and reactive armor, even modern AT projectiles (not to mention the old WW2 stuff) don't stand much of a chance against Chobham.

FYI, the Brits still use a rifled barrel as it enables the tank to accurately fire the HESH round that is preferred over the HEAT round of a smoothbore. Sadly, the 120mm rifled ammo is out of production in the UK and so moving to a smoothbore is somewhat inevitable. Very interesting discussion, especially as regards the steps involved in firing the large naval guns.

 

[Trickymissfit]

USN's 16"/50 barrels did have droop. It was corrected for inside the MK 8 Rangekeeper with a simple cosine cam and whatever droop there was got put in the elevation gun order section of that fabulous mechanical computer. But the flat ring the turret circled on, called a roller path, was never hand scraped. It was turned as good as could be then set on the deck and welded in place. Once the turret was set on it, it stayed there forever; unless the ship capsized then it would just drop out and fall to the bottom as only gravity kept it in place. The gunners mate's could get to it, clean and lube it so it worked well and lasted a long time.

Note the turrets had 18-inch thick faces and a bit less on their tops and sides. If you look at one, their back end sticks way out behind the roller bearings on the round platform they move on. The weight of the barrels is well balanced. But the plane of each of the three turrets "roller paths" wasn't parallel with each other. Unless this was corrected for, each turret's guns would have a different elevation angle for a given elevation gun order. This problem was solved with a "deck tilt correction" adjustable gear box in each turret. A fire control technician (USN abbreviation FT, whom I was for 22 years in the USN) in the main battery director would put its sights on the horizon, the director signals for bearing and elevation would be sent to the rangekeeper in main battery plot where the FT operating it would set the gun order correction section to zero. The turret barrels would then point where the director pointed. Everyone was on sound powered telephones and when the FT in the director sounded "Mark" as the director sight crosshairs crossed the horizon on the up roll, the FT in the turret looking through a bore scope in the breech would see where it was. If it wasn't dead on when he heard the "Mark" he had to adjust the deck tilt corrector a bit. This was repeated every 10 degrees of the turret's firing arc, and on each turret, too. After 'twas all done, each turret would have a chart with its high path point and each 10 degrees correction needed put in the deck tilt corrector. Looking at these charts made it easy to see how each roller path had its own high point and amount of correction needed. This "bore sighting" process took a while and we all prayed for calm weather so it would be easy to do. And it was checked and corrected for a few times each year 'cause big ships bend a bit from use and heavy seas. 8" and 6" turrets as well as 5" gun mounts all had to do this.

The rangekeeper also had a parallax corrector for each turret on board. As the turrets center of rotation was different distances in yards from the director, each one needed different corrections.

Barrel life, finally, was rather short. Considering a full charge for a 16"50 was six 110-pound bags of powder; a reduced load had 4 bags, there was a lot of wear at the breech end. Each with its own packet of black powder on its rear end to enhance burning. In their first years starting in the late 1930's, barrel life was about 250 rounds before the throat had eroded to its accuracy limits. A change in the powder in the early 1940's increased it up to 350 rounds. But after each 50 to 75 rounds, the liner with the rifling in it would be pushed forward enough that it's muzzle stuck out beyond the rest of the barrel. When its protrusion was up to 1/4th inch, it got turned off back flush with the muzzle. A special hand turned tool was clamped on the muzzle to turn off the extended liner back to the rest of the barrel. After refacing that liner 4 times, it would be replaced when it stuck out about 1/4th inch. It took two days of hard work by several people using large machines to pop that liner out then replace it with a new one. The old liner came out the back end of the turret.

FT's also had computers to calculate muzzle velocity using the powder lot's tempurature curves A bore erosion gage was put in the breech and the reading compared with known wear curves vs velocity loss. This was all added together and the muzzle velocity settings were cranked into that mechanical rangekeeper.

Not a bad way at all to set stuff right. The battleship New Jersey's Fire Control Smooth Log (detailed historic data of how the guns performed) I got to see in 1968 listed their first-round miss distance off the North Vietnamese coast at 90 meters. Pretty good accuracy for those big guns

you should recognize my call sign from down Tam Key way.

Arty pretty much does the samething, but calls it out differently. All guns are registered (you all will know this as zeroing), and the sights are then calibrated to the actual target(s) impact. Then reshot over till all comes out right. Then the base piece is redone again to set up a corrected impact pattern. After that everything comes off the base piece even though the others maybe as much as 250 yards away. The base piece register is checked weekly, but the rest are not unless something is not right. Anytime a barrel, breech, or the Pentell is changed the howitzer is rezeroed.

That red cap on the end of the lowest numbered powder charge is the samething as flash powder used in old time photgraphry. It's not really black powder but an extremely fast burning powder. Not real sure when they made the complete switch to nitro cellulose powders, but it must have been in the 1940's or earlier. I shot powder lots made in the 1940's that were nitro cellulose. The rounds hadn't changed mush as well, because I shot lots of projos that had 1944 dates on them in 155mm and 8". I also blew a 16" round in place that you could still read the date on it, and it was 1944. As for the red cap, I've cut many of them open in my day. But there has been a long going rumor that all arty uses nothing but black powder. I never saw anything use the stuff. All the 175 stuff was fairly new manufacture, and never saw the insides of a powder bag to see what they were using. I know it was some pretty hot stuff!

I never calculated it out, but when I was imprisioned in the FDC bunker (about 60 days) the rule of the thumb was that one mil of error equaled one hundred yards at ten thousand yards. That figure seem kinda large at the time, but guys in there were smarter than I was. As for temperature compensation; they had a factor number they figured in there as the temp rose in the air and also in the powder bunker. Temps were taken every four hours like clock work.
I did most of my stuff on 155 howitzers, and the barrels never had a temperature factor used in them (I've seen barrels glow in the dark!). In an arty barrel they use a factor number that varies by the powder charge. A charge seven being a number one, but a charge five green bag is about point three if I remember right. When you reach the ten thousand number they change barrels. But if the impact zone from a certain barrel starts to show error; they will go ahead and change it out anyway. ($$$) A 175mm gun has roughly an 80 round barrel count. I don't have any idea what an 8" is (or was), but was probably very similar to a 155. The 8" was known as the single most accurate cannon used in the U.S. military. It could tag a garbage can at max range round after round, and I've seen them do this more than a few times. Virtually all barrels except for the 175 gun will go thru three to four breeches in their lifetime (105's maybe not). The breech on a 155 takes a lot of beating, and after awhile becomes a serious chore to open and close it. But that's all about to change!
gary

 

[Loner]

Great thread guys, I am really enjoying the info you big gun guys are writing. Never
seen anything like the details you are sharing. Thanks.

 

[Trickymissfit]

How would those WW2 German anti tanks rounds perform on our modern day tanks ? Like our Abrams ? I guess no one really knows if the type of armor is classified ?

not all that well. There are places that can be hit, and can knock it out. But in the hull or frontal area it's not gonna happen. I've seen actual film footage of the turret on an M1 IP taking a hit from a naval five inch gun using APC. The round did not penetrate the fighting compartment. On the otherhand there is a new round that will go in there like a punch press at 4000 yards. I've seen the actual armor blank shot with it, and it looks like somebody cut a pretty 6" diameter laser cut hole (100lb. projo @ 4200fps @ 2000yards).

In WWII the heaviest armor used was on a JagedTiger, and even the 100mm and 122mm Russian stuff wouldn't crack the hulls. But on a Tiger one the 100mm round would fairly consistently do the job under 800 yards. A Tiger II would have to have been a little closer. Yet the 88mm round from a Tiger would crack the hull on an IS2 at those ranges. A lot of this has to do with just how square the impact is with the target, and of course yardage. I don't think the Russians ever used any serious shaped charge or tungsten cored rounds. The western Allies used some very intricate shaped charge rounds, but for the most part of it the guns lacked the velocity to get the job done over 500 yards. The best of them being the 17 pounder and the 90mm. (I think the 17 pounder was equale to about 85mm). The M1 reverts alot of it's design concepts back to the welded dove tail construction first used on the Panther, but with much better quality armor plate and a few other features. The Abrams and the ChallangerII are both very well designed tanks that have proven combat records.
gary

 

[Trickymissfit]

I'm a former Brit Army gunfitter which means I worked on anything above 30mm in bore diameter and I was a Chobham Armor repair tech as part of that. Modern armor on Abrams, Challenger 1 & 2 MBT and many other western MBT's are all derived from Chobham. The exact makeup of the armor is classified and despite living in the US these days, I'm not about to reveal the secrets I was entrusted with.

Having said all that, when I did the repair course, we were shown many examples of the armor with all manner of anti-tank projectiles fired at it. IIRC, (and I'm going back 15 years) an AP round from an early L7 105mm round was stuck in a sample of what would be the frontal armor of a Abrams/Challenger.

We saw the results of many other rounds fired at the armor and many of them vastly exceeded the kinetic energy of the WW2 rounds. It was extremely impressive to see just how much punishment the armor could withstand. With the addition of bolt on applique packs and reactive armor, even modern AT projectiles (not to mention the old WW2 stuff) don't stand much of a chance against Chobham.

FYI, the Brits still use a rifled barrel as it enables the tank to accurately fire the HESH round that is preferred over the HEAT round of a smoothbore. Sadly, the 120mm rifled ammo is out of production in the UK and so moving to a smoothbore is somewhat inevitable. Very interesting discussion, especially as regards the steps involved in firing the large naval guns.

I worked in the Abrams drive trane development, and at one time was doing some work on the Challanger drive trane (They kept the David Brown stuff instead). I watch the hulls evolve and now they are vastly different, but still the samething!

I never worked with Chobham armor in person, and really wasn't allowed to see them cut it when I made visits to Lima. I actually know of no one that has ever saw it being done! The Russians were the first to come up with the concept, but could machine it. Then the British got it, and it actually layed around for quite awhile with no idea how to work with it. I think it was either valenite or a combination of Valenite and Kennmetal that developed cutting tools to do the job (still very secretive). I do know that the folks at Valenite were only allowed to see the metal shavings in a remote room far from the work area. They's look at them and make changes, and then have them try again and again. I kinda think that they started out using tooling developed for hestalloy and waspalloy that we developed where I worked. Then made a ton of changes in the concept. That part never bothered me as it looked like it's been easier to do with a laser or electron beam. What I never understood was how they welded all that stuff together, and I've been in there where the welding was going on! Anyway the cat's outta the bag as everybody seems to have the intellectual property now.
gary

 

[Iron Worker]

Fascinating stuff guys ! Glad I posted OQ .

 

[the gman]

I worked in the Abrams drive trane development, and at one time was doing some work on the Challanger drive trane (They kept the David Brown stuff instead). I watch the hulls evolve and now they are vastly different, but still the samething!

I never worked with Chobham armor in person, and really wasn't allowed to see them cut it when I made visits to Lima. I actually know of no one that has ever saw it being done! The Russians were the first to come up with the concept, but could machine it. Then the British got it, and it actually layed around for quite awhile with no idea how to work with it. I think it was either valenite or a combination of Valenite and Kennmetal that developed cutting tools to do the job (still very secretive). I do know that the folks at Valenite were only allowed to see the metal shavings in a remote room far from the work area. They's look at them and make changes, and then have them try again and again. I kinda think that they started out using tooling developed for hestalloy and waspalloy that we developed where I worked. Then made a ton of changes in the concept. That part never bothered me as it looked like it's been easier to do with a laser or electron beam. What I never understood was how they welded all that stuff together, and I've been in there where the welding was going on! Anyway the cat's outta the bag as everybody seems to have the intellectual property now.
gary

Not exactly out of the bag as the armor is much more than just the outer shell that shows it's face to the world; lotsa stuff going on under the surface. In addition, I signed a piece of paper called 'The Official Secrets Act' which has it's roots in the early 20th century and that document applies to me until the day I die. I have no desire to be arrested should I blab and go back to the UK for a visit, even though I am now a US citizen. The Brits take their secrets pretty seriously but I also have no intention of sharing anything that may aid some scumbag terrorist somewhere in figuring out a way to penetrate the armor.

On another note, the mil is an angular measurement and is very simple to work with, if you understand metric measurements. One mil subtends 1 meter at 1000 meters with 6400 mils in a circle. So if you are calling in arty and you are 10,000 meters from the firing point, need the POI to shift 100 meters forward and 200 right, s'real easy to call that out. Compared to seconds, minutes and degrees at least!

 

[Bart B]

On another note, the mil is an angular measurement and is very simple to work with, if you understand metric measurements. One mil subtends 1 meter at 1000 meters with 6400 mils in a circle. So if you are calling in arty and you are 10,000 meters from the firing point, need the POI to shift 100 meters forward and 200 right, s'real easy to call that out. Compared to seconds, minutes and degrees at least!

1/6400th of a circle equals 3.375 minutes of angle (trig, not shooting).That's 0.98175 of a yard (or meter) at 1000 yards (or meters). The amount's close to .001 of the range but exactly, its .00098175.

There's four different standards for a mil. It's 1/6000th, 1/6283th, 1/6300th or 1/6400th of a circle depending on whose standard you use. When in the USN and we did shore bombardment or surface target exercises, we used 1/6283 of a circle, or 0.00100003 of the range. Close enough to 1 yard at 1000. Both the observer's near the target and the ship's plotting room crew's mil spot converters were the same.