Turret weight vs calibre length

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Billy
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Turret weight vs calibre length

Post by Billy » Tue Aug 25, 2020 1:52 pm

Found it interesting that, in one of the comments on the forum mentioned something that got me thinking and made me look into this topic that may at first sight not be consequential to actually have rather large impacts to overall design.

So what I've found is the greater the barrel length in calibres the greater counter weight is needed to balance it, both on the barrel and the turret itself, and also the barrel needing extra stiffness from whipping and droop. All costing extra mass. A good example of this is Bismarcks long 52cal barrel, although others seem to define it at 47. It's turrets are large and the barrel is about the weight of most 16 inch barrels. A good example is the American turrets on going from 45 cal to 50. The difference in weight for this example was 1435 to 1730 tons. Or about 20% heavier. Noticed similar weight increases in other vessels like the British 12 inch and German 11 inch, but they had smaller circa 10% weight differences.

One then has to ask what consequences would this have. Well the Japanese 45 cal 16 inch turret was slightly lighter and carried more muzzle energy than Bismarcks 15 inch 52 cal. One can go to extremes and look at the older Italian 15 inch 40 cal which had a turret weight of only 550 tons. Nearly half the weight of Bismarcks turrets of 1056 tons. The first world war German Baden at 45 cal was around 850 tons, but in its original form before its charge was dropped of high velocity had a rather large muzzle energy too. The cost of all of this was a loss I have guestimmated or averaged at around 15fps per cal.

Billy
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Re: Turret weight vs calibre length

Post by Billy » Tue Aug 25, 2020 2:10 pm

So what does this all mean. Using the Italian 15/40 as an example. If fired the lighter she'll it would still be doing around 2550 fps, on the rather small charge of around 150kg cordite and a large barrel life. One could trade the barrel life for increased velocity. One could also up the calibre to a large 16 in, and have a lightweight turret throwing a powerful shell at reasonable velocities, almost like a carbine version.

There are other advantages aswell. The barrel is inherently stiffer being shorter, hence potentially more accurate also needing less stiffness to counter droop and being less inclined to whip. Also barrel tip velocities would be reduced with ship roll and barrel continues aim motors won't need to be as large. Leading to an otherwise excellent ballance. See the british 15/42 was very robustly built with high safeth factors, being able to fire with a cracked liner and was one inch wider than the simlilarly built Japanese 16 wire wound guns. They and potentially could've been bored to 16in and been approx 40 cal long. The size of their supercharges were about the right size to propel a Rodney type light shell to approx 2600 fps and barrel life of I'm guessing 250rpg and some modification of magazine supply. Extra weight of shells being accommodated by less of a magazine supply for no extra weight of ship. End result would be a much more powerful battery for no extra weight in these ships.

Billy
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Re: Turret weight vs calibre length

Post by Billy » Tue Aug 25, 2020 2:11 pm

So what does this all mean. Using the Italian 15/40 as an example. If fired the lighter she'll it would still be doing around 2550 fps, on the rather small charge of around 150kg cordite and a large barrel life. One could trade the barrel life for increased velocity. One could also up the calibre to a large 16 in, and have a lightweight turret throwing a powerful shell at reasonable velocities, almost like a carbine version.

There are other advantages aswell. The barrel is inherently stiffer being shorter, hence potentially more accurate also needing less stiffness to counter droop and being less inclined to whip. Also barrel tip velocities would be reduced with ship roll and barrel continues aim motors won't need to be as large. Leading to an otherwise excellent ballance. See the british 15/42 was very robustly built with high safeth factors, being able to fire with a cracked liner and was one inch wider than the simlilarly built Japanese 16 wire wound guns. They and potentially could've been bored to 16in and been approx 40 cal long. The size of their supercharges were about the right size to propel a Rodney type light shell to approx 2600 fps and barrel life of I'm guessing 250rpg and some modification of magazine supply. Extra weight of shells being accommodated by less of a magazine supply for no extra weight of ship. End result would be a much more powerful battery for no extra weight in these ships.

Billy
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Re: Turret weight vs calibre length

Post by Billy » Tue Aug 25, 2020 2:12 pm

Sorry about the double post. Internet seems slow today.

Steve Crandell
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Re: Turret weight vs calibre length

Post by Steve Crandell » Tue Aug 25, 2020 8:47 pm

I had a little trouble following your conclusion. Are you suggesting that it's better to have a short barreled gun than a long barreled one?

It's all about muzzle velocity with the same shell. The longer guns also have larger chambers to accomodate more propellant. If you try to use the same amount or more propellant in a short barrel you end up with a lot of wasted energy because the shell doesn't have enough time to accelerate up the to desired speed in a short barrel. Anyway, larger powder chambers required a stronger gun, so of course it gets heavier.

Sometimes a turret got heavier because it carried more armor, although longer guns did require more counterweight at the back of the turret, usually achieved by increasing armor thickness there.

The Germans did favor lighter shells with increased velocity. With flatter trajectories you have a larger target danger space and theoretically more hits. Higher velocities penetrate more armor.

German turrets were unusually long because their loading arrangement involved most of the powder charge being contained in a long powder case, and this required a longer turret for the powder hoist.

paul.mercer
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Re: Turret weight vs calibre length

Post by paul.mercer » Thu Aug 27, 2020 9:24 am

Thanks for that reply Steve,
A quick question, if one reduces this to revolver calibres it seemed to me (when we were allowed t own them!) that a short barreled pistol ofen left a small amount of unburned powder on the firing point particularly when using magnum loads whereas a 6 ot 7" barrel burned the powder much better,
(using 'factory' cartridges) this could be reduced by using a faster burning powder in say a 4" barrel, so my question is,was there such a thing as a faster burning charge to naval guns with shorter barrels?

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Re: Turret weight vs calibre length

Post by Steve Crandell » Thu Aug 27, 2020 4:42 pm

paul.mercer wrote:
Thu Aug 27, 2020 9:24 am
Thanks for that reply Steve,
A quick question, if one reduces this to revolver calibres it seemed to me (when we were allowed t own them!) that a short barreled pistol ofen left a small amount of unburned powder on the firing point particularly when using magnum loads whereas a 6 ot 7" barrel burned the powder much better,
(using 'factory' cartridges) this could be reduced by using a faster burning powder in say a 4" barrel, so my question is,was there such a thing as a faster burning charge to naval guns with shorter barrels?
Hi Paul,

I honestly don't know the answer to that. I have done some reloading with revolvers, and while what you say is true, you still don't have as much time to accelerate the bullet when using a shorter barrel. I guess it would be possible to get the same muzzle velocity with a huge frame and large case bullet, it obviously would still have less performance than a longer barrel would give you with both using optimal powder for their length. Besides not breaking your wrist in the process, LOL.

I guess the extreme short barrel example is a mortar, and those were used in fortifications, at least in the USA. They would be devastating if they hit, but your target would have to be pretty predictable to get hits on it; long flight time and small danger space. Don't have any idea what kind of dispersion they had.

Lots of people own pistols of all types here in the USA. Whether that's a good idea or not is a political thing, but it is what it is.

Bill Jurens
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Re: Turret weight vs calibre length

Post by Bill Jurens » Thu Aug 27, 2020 9:08 pm

A few quick observations:

There is little advantage to improved tube stiffness except at very short ranges. At longer ranges, it hardly matters at all.

So far as weight vs caliber is concerned, it's safe -- as a rule of thumb -- to assume that weight is proportional to the cube of the caliber.

It's easy to adjust the propellant web and quantity to compensate for differences in tube length or projectile travel, so this would have been done automatically.

In general, for constant initial energy input, i.e. muzzle energy, the heavier the shell, the more kinetic energy will be delivered to the target, regardless of range.

Bill Jurens

paul.mercer
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Re: Turret weight vs calibre length

Post by paul.mercer » Tue Sep 01, 2020 9:17 am

Hi Steve and Bill,
Thanks for your replies,I'm going a bit off topic here, but perhaps you could help me understand a bit more about reduced charges and super charges.
Am I right in thinking that, like most guns a large naval gun would have a chamber and once the shell had been rammed home that chamber would be filled by bags of cordite and i presume (rightly or wrongly!) that it must be filled completely. So if a reduced charge or a super charge was used would there be less or more cordite in the bag or would it be a less or more powerful form of cordite? Also, what sort of difference would both these charges make to the range -assuming a 15" gun?
Sorry if I haven't put this question very well.

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Re: Turret weight vs calibre length

Post by Bill Jurens » Tue Sep 01, 2020 7:26 pm

Good questions. Generally, the chamber is not filled completely. Even if one crammed the bags in by force, there would still be considerable 'empty' volume left, as (for example) single perforated grains -- basically thick tubes -- still leave the entire internal volume of the grain, and the space between the grains, unoccupied. The ratio between the actual amount of propellant, usually by weight, in the gun, vs the theoretical volume of the chamber is usually referred to as the 'loading density' or some near variant.

Generally, all propellant was stored in identical bags with identical propellant. "Reduced charges" were usually created by simply leaving one (or more) bags out of a load. As the loading density and the grain size are usually nominalized for the most efficient performance with a full load, leaving out a bag usually reduces the efficiency of a gun by a bit, but not by much, and -- because the loading is reduced, there is usually little concern over inappropriate chamber pressures, which usually go down rather than up, so the gun is -- at least theoretically -- 'safer'.

It's very difficult to generalize on the effects of a reduced charge vs a full charge, as these effects tend to vary with range, i.e. with angle of departure, and also because what constituted a reduced charge would vary from gun-to-gun. As a quick example, however, for the British 15" a full charge load at 20 degrees angle of departure would get you about 25,600 yards, whilst a 3/4 weight reduced charge would only get you 18,100.

Super charges represent an entirely different matter insofar as they imply a greater amount of energy delivered to the projectile, usually translated into a higher initial velocity. In these situations, because overall energy is closely related to maximum pressure, one must be careful not to overstress the gun. Supercharges could be made by increasing the propellant weight, changing propellant composition, or adjusting grain size, often in combination.

Hope this helps...

Bill Jurens

Steve Crandell
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Re: Turret weight vs calibre length

Post by Steve Crandell » Wed Sep 02, 2020 6:04 am

If the supercharge the British used was safe (and I assume it must have been or they wouldn't have used it), why wasn't the supercharge used as the normal charge, since it produced more muzzle energy?

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Re: Turret weight vs calibre length

Post by Bill Jurens » Wed Sep 02, 2020 5:52 pm

Another good question. Probably because the additional wear and tear on the gun and mounting didn't justify the advantage except in unusual circumstances. To begin with, it's more difficult to design supercharges as they tend to be smaller in size than regular bag loads, i.e. for a five bag load, going to four bags (i.e. to 80% loading) is easier than going to six bags (i.e. to 120% loading). The factors of safety in guns, particularly where weight is an important issue, are just not that large, i.e one additional bag is just too much. One might 'push the envelope' 10% or so and still remain within tolerable limits. For a typical 15" caliber gun, a 10% increase in pressure is caused by about a 5.5% change in charge weight. That means an additional 'out of size' additional bag -- for a 400 pound load this would amount to one additional 22 pound bag. Inconvenient to store and handle. Alternatively, of course, one might increase the bag size a bit, from (say) four 110 pound bags to four 116 pound bags. But that's getting a bit big to manhandle. Or, one could go to five 88 pound bags, at some increase in stowage space.

That same change in charge weight might result in a 3.9% change in initial velocity. Assuming that the roughly 5% increase in kinetic energy at short ranges is negligible with respect to armor penetration, that means that the only real advantage might lie in increasing the range. A 4% change in initial velocity might increase the maximum range by about 7.5%, e.g. from c. 40,000 to 43000 yards, probably at some cost in the consistency of initial velocity, i.e. in a measurable loss in accuracy. And at that range, the time of flight is so long that chances of actually hitting a moving target are pretty much negligible anyway.

Designs are typically made not to operate at maximum capacity all of the time, but at something less than maximum capacity most of the time. although one's automobile might be capable of 180 km/hr, but it's probable that it never actually sees that speed during its entire twenty-year lifetime, and if it did, something would probably fail within 10 or 15 minutes of driving.

Bill Jurens

Steve Crandell
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Re: Turret weight vs calibre length

Post by Steve Crandell » Wed Sep 02, 2020 10:18 pm

Thanks for the detailed answer, Bill. I think I remember reading that supercharges increased bore wear quite a bit more than just the proportional increase in velocity.

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Re: Turret weight vs calibre length

Post by Bill Jurens » Thu Sep 03, 2020 2:15 am

That's true. The relationship between wear rate and initial velocity is extremely complex, depending upon the design of the driving band(s), projectile seating, gun caliber, propellant chemistry, and rate-of-fire, and usually must be treated on a case-by-case basis. In VERY rough terms, the following sort of average relationship -- if that word can be used at all in this context -- can be considered 'typical'.

% initial velocity = relative tube life
90 = 2.0
95 = 1.4
100 = 1.0
105 = .67
110 = .43

Bill Jurens

paul.mercer
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Re: Turret weight vs calibre length

Post by paul.mercer » Thu Sep 03, 2020 4:39 pm

Bill, Steve,
Thanks very much to you both.

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