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Old 08-20-2019, 03:51 PM   #1
Michael Thayne
 
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Default [High-Tech] Understanding the practical rate of fire for a cannon.

I'm trying to get a better grip on how to interpret GURPS stats for crew-served weapons, particularly how to translate statistics like RoF and Shots into a practical rate of fire. Specifically:
  • If you have a cannon with something like Shots 1(4) crewed by a gunner and a loader, can the gunner take Aim maneuvers while the loader is taking a series of Ready maneuvers to load the weapon? Or does the gunner have to wait until the loader is done loading before the gunner can start taking aiming?
  • What does the fractional RoF for the Motovilikha D-81TM (the big Russian tank gun) in High-Tech mean? Does it mean it takes eight maneuvers for the gunner to fire? Or just that the gunner has to wait 7 seconds between attacks for the autoloader to reload the gun? In the latter case, can the gunner take Aim maneuvers while the autoloader is doing its thing?
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Old 08-20-2019, 04:55 PM   #2
AlexanderHowl
 
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Default Re: [High-Tech] Understanding the practical rate of fire for a cannon.

No, loaders have to get in the way of the gunner and move the cannon to facilitate loading.
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Old 08-20-2019, 05:08 PM   #3
Michael Thayne
 
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Default Re: [High-Tech] Understanding the practical rate of fire for a cannon.

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Originally Posted by AlexanderHowl View Post
No, loaders have to get in the way of the gunner and move the cannon to facilitate loading.
This seems right for muzzle loaders, but would it be true of a breech loader? I particularly wonder if it would apply when you're talking about, say, a WWII-era tank.
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Old 08-20-2019, 05:11 PM   #4
Ulzgoroth
 
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Default Re: [High-Tech] Understanding the practical rate of fire for a cannon.

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Originally Posted by AlexanderHowl View Post
No, loaders have to get in the way of the gunner and move the cannon to facilitate loading.
That's certainly not going to be true in all cases. You could easily* lay out a cannon such that the loader can work without getting in the gunner's space or moving the gun.

* May be less easy in cramped environments or when the ammunition is very heavy.

My impression is that the usual practice of modern US tank gunnery doesn't has the gunner stay on their scope during the reloading, but I could be wrong about that.

There are definitely cannons where the loader can feed more ammunition while the gunner is shooting - but those are of course automatic cannons where the loader is adding ammunition to an automatic feeder rather than directly loading the breach.

In a turret, there should be little problem with doing horizontal traversal while reloading, since the loader will be inside the traversing body. Elevation adjustment could be a problem, since you're normally moving the gun relative to the turret when you do that. OTOH the adjustments there are usually small.

Addendum: Automatic loading assists often require the gun go to a particular elevation to work. That would probably interfere with aiming, unless the gunner's sight somehow disengages from the gun and then re-aligns. Which seems like it probably wouldn't be accurate.
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Last edited by Ulzgoroth; 08-20-2019 at 05:14 PM.
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Old 08-20-2019, 06:30 PM   #5
Fred Brackin
 
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Default Re: [High-Tech] Understanding the practical rate of fire for a cannon.

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Originally Posted by Michael Thayne View Post
This seems right for muzzle loaders, but would it be true of a breech loader? I particularly wonder if it would apply when you're talking about, say, a WWII-era tank.
Look at the weights involved. The shells for the guns for the Panzer IV and the Sherman weight 23 and 24 lbs. So first that weight slams into the gun and then the breech (which should be a significant percentage of the gun's 1000 lb+ weight) thuds home. These motions probably did make the gun move in response and should have made a coaxial sight move too.

You wouldn't be able to start aiming on the turn after the gun fired because the tank rocks on its' treads from the recoil. For that matter, anyone who could concentrate through the noise of firing ought to have Unfazeable at least.
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Old 08-20-2019, 06:46 PM   #6
Anthony
 
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Default Re: [High-Tech] Understanding the practical rate of fire for a cannon.

For guns listed in High-Tech, I would say you aren't going to do what GURPS calls an aim maneuver, though you could certainly spend the reload time updating your firing solutions so you know the bearing and elevation you want for your next short.
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Old 08-20-2019, 08:05 PM   #7
Michael Thayne
 
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Default Re: [High-Tech] Understanding the practical rate of fire for a cannon.

Quote:
Originally Posted by Fred Brackin View Post
Look at the weights involved. The shells for the guns for the Panzer IV and the Sherman weight 23 and 24 lbs. So first that weight slams into the gun and then the breech (which should be a significant percentage of the gun's 1000 lb+ weight) thuds home. These motions probably did make the gun move in response and should have made a coaxial sight move too.
Does the same logic apply for more recent designs with autoloaders? (After posting the OP I noticed the autoloader rules are somewhat clarified in the High-Tech errata, but it's still unclear if you can Aim while the autoloader is running.
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Old 08-20-2019, 08:17 PM   #8
Fred Brackin
 
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Default Re: [High-Tech] Understanding the practical rate of fire for a cannon.

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Originally Posted by Michael Thayne View Post
Does the same logic apply for more recent designs with autoloaders? (After posting the OP I noticed the autoloader rules are somewhat clarified in the High-Tech errata, but it's still unclear if you can Aim while the autoloader is running.
Modern tanks rock on their tracks probably even more than WWII models and only the T-72 family uses an autoloader. It may stay that way too as the T-72 autoloader makes the inside of the turret into a deathtrap if it gets penetrated. The gunner and commander are surrounded by over a thousand lbs of naked nitrocellulose.

You might see common autoloaders in the future if you get totally unmanned turrets. separated from the hull by a firewall. Aiming would be electronic then of course but the tank still obeys Newton's 3rd law.
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Old 08-20-2019, 08:54 PM   #9
Ulzgoroth
 
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Default Re: [High-Tech] Understanding the practical rate of fire for a cannon.

Quote:
Originally Posted by Fred Brackin View Post
Look at the weights involved. The shells for the guns for the Panzer IV and the Sherman weight 23 and 24 lbs. So first that weight slams into the gun and then the breech (which should be a significant percentage of the gun's 1000 lb+ weight) thuds home. These motions probably did make the gun move in response and should have made a coaxial sight move too.
How do you imagine the gun being mounted that it would be able to move relative to the turret under those forces without breaking the training mechanism and effectively disarming the tank?
Quote:
Originally Posted by Fred Brackin View Post
Modern tanks rock on their tracks probably even more than WWII models and only the T-72 family uses an autoloader. It may stay that way too as the T-72 autoloader makes the inside of the turret into a deathtrap if it gets penetrated. The gunner and commander are surrounded by over a thousand lbs of naked nitrocellulose.

You might see common autoloaders in the future if you get totally unmanned turrets. separated from the hull by a firewall. Aiming would be electronic then of course but the tank still obeys Newton's 3rd law.
Lots of tanks other than the T-72 family use autoloaders. Aside from Russian tanks, they can be found in US light vehicles (Stryker MGS), as well as in Chinese, Japanese, French, and Korean main battle tanks.

It's not impossible to have an autoloader that draws from an isolated ammo compartment rather than putting the magazine in the fighting compartment, and reportedly some modern ones do. Cold-war era soviet models did have that issue, though.
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Old 08-20-2019, 10:12 PM   #10
Michael Thayne
 
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Default Re: [High-Tech] Understanding the practical rate of fire for a cannon.

Quote:
Originally Posted by Fred Brackin View Post
Modern tanks rock on their tracks probably even more than WWII models and only the T-72 family uses an autoloader. It may stay that way too as the T-72 autoloader makes the inside of the turret into a deathtrap if it gets penetrated. The gunner and commander are surrounded by over a thousand lbs of naked nitrocellulose.

You might see common autoloaders in the future if you get totally unmanned turrets. separated from the hull by a firewall. Aiming would be electronic then of course but the tank still obeys Newton's 3rd law.
I have no military experience but the significance of Newton's 3rd law isn't obvious to me. A 60 metric ton tank firing a 7 kilogram shell has about the same ratio of platform mass : projectile mass as a 75 kilogram hunter firing a 9 gram bullet. And I think similar logic would apply to how much chambering the round is going to throw off your aim. I admit there might be a disanalogy I'm missing.

(Also, maybe modern tanks do rock a lot from recoil, but if the tank stops rocking when the autoloader is only halfway done doing its thing maybe that gives you a few seconds to aim if the autoloader problem isn't really a problem?)
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