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Old 11-19-2019, 08:00 PM   #31
Ulzgoroth
 
Join Date: Jul 2008
Default Re: Different Gyroc Designs

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Originally Posted by Varyon View Post
A target 60 yards out will be reached in about 1/10th of a second by a typical (600 yards/second) rifle round. That becomes 1/5 s for 120 yards, 3/10 s for 180 yards, 2/5 s for 240 yards, and finally 1/2 s for 300 yards. At 60 yards, the bullet will drop about 2 inches, which isn't likely to make a difference unless you were aiming at the Vitals. At 120 yards, the bullet will drop over half a foot, enough to turn a headshot into a body shot or outright miss a shot to an outstretched arm. At 180 yards, the bullet will drop roughly half a yard, enough that a "center of mass" shot will probably hit the pelvis or possibly even a leg, and a shot to the lower leg (to avoid upper leg armor, perhaps) will hit the ground. At 240 yards, the bullet will drop just shy of a full yard, which will turn a torso shot into a leg shot, or a leg shot into a puff of dust on the ground in front of the target. At 300 yards, the bullet will drop by over a yard - a headshot will probably hit the abdomen, and a center of mass shot will hit the ground.

So, yeah, bullet drop is something that needs to be accounted for beyond fairly close range. Granted, a lot of combat tends to be in that short range, but when range is longer a flat trajectory will make it easier to hit what you're aiming at.
It's likely that your sights aren't set for zero range, which pushes out the range at which you can get away with not worrying about it (at the cost of making you shoot a little high at shorter ranges).

Though that would mean that the barrel isn't pointed straight at the target...
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Originally Posted by Varyon View Post
Sadly, gyrocs tend to be too small for HE/HEC to be of much use. Assuming that relationship (120mm mortar being equivalent to 155mm artillery) is fairly constant, 15mm HE gyroc would hold about as much explosive as 18.5mm HE, taking its 2d cr ex [1d-1] to 2d+2 cr ex [1d], which is an improvement, but probably not enough of one to make HE attractive in such a small caliber. HEAT (which I feel should be available at TL9 in 15mm, for 7d(5) imp) and APHEX are much better candidates for gyroc payloads.
Well, the HE is good if you're shooting at targets with next to no DR so it will penetrate. Otherwise, skip it.
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Old 11-19-2019, 08:14 PM   #32
AlexanderHowl
 
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Default Re: Different Gyroc Designs

600 yards/second is a little low for high speed rounds. A 50 BMG (a 12.7mm round) goes over 1,000 yards/second while the 220 Swift (a 5.7mm round) goes over 1,400 yards/second. Faster speeds are known for tank guns and artillery.
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Old 11-20-2019, 05:57 AM   #33
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Default Re: Different Gyroc Designs

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Originally Posted by Varyon View Post
A target 60 yards out will be reached in about 1/10th of a second by a typical (600 yards/second) rifle round. That becomes 1/5 s for 120 yards, 3/10 s for 180 yards, 2/5 s for 240 yards, and finally 1/2 s for 300 yards. At 60 yards, the bullet will drop about 2 inches, which isn't likely to make a difference unless you were aiming at the Vitals. At 120 yards, the bullet will drop over half a foot, enough to turn a headshot into a body shot or outright miss a shot to an outstretched arm. At 180 yards, the bullet will drop roughly half a yard, enough that a "center of mass" shot will probably hit the pelvis or possibly even a leg, and a shot to the lower leg (to avoid upper leg armor, perhaps) will hit the ground. At 240 yards, the bullet will drop just shy of a full yard, which will turn a torso shot into a leg shot, or a leg shot into a puff of dust on the ground in front of the target. At 300 yards, the bullet will drop by over a yard - a headshot will probably hit the abdomen, and a center of mass shot will hit the ground.
Nope. Firstly, while that bullet might average 600 yards/s over it's whole range, it's muzzle velocity is probably more like 900-1000 yards/s.

Secondly, you adjust the sights on your rifle such that the bullet follows a parabolic trajectory and that this trajectory peaks at some known maximum, probably +5 inches for a weapon intended for shooting humans. That means that from 0 yards out to t he point where the bullet has dropped to -5 inches you know that a shot at heart level is going to go into the lungs, heart, or liver, etc.

So, yes it's accounted for, true. But not on the battlefield unless you're trying for head shots past a couple opf hundred metres. And, by the by, outside 200m is longish range for a firefight with small arms, and part 400m is definitely long range (call in some artillery).

Quote:
Sadly, gyrocs tend to be too small for HE/HEC to be of much use. Assuming that relationship (120mm mortar being equivalent to 155mm artillery) is fairly constant, 15mm HE gyroc would hold about as much explosive as 18.5mm HE, taking its 2d cr ex [1d-1] to 2d+2 cr ex [1d], which is an improvement, but probably not enough of one to make HE attractive in such a small caliber. HEAT (which I feel should be available at TL9 in 15mm, for 7d(5) imp) and APHEX are much better candidates for gyroc payloads.
HEAT rounds are notoriously hard to make function well in small diameter warheads, especially long pointy ones. There just isn't room for the liner, explosive, and a good fuse. Gyrocs would fare better than conventional rounds because of the much kinder launch stresses, but even so it's be tricky. Like the small HEMP rounds in UT they should probably have (5) penetration (and unlike them should not be impaling - though those HEMP rounds shouldn't be either, if only for game balance reasons).
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Old 11-20-2019, 11:45 AM   #34
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Default Re: Different Gyroc Designs

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Originally Posted by Varyon View Post
So, yeah, bullet drop is something that needs to be accounted for beyond fairly close range.
It's also rather well known and easily solved even by simple mechanical calculators. The main situation where it actually matters is when you're wrong about the range to the target; if you think the flight time is 0.2s (8" drop) and it's actually 0.3s (18" drop) you just missed by 10".

Note that not knowing the range is also a problem against moving targets, and against fast moving target it's a very large problem. If you're shooting at passengers in a vehicle moving at 30 mph (44'/s), it only takes about a 0.02s error in estimated travel time (corresponding to 10" lateral displacement) to completely miss.
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Old 11-20-2019, 12:33 PM   #35
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Default Re: Different Gyroc Designs

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Originally Posted by AlexanderHowl View Post
600 yards/second is a little low for high speed rounds. A 50 BMG (a 12.7mm round) goes over 1,000 yards/second while the 220 Swift (a 5.7mm round) goes over 1,400 yards/second. Faster speeds are known for tank guns and artillery.
Yeah but AK's or .300 blackout aren't going to be substantially slower and SBRs can get slower yet. Heck look at the .500 Beowulf and similar cartridges like that. it's slow, but not that slow.

There are other issues with faster: the higher the velocity the more propellant (or the more energetic/hotter your propellant needs to be unless you can somehow emulate a light gas gun) and that can mean more recoil/heavier and larger round and/or wearing out your barrel and increased heating. .220 Swift has a case nearly as large as 7.62 NATO for example. Tank guns have a propellant charge as heavy as the projectile itself and that cuts down EFC life by several times easily compared to HE/HE-Frag. There also seems to be some actual difference performance/efficiency wise when it comes to velocity and propellant (propellant for 5.56 NATO is like 35-40% of total recoil impulse, whereas with 7.62 mm - both kinds - it can be closer to 25%)

I also think the .220 swift is only going to get the velocities you claim if you use a lighter bullet (2.5-3 grams I think, vs 5.56 NATO's 4 grams for M855A1. Heck the old M262 was heavier despite a lower velocity and the US military I've read tested 5.56mm rounds as heavy as 100 grains.) light but fast bullets have drawbacks over slower but heavier in terms of external (and in some cases, terminal) ballistics.

More velocity means more recoil, and that means a heavier rifle or a more complex rifle (recoil mitigation, which has alot of issues tied to it, like a Muzzle brake) or it means a lighter round (which can also have drawbacks.) Odd as it sounds, speed can be useful, but it isn't everything when it comes to firearms. Or tank guns. The US 120mm APFSDS actually went with a somewhat slower round (~1550 m/s vs ~1740 m/s with certain rounds I believe) than its european counterparts because they wanted a heavier round. Which for a given aspect ratio means a thicker (more rigid) penetrator but may also mean more length (which increases penetration in a monolithic KEP)
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Old 11-20-2019, 12:58 PM   #36
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Default Re: Different Gyroc Designs

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Originally Posted by Jack Sawyer View Post
More velocity means more recoil
More velocity is generally less recoil at the same energy levels (it's less bullet momentum, though inferior efficiency usually results in somewhat more from gas).
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Old 11-20-2019, 02:04 PM   #37
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Default Re: Different Gyroc Designs

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Originally Posted by Rupert View Post
Nope. Firstly, while that bullet might average 600 yards/s over it's whole range, it's muzzle velocity is probably more like 900-1000 yards/s.

Secondly, you adjust the sights on your rifle such that the bullet follows a parabolic trajectory and that this trajectory peaks at some known maximum, probably +5 inches for a weapon intended for shooting humans. That means that from 0 yards out to t he point where the bullet has dropped to -5 inches you know that a shot at heart level is going to go into the lungs, heart, or liver, etc.

So, yes it's accounted for, true. But not on the battlefield unless you're trying for head shots past a couple opf hundred metres. And, by the by, outside 200m is longish range for a firefight with small arms, and part 400m is definitely long range (call in some artillery).
If bullet drop is such a minor factor, rangefinders (or other methods of knowing exact range) shouldn't give such a massive bonus (+3), at least against targets without significant lateral velocity. If the rangefinder bonus is appropriate, the straight flight of a gyroc should be useful. Of course, having sights mounted parallel to the path of the bullet (rather than intersecting it at some range, as with conventional firearms) does mean you'll always hit a bit below your point of aim, but only by the difference between the location of the sights and the location of the chamber; if you want to hit someone in the eye, aim at their eyebrow.

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Originally Posted by Rupert View Post
HEAT rounds are notoriously hard to make function well in small diameter warheads, especially long pointy ones. There just isn't room for the liner, explosive, and a good fuse. Gyrocs would fare better than conventional rounds because of the much kinder launch stresses, but even so it's be tricky. Like the small HEMP rounds in UT they should probably have (5) penetration (and unlike them should not be impaling - though those HEMP rounds shouldn't be either, if only for game balance reasons).
Yeah, the suggested stats I listed - 7d(5) imp inc (although I left out the inc) - are based on the UT stats, at -1/die on account of being TL9 rather than TL10. The smallest HEAT round I'm aware of is 18.5mm, which according to High Tech became available around 2004, albeit as an experimental round. Its performance left much to be desired (HT puts its stats at 1d(10) cr ex inc; -2/die to drop 2 TL's would put 18.5mm at 5d(5) imp inc, 2.5x as much penetration, based on the UT stats), but considering UT assumes 10mm HEAT as doable at TL10, I assume 15mm should be doable at TL9. It may not be, or may have lackluster performance like the experimental shotgun round, which would mean gyrocs would likely need to rely on APHEX or payloads that don't do direct damage (gases against living targets who lack Sealed, EMP's against unhardened electronics, expendable jammers against drones, etc).

I do agree that imp probably isn't appropriate.

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Originally Posted by Anthony View Post
It's also rather well known and easily solved even by simple mechanical calculators. The main situation where it actually matters is when you're wrong about the range to the target; if you think the flight time is 0.2s (8" drop) and it's actually 0.3s (18" drop) you just missed by 10".

Note that not knowing the range is also a problem against moving targets, and against fast moving target it's a very large problem. If you're shooting at passengers in a vehicle moving at 30 mph (44'/s), it only takes about a 0.02s error in estimated travel time (corresponding to 10" lateral displacement) to completely miss.
Hmmm... I wonder if a gyroc designed to continue tracking in the same direction as the weapon that fired it would be markedly cheaper than a guided/homing one. So, if you need to rotate your to the left aim by 1 degree per second to track a moving target, and you fire while doing so, the gyroc will continue to track to the left at 1 degree per second; so long as the target maintains its current velocity, the gyroc should hit where you were aiming when you pulled the trigger. Could be worthwhile if it's cheaper (and/or more reliable in a target-rich environment).
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Old 11-20-2019, 03:06 PM   #38
Anthony
 
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Default Re: Different Gyroc Designs

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Hmmm... I wonder if a gyroc designed to continue tracking in the same direction as the weapon that fired it would be markedly cheaper than a guided/homing one.
That is a guided missile, you're just using the weapon's sights as your guide. As for practicality, the information is hard to communicate to the missile unless you use a laser to illuminate the target, in which case that's a laser guided missile.
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Old 11-20-2019, 03:27 PM   #39
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Default Re: Different Gyroc Designs

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That is a guided missile, you're just using the weapon's sights as your guide. As for practicality, the information is hard to communicate to the missile unless you use a laser to illuminate the target, in which case that's a laser guided missile.
My suggestion isn't a case where the shooter is keeping the target in his sights as the gyroc is going downrange to hit it (which would indeed by GURPS Guided). Rather, it's a case where the weapon is keeping track of the way the shooter is moving it, and sends that information to the gyroc upon firing. The order of operations is:
  1. Shooter acquires target, determines where he wants to hit it, and aims there.
    (Optional) Shooter flicks the "track my movement" switch.
  2. Shooter tracks the target, keeping his aimpoint where he wants the gyroc to impact.
  3. Shooter pulls trigger. The weapon's internal computer calculates he consistently moved 1 degree to the left prior to shooting.
  4. Weapon sends this information to the igniting gyroc, telling it to arc 1 degree to the left during flight.
  5. Gyroc exits barrel and arcs as per the weapon's instructions. There is no further communication between gyroc and weapon. Provided the shooter was tracking the target properly and it maintains its current velocity, the gyroc will strike where the shooter was aiming, minus any user error (or inherent imprecision of the round).
  6. As soon as the gyroc has exited the barrel, the shooter is free to change position or engage a new target.

It seems like it would mostly be additional cost to the weapon itself, with the gyroc only being marginally more expensive (it can communicate with the weapon it's within, and can adjust its angle of flight, but doesn't need the constant communication of a Guided round, or the ability to acquire and track the target of a Homing round). Of course, it may be that the situations in which this feature would be useful are too hectic for the shooter to actually make use of it.
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Old 11-20-2019, 03:42 PM   #40
Anthony
 
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Default Re: Different Gyroc Designs

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Originally Posted by Varyon View Post
My suggestion isn't a case where the shooter is keeping the target in his sights as the gyroc is going downrange to hit it (which would indeed by GURPS Guided). Rather, it's a case where the weapon is keeping track of the way the shooter is moving it, and sends that information to the gyroc upon firing.
Oh, you want it to recognize the movement of the weapon before firing? I guess that's probably technically possible (it's essentially a form of coordinate guiding) but it doesn't seem at all easy, because the bullet has to know its own position with sufficient accuracy.
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