Figured out a way to have "effective range" in GURPS; still need numbers

[Everett]

One things that's bugged me for a while is that the Acc difference between, say, handguns, SMG's and rifles doesn't result in enough of a difference in what your odds of hitting a target at range are. Of course, the magnitude of Acc numbers in general are right (much better than in 2e), it's that the difference isn't enough, and it seems that pistols and SMG's stand almost as good a chance of hitting at long range if you aim as rifles do, and not aiming there's no difference at all. For an example, a 9mm round has (IIRC) a muzzle velocity of generally around 900 fps; at 100 yards, that's a full third of a second to reach the target.

Basically, the idea is to give an "effective range" based on the skill the weapon uses, with Guns (rifle) subdivided into "Assault rifles and Carbines" (anything using Guns (rifle) that does has 5 dice of damage or less (just the number, which I suppose means 5d+2 or less, carbines fall into this range too by definition), and "Battle Rifles" that do 6d-1 damage or more. (Chosen partly to include everything generally considered a battle rifle) Guns (pistol) would have it's own figure used for all of them, Guns (SMG) would be a little more, Guns (LMG) would be the same as battle rifles. Gunner skill would probably be about 25-50% more than for LMG's (assuming that using Gunner essentially means using a tripod by default.) Weapons with a scope fitted ignore these rules. For guns that are Fine or Very Fine (accurate), you don't get a higher effective range, but you still get the higher Acc bonus if you Aim.

What the effective range actually does is not a limit, rather, past that each increment beyond that on the speed/range table is simply -2 rather than -1. (NOT doubling the total range penalty.) So a high skill character can still fire at the targets farther away, just less likely to hit, and an average character still hits some of the time, just not that often.

For example, if the effective range for Guns (pistol) is 30 yards (see below), a character shooting at a target 60 yards away would have a range penalty of -11 (-7 for up to 30 yards, than -2 for both the 50 and 70 yard entries on the table)

My current problem is that the actual "Effective Ranges" I'm not particularly sure of. Battle rifles and LMG'S were traditionally considered good to around 300 yards in actual combat experience, if I remember correctly. For Guns (pistol) - ? I'm assuming 30 yards is a good figure past which range penalties get increasingly severe. For Assault Rifles and SMG'S I don't really have much of an idea. I would assume SMG's would have an effective range longer than pistols, but not that much; 50 yards maybe? (But that's only one line on the speed/range table?) 75 yards seems a bit long. Again, you can still hit things farther than that, just higher range penalties. For Assault Rifles (and carbines), I would make a wild guess of maybe 150? yards, but don't have much real idea.

Anyone able to provide some insight?







(Pre-20th century smoothbores of all types have an effective range of 0; in other words just double all range penalties. (To those who have seen people reliably hitting targets at range today with muskets, I would ask whether it was built to 18th century tolerances (blacksmithing, not machining), and used a bullet that was not truly round (as with most 18th century musket balls.) (18th century rifles were use "modern" rules, they were accurate enough.))

(For cannon, pre-industrial or not, tank and antitank guns and artillery in direct file, I would consider the GUPRS system not particularly suited to modeling that type of combat.)

[Rupert]

Originally Posted by Everett

One things that's bugged me for a while is that the Acc difference between, say, handguns, SMG's and rifles doesn't result in enough of a difference in what your odds of hitting a target at range are. Of course, the magnitude of Acc numbers in general are right (much better than in 2e), it's that the difference isn't enough, and it seems that pistols and SMG's stand almost as good a chance of hitting at long range if you aim as rifles do, and not aiming there's no difference at all. For an example, a 9mm round has (IIRC) a muzzle velocity of generally around 900 fps; at 100 yards, that's a full third of a second to reach the target.

It's more like 1200 ft/s.

My current problem is that the actual "Effective Ranges" I'm not particularly sure of. Battle rifles and LMG'S were traditionally considered good to around 300 yards in actual combat experience, if I remember correctly. For Guns (pistol) - ? I'm assuming 30 yards is a good figure past which range penalties get increasingly severe. For Assault Rifles and SMG'S I don't really have much of an idea. I would assume SMG's would have an effective range longer than pistols, but not that much; 50 yards maybe? (But that's only one line on the speed/range table?) 75 yards seems a bit long. Again, you can still hit things farther than that, just higher range penalties. For Assault Rifles (and carbines), I would make a wild guess of maybe 150? yards, but don't have much real idea.

Anyone able to provide some insight?

20th century battle rifles were, when aimed, useful out to 6-800 yards, more if volley fired. 300 yards/metres is the effective range of a modern assault rifle, give or take.

Now, here's the thing - unaimed, as in not aimed even a little bit, is more 'wild shot' territory. Aimed a bit, but not taking time to do so properly (i.e. a normal attack), any modern longarm with reasonable ergonomics has about the same effective range, and pistols have their own which is also pretty much the same for all of them. That range should be given as a combination of range and size penalties, if you're going to do this.

In no case should this rule apply to properly aimed (i.e. time taken, +Acc bonus acquired) shots, because Acc already takes into account handgun vs longarm, good vs bad sights, poor ballistics, etc. Also, when aimed there's a huge difference between the 'effective' range of a handgun and a rifle. Most modern pistols have Acc 2, some have Acc 1. SMGs have 3-4, and rifles 4-5. This an SMG is about +2 Acc over a pistol, and a rifle is about +3 Acc. Because of how the range/speed table works, this means a SMG has about twice the effective range of a pistol, and a rifle has about three times the effective range of a pistol. To look at it another way, at the range you have a given chance to hit a person standing in the open with a pistol, a rifle gives you the same chance to shoot them in the vitals. Either way, it's a huge increase in accuracy and range.

[RyanW]

Mathematically the same to worry instead about the range modifier at effective range. If actual range modifier is higher, add the difference on top.

Not sure I think such a rule is necessary, but this way doesn't require figuring how many range steps are and aren't doubled.

[Varyon]

Originally Posted by Everett

(Pre-20th century smoothbores of all types have an effective range of 0; in other words just double all range penalties. (To those who have seen people reliably hitting targets at range today with muskets, I would ask whether it was built to 18th century tolerances (blacksmithing, not machining), and used a bullet that was not truly round (as with most 18th century musket balls.) (18th century rifles were use "modern" rules, they were accurate enough.))

Ahem. Based on the Master's thesis linked in there, an "effective range" of 70 yards seems appropriate, at least at mid-late TL 4 (specifically, the English Civil War). It's been a while since I read it, but IIRC the results seen from the testing were consistent with contemporary military documents.


Outside of muskets (which have different ballistics from modern bullets*), I think basing effective range off muzzle velocity (optionally with 1/2D range coming into play**) would be most appropriate. You're basically looking at how low it takes the bullet to reach the target, and how likely it is the target will have moved unpredictably in the time between firing and the bullet reaching. ~1/3 second probably isn't a terrible value to use here. Now, muzzle velocities are often given in feet per second (fps), so a simple method is to simply take the muzzle velocity in fps and divide by 10 to get effective range in yards (divide by 3 to change feet to yards, divide by 3 for 1/3 second, round the divisor up for ease of math). If you feel a different amount of time is more appropriate, feel free to adjust the divisor as appropriate (1/5 second would use a divisor of 15, for example).

*The weapon used in the Master's thesis averaged around a 400 fps muzzle velocity, which would give it an effective range of 40 yards, which we'll round up to 50. Optionally, you'd be looking at an additional -1 per range increment beyond 50 yards when firing at a target moving unpredictably, and an additional -1 per range increment beyond 70 yards at any target (due to musket ballistics); an unpredictably-moving target at 100 yards would thus be at -13 (-10 for range, -2 for two steps above 50, -1 for 1 step above 70). Of course, the two are close enough it might not be bad to choose one for the effective range, with a note that it's actually an additional -2 per step above effective range, making the above either -12 (if using 70 yards) or -14 (if using 50 yards).

**Realistically, bullets slow down after they leave the muzzle due to air resistance. This is where the 1/2D range comes from. If you don't mind some more complication, assume the bullet is going at 1/2 muzzle velocity at the 1/2D range (damage scales roughly with the square root of kinetic energy, which makes it linear with velocity) and that the drop in velocity is constant from range 0 to 1/2D (it's not linear, otherwise Max would simply be twice the 1/2D, but using the average isn't horrible). Just throwing some numbers out, if you have a weapon that has muzzle velocity of 1200 fps and 1/2D of 100 yards, that means it's going at a speed rate of 1200 fps at 0 yards and 600 fps at 100 yards, for an average of 900 fps over this range; that gives it an effective range of 90 yards, which we'll round up to 100 (in this case, effective range = 1/2D, but that won't always be the case).


EDIT: Also, please note that, while a mere +2 or +3 to Acc doesn't sound like much, for a given skill level that's effectively x2 or x3 to range. For example, if you feel a 50% hit chance (effective skill 10) is appropriate for determining effective range, then for a skill-12 shootist Aiming for 3 seconds (for Acc+2), an Acc 2 weapon has an effective range of 20 yards, an Acc 4 weapon has an effective range of 50 yards, and an Acc 5 weapon has an effective range of 70 yards. Higher skill or a lower acceptable hit chance will, of course, increase these ranges.

[Everett]

Originally Posted by RyanW

Mathematically the same to worry instead about the range modifier at effective range. If actual range modifier is higher, add the difference on top.

Not sure I think such a rule is necessary, but this way doesn't require figuring how many range steps are and aren't doubled.

Took me a while to figure out what you meant, but that's much better way to handle it.

Originally Posted by Rupert

20th century battle rifles were, when aimed, useful out to 6-800 yards, more if volley fired. 300 yards/metres is the effective range of a modern assault rifle, give or take.

Ah, OK then, remembered it wrong. In WWII militaries found out they had 600-800 yards from rifles when they only really needed 300; I misremembered 300 yards as the first figure.

Originally Posted by Varyon

Ahem. Based on the Master's thesis linked in there, an "effective range" of 70 yards seems appropriate, at least at mid-late TL 4 (specifically, the English Civil War). It's been a while since I read it, but IIRC the results seen from the testing were consistent with contemporary military documents..

Giving an "effective range" of 0 wasn't actually meant as an actual effective range; it was instead a convenient way of "double range penalties for smoothbore muskets" that fit well in with the rule idea. I thought it was cleaner than "double range penalties for muskets" as a separate rule.

What's your take on "muskets take double range penalties" as a standalone rule? (Their Acc would still be the same as RAW.)

Originally Posted by Varyon

[Outside of muskets (which have different ballistics from modern bullets*), I think basing effective range off muzzle velocity (optionally with 1/2D range coming into play**) would be most appropriate. You're basically looking at how low it takes the bullet to reach the target, and how likely it is the target will have moved unpredictably in the time between firing and the bullet reaching. ~1/3 second probably isn't a terrible value to use here. Now, muzzle velocities are often given in feet per second (fps), so a simple method is to simply take the muzzle velocity in fps and divide by 10 to get effective range in yards (divide by 3 to change feet to yards, divide by 3 for 1/3 second, round the divisor up for ease of math). If you feel a different amount of time is more appropriate, feel free to adjust the divisor as appropriate (1/5 second would use a divisor of 15, for example).

A pretty good idea. I actually almost gave an effective range based on damage dice, as a proxy for muzzle velocity, and didn't want to get bogged down in various pistol rounds, since I figured that the difference as a practical matter wouldn't be enough to show up on the speed/range table.

The problem is that it gives a 9mm around 120 yards, and battle rifles around 250-300 yards, which while mathematically correct isn't really around the right numbers for the intention.

Originally Posted by Rupert

In no case should this rule apply to properly aimed (i.e. time taken, +Acc bonus acquired) shots, because Acc already takes into account handgun vs longarm, good vs bad sights, poor ballistics, etc. Also, when aimed there's a huge difference between the 'effective' range of a handgun and a rifle. Most modern pistols have Acc 2, some have Acc 1. SMGs have 3-4, and rifles 4-5. This an SMG is about +2 Acc over a pistol, and a rifle is about +3 Acc. Because of how the range/speed table works, this means a SMG has about twice the effective range of a pistol, and a rifle has about three times the effective range of a pistol. To look at it another way, at the range you have a given chance to hit a person standing in the open with a pistol, a rifle gives you the same chance to shoot them in the vitals. Either way, it's a huge increase in accuracy and range.

Originally Posted by Varyon

[
EDIT: Also, please note that, while a mere +2 or +3 to Acc doesn't sound like much, for a given skill level that's effectively x2 or x3 to range. For example, if you feel a 50% hit chance (effective skill 10) is appropriate for determining effective range, then for a skill-12 shootist Aiming for 3 seconds (for Acc+2), an Acc 2 weapon has an effective range of 20 yards, an Acc 4 weapon has an effective range of 50 yards, and an Acc 5 weapon has an effective range of 70 yards. Higher skill or a lower acceptable hit chance will, of course, increase these ranges.

It seems that I did underestimate how much of a difference a point of Acc makes. You've got a point, but it seems that giving a battle rifle an Acc of more like 6 makes more sense in that context. (And an assault rifle an Acc of 5.) Probably giving rifles of all kinds +1 Acc would be a far better idea than what I proposed; it would give the SMG twice the range of the pistol, and the (battle) rifle four times the range of the pistol, and more importantly twice the range of the SMG.

Part of the problem revolves around various weapons in a universe of mine. There's a SMG that's based off of the Finnish KP/31, but in .455 caliber; since the KP/31 is essentially +1 Acc compared to other 9mm SMG's, that would imply giving it the same Acc (5) as the battle rifle (based off the M14), while both of them would have the same bulk. (Which doesn't make all that much sense to me, but on the other hand +3 from RoF makes up for that, which is probably about right.) Any advice on the problem? Just drop the SMG back down to a "standard" Acc 4?

[Kallatari]

I just want to start by saying I am not a guns expert and have no insight into what their "effective ranges" are, other than I understand its concept. But I'm happy to throw in some additional rule ideas and brainstorm...

First, I just wanted to say that I think conceptually it's a good idea. I understand that something works reliably to a certain range, then after that it gets much harder to hit something. (Not sure I'd use such a rule, but I get it).

But I'm not sure if adding yet another stat (the "effective range") to a weapon is handy. Can you modify it independently? Will there be new gun modifier traits like Fine (Effective Range)? Do modifiers to bullet range from the type of bullet, firearm, etc., also modify effective range? And thus do we have to go to every existing gun and bullet modifier to see what it's impact on effective range would be and add rules there as well. I'm not saying don't do it, just that there are a lot of dots to connect.

What if instead, you use an existing stat, such as Acc. No rule tweaks would be need, so anything that affects Acc affects your "effective range." The rule itself could be, say, up to a range penalty of the weapon's Acc, you use the normal -1 per range increment penalty, and everything beyond that is doubled to -2 per range increment. So if a rifle is Acc 5, then up to the first -5 penalty from range give you up to -5 to hit, but for -6 and beyond, you double the difference, so -6 becomes -7, -7 becomes -9, -8 becomes -11, etc.

An even easier method to game (less math) - but possibly providing too much benefit at short range - would be to double ALL range penalties, but then you can automatically reduce the range penalty by the Gun's Acc, whether aimed or not; this can never result in a bonus to hit. This effect is cumulative with the bonus to hit from Acc for aiming an attack.

If the ranges obtained by this method where the penalty doubles aren't reasonable for matching a real "effective range", then maybe double them; e .g., an Acc 5 gun assault rifle gives you the normal penalty up to -10, then doubles afterwards, while an Acc 2 pistol gives you the normal penalty up to -4 (or -6?), then doubles afterwards. Or triple it?

I have no clue if that gives reasonable effective ranges between the different types of guns (i.e., pistol vs SMG vs assault rifle), so maybe this is not what you are looking for. Of hand, the double Acc seems about right for the rifles, but too short for pistols... but again, I'm not an expert at this. This was just brainstorming a possible way to do what you wanted using an existing stat... which admittedly might not be the best way to do it.


As a side question, would you apply a similar rule for thrown weapons? bows? beam weapons?

[Everett]

Originally Posted by Kallatari

I just want to start by saying I am not a guns expert and have no insight into what their "effective ranges" are, other than I understand its concept. But I'm happy to throw in some additional rule ideas and brainstorm...

First, I just wanted to say that I think conceptually it's a good idea. I understand that something works reliably to a certain range, then after that it gets much harder to hit something. (Not sure I'd use such a rule, but I get it).

But I'm not sure if adding yet another stat (the "effective range") to a weapon is handy. Can you modify it independently? Will there be new gun modifier traits like Fine (Effective Range)? Do modifiers to bullet range from the type of bullet, firearm, etc., also modify effective range?
And thus do we have to go to every existing gun and bullet modifier to see what it's impact on effective range would be and add rules there as well. I'm not saying don't do it, just that there are a lot of dots to connect.

Honestly, that's what I wanted to avoid by not giving each gun its own stat. I was planning to use a blanket number for "everything that uses Guns(pistol)," "Everything that uses Guns(SMG)," "Everything that uses Guns(rifle) and does 5d+2 or less damage" (which translates to assault rifles and carbines), and "Everything that uses Guns(rifle) and does 6d-1 or more damage, (battle rifles), as well as everything that uses Guns(LMG)" Changing ammo type or anything else doesn't change anything. It's a rule, not a stat. I'm currently (was) leaning toward not having Fine (Accurate) change it either.

After the discussion here though, I didn't realize how much 1-2 points of Acc actually changes range. I'm now leaning simply toward giving all rifles +1 Acc instead.

Originally Posted by Kallatari

As a side question, would you apply a similar rule for thrown weapons? bows? beam weapons?

Thrown weapons have such short maximum ranges that it doesn't really matter. For bows, honestly, even the most realistic rules in GURPS "politely ignore" that time of flight at long ranges is so long that target probably won't even be in the same hex as when you fired. Long range fire with bows would only really be useful IRL as massed fire from a large number of archers against massed targets. Perfectly fine for battlefield use, and able to hit a static target, but in a character scale fight completely useless at long range.

[weby]

Basically GURPS range system works fairly well for things like quick pistol shots, but fail rather badly even with all the fixes from places like tactical shooting.

One of the problems is the thing that you likely have noticed where at the extreme ranges for a weapon the probability of hit drops much faster than GURPS rules indicate.

As example, in conditions where I get about 50% hit chance at 1000 meters(effective skill 10), according to GURPS I am then supposed to have 37% chance at 1500 meters and and 26% at 2000 meters.. whereas in reality is is more like "1500, yeah, I might at some point hit it, and 2000, no way ever..

The -2/step might really not be enough to give proper reduction at that point, but seems better than -1.


But then there is also the problem where current ACC 4 carbines are more accurate than WW I acc 5 rifles. In fact I guess if a new AR-15 style rifle would shoot as inaccurately as a even a typical WW 2 sniper rifle, I would return it as defective. Basically if you shoot a 4 MOA rifle(a typical WW2 rifle in good condition) at 1000 meters, just the mechanical accuracy would limit you to about 1 meter groups, whereas more current normal rifles would mechanically shoot maybe 30cm groups without being exceptionally accurate. Of course the shooter skill and ammo quality the added to the mix and it gets really complicated fast.

But that rant aside:
I have been tempted to totally rework the rifle shot mechanics in my games, but have not really found a good way to model them without being too arbitrary.