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Old 09-05-2013, 04:05 PM   #1
Varyon
 
Join Date: Jun 2013
Default GURPS Overhaul - Rate of Fire

I've debated posting this, as I believe Anthony's houserule in the RoF thread is a good deal more gameable, but ultimately decided not to have all my work go to waste. To design this system, I made (in Photoshop) circles of various SM's (between -10 and 1) and overlapped them. I assumed that hitting an SM "on the number" (MoS 0) meant centering the "hit sphere" exactly between its perimeter and the perimeter of the next smallest SM. I also made the assumption that distribution of bullets within the hit sphere was completely random, meaning how close the targeted area was to the center of the sphere made no difference. I believe this is indeed the case with shotguns, but may not be true of other weapons. Please note that if you use this variant, you should probably use a semi-cumulative wounding system, rather than GURPS default, as otherwise this will make high RoF weapons far too lethal.

This system replaces the existing RoF rules. First off, high RoF does not (directly) give a bonus to the chance to hit. Also, weapons no longer have a Rcl statistic, rather they have Spread, which is a negative number. The more negative the number, the less spread the weapon suffers when firing at maximum RoF. Unchoked shotguns firing shot have Spread -1 (one inch spread per yard of range, or 1/36 radians), while a mounted machine gun may have Spread -12 (one inch spread per ~28 yards of range, or 1/1000 radians).

Spread represents the maximum Size + Range penalty the weapon can suffer before it becomes possible to hit with a fraction of the shots fired (rather than all-or-nothing) [i]assuming the weapon stays on-target[i] (see later). Speed does not factor into this calculation (but note you still are penalized as normal for it). For an unchoked shotgun, this would be when firing at an SM+0 target at 3 yards, while for a mounted machine gun you're looking at shooting an SM +0 target at 200 yards. For high-spread weapons, it may be more appropriate to use the distance from the muzzle to the target (in the case of a typical shotgun, I think this adds around 1 yard to this distance), rather than from the user to the target.

At penalties beyond Spread, use the following table to determine what fraction of the rounds fired actually hits. I assume here that spread follows a completely random pattern within the sphere - that is, a bullet is as likely to hit a given area as any other area the same size (provided both areas are fully within the spread "sphere"), regardless of how close to the center of the spread these areas are.

Code:
	-3	-2	-1	0	1	2	3	4	5	6	7
0	0	0	0	1	1	1	1	1	1	1	1
-1	0	0	0	0.95	1	1	1	1	1	1	1
-2	0	0	0.05	0.95	1	1	1	1	1	1	1
-3	0	0	0.05	0.8	1	1	1	1	1	1	1
-4	0	0	0.15	0.65	1	1	1	1	1	1	1
-5	0	0	0.25	0.65	0.95	1	1	1	1	1	1
-6	0	0	0.2	0.45	0.65	0.75	0.8	0.85	0.9	0.95	1
-7	0	0.05	0.25	0.35	0.45	0.45	0.45	0.45	0.45	0.45	0.45
-8	0	0.15	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25
-9	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.1
The numbers across the top are Margin of Success (note MoS -1 is the same as MoF 1), while the numbers down the left side are for the Range+Size penalty relative to Spread (so shooting at SM+1 target at 30 yards is a -6 total penalty, so if using an unchoked shotgun - Spread -1 - you would use the line corresponding to -5). For penalites beyond Spread-9, each additional -1 increases the MoF range by 1 and halves the number of hits (so at Spread-10 you can have MoF 4 and still hit, but will only hit with 5% of the shots; at Spread-15, you can go down to MoF 9 but will only hit with 0.1563%). For ease of use, don't assess any range penalty beyond Spread-9 (you're essentially getting +1 per -1) and follow a 1-2-5-10 pattern (so our Spread-15 example would hit instead with 0.1%).


Of course, GURPS RoF is given in shots per second, and the initial roll just tells you where you start - keeping on-target for an entire second isn't exactly easy. Make a Per-based weapon or Observation roll at -10, plus any penalty due to speed (but not range). Sighted shooting applies the weapon's Acc or +4 (whichever is larger) to the roll. Having all rounds with clearly-visible impacts (explosive rounds, or incendiary rounds in low light) or using a tracer mix grants +2, while having both or using all tracers grants +4 (using all explosive tracer rounds has no additional effect). Add you MoS (or MoF) to your initial MoS to determine how close you are to the target at the end. The actual percentage of rounds that will hit is going to be an average of all points from start to finish. For example, let's say you're firing a mounted machine gun (Spread -12) at an SM+1 vehicle that is 500 yards away and traveling at Move 30. 500 yards is -14, so with SM+1 we're at -1 from Spread. Let's say we roll well enough for MoS 3. Now we need to stay on-target with our Per-based roll, working against a penalty of -17 (-10 base, -7 speed). Let's say we end up with MoF 5. We add this to our previous result, for a total MoF 2. Now we need to average all our hits together to determine the actual hit pecentage. MoS 3 is 100%, as are MoS 2 and 1. MoS 0 is 95%, and MoF 1 and 2 are each 0%. 3.95/5=.79, for 79% hits. Were we firing at RoF 30, we'd be looking at 23 or 24 hits (average is 23.7).


The big problems with this system are the need for multiple rolls, the need to calculate average number of hits, and, most importantly, a lack of Spread values for weapons - seriously, shotguns I got from Tactical Shooting, mounted machine guns from a mention in the other thread, and I have no clue about the spreads of other weapons (other than that they probably have Spread between these two).

Next up, an option to randomize number of hits!
Varyon is offline   Reply With Quote
Old 09-05-2013, 04:07 PM   #2
Varyon
 
Join Date: Jun 2013
Default Re: GURPS Overhaul - Rate of Fire

Thanks to the word count limit, I'll only post a few of the tables here. If anyone wants others (I have made them for RoF 2 - 100), feel free to PM me. To use the table, find your RoF and your percentage value (from above) and roll d% (this is 2 d10's, with one marking the tenth's place and one the hundredth's place; .00 is 1.00). The number in the column is your target. For example, with RoF 20 and 45% hits, 1.00 or lower gets you 3 hits, .98 or lower gets you 4, .87 gets you 7, .41 gets you 10, and .01 gets you 15.

RoF 2
Code:
		1	2
	0.95	1.00	0.90
	0.9	0.99	0.81
	0.85	0.98	0.72
	0.8	0.96	0.64
	0.75	0.94	0.56
	0.7	0.91	0.49
	0.65	0.88	0.42
	0.6	0.84	0.36
	0.55	0.80	0.30
	0.5	0.75	0.25
	0.45	0.70	0.20
	0.4	0.64	0.16
	0.35	0.58	0.12
	0.3	0.51	0.09
	0.25	0.44	0.06
	0.2	0.36	0.04
	0.15	0.28	0.02
	0.1	0.19	0.01
	0.05	0.10	0.00
RoF 3
Code:
		1	2	3
	0.95	1.00	0.99	0.86
	0.9	1.00	0.97	0.73
	0.85	1.00	0.94	0.61
	0.8	0.99	0.90	0.51
	0.75	0.98	0.84	0.42
	0.7	0.97	0.78	0.34
	0.65	0.96	0.72	0.27
	0.6	0.94	0.65	0.22
	0.55	0.91	0.57	0.17
	0.5	0.88	0.50	0.13
	0.45	0.83	0.43	0.09
	0.4	0.78	0.35	0.06
	0.35	0.73	0.28	0.04
	0.3	0.66	0.22	0.03
	0.25	0.58	0.16	0.02
	0.2	0.49	0.10	0.01
	0.15	0.39	0.06	0.00
	0.1	0.27	0.03	0.00
	0.05	0.14	0.01	0.00
RoF 5
Code:
		1	2	3	5
	0.95	1.00	1.00	1.00	0.77
	0.9	1.00	1.00	0.99	0.59
	0.85	1.00	1.00	0.97	0.44
	0.8	1.00	0.99	0.94	0.33
	0.75	1.00	0.98	0.90	0.24
	0.7	1.00	0.97	0.84	0.17
	0.65	0.99	0.95	0.76	0.12
	0.6	0.99	0.91	0.68	0.08
	0.55	0.98	0.87	0.59	0.05
	0.5	0.97	0.81	0.50	0.03
	0.45	0.95	0.74	0.41	0.02
	0.4	0.92	0.66	0.32	0.01
	0.35	0.88	0.57	0.24	0.01
	0.3	0.83	0.47	0.16	0.00
	0.25	0.76	0.37	0.10	0.00
	0.2	0.67	0.26	0.06	0.00
	0.15	0.56	0.16	0.03	0.00
	0.1	0.41	0.08	0.01	0.00
	0.05	0.23	0.02	0.00	0.00
RoF 7
Code:
		1	2	3	5	7
	0.95	1.00	1.00	1.00	1.00	0.70
	0.9	1.00	1.00	1.00	0.97	0.48
	0.85	1.00	1.00	1.00	0.93	0.32
	0.8	1.00	1.00	1.00	0.85	0.21
	0.75	1.00	1.00	0.99	0.76	0.13
	0.7	1.00	1.00	0.97	0.65	0.08
	0.65	1.00	0.99	0.94	0.53	0.05
	0.6	1.00	0.98	0.90	0.42	0.03
	0.55	1.00	0.96	0.85	0.32	0.02
	0.5	0.99	0.94	0.77	0.23	0.01
	0.45	0.98	0.90	0.68	0.15	0.00
	0.4	0.97	0.84	0.58	0.10	0.00
	0.35	0.95	0.77	0.47	0.06	0.00
	0.3	0.92	0.67	0.35	0.03	0.00
	0.25	0.87	0.56	0.24	0.01	0.00
	0.2	0.79	0.42	0.15	0.00	0.00
	0.15	0.68	0.28	0.07	0.00	0.00
	0.1	0.52	0.15	0.03	0.00	0.00
	0.05	0.30	0.04	0.00	0.00	0.00
RoF 9
Code:
		1	2	3	5	7	9
9.00	0.95	1.00	1.00	1.00	1.00	0.99	0.63
	0.9	1.00	1.00	1.00	1.00	0.95	0.39
	0.85	1.00	1.00	1.00	0.99	0.86	0.23
	0.8	1.00	1.00	1.00	0.98	0.74	0.13
	0.75	1.00	1.00	1.00	0.95	0.60	0.08
	0.7	1.00	1.00	1.00	0.90	0.46	0.04
	0.65	1.00	1.00	0.99	0.83	0.34	0.02
	0.6	1.00	1.00	0.97	0.73	0.23	0.01
	0.55	1.00	0.99	0.95	0.62	0.15	0.00
	0.5	1.00	0.98	0.91	0.50	0.09	0.00
	0.45	1.00	0.96	0.85	0.38	0.05	0.00
	0.4	0.99	0.93	0.77	0.27	0.03	0.00
	0.35	0.98	0.88	0.66	0.17	0.01	0.00
	0.3	0.96	0.80	0.54	0.10	0.00	0.00
	0.25	0.92	0.70	0.40	0.05	0.00	0.00
	0.2	0.87	0.56	0.26	0.02	0.00	0.00
	0.15	0.77	0.40	0.14	0.01	0.00	0.00
	0.1	0.61	0.23	0.05	0.00	0.00	0.00
	0.05	0.37	0.07	0.01	0.00	0.00	0.00
RoF 10
Code:
		1	2	3	5	7	10
	0.95	1.00	1.00	1.00	1.00	1.00	0.60
	0.9	1.00	1.00	1.00	1.00	0.99	0.35
	0.85	1.00	1.00	1.00	1.00	0.95	0.20
	0.8	1.00	1.00	1.00	0.99	0.88	0.11
	0.75	1.00	1.00	1.00	0.98	0.78	0.06
	0.7	1.00	1.00	1.00	0.95	0.65	0.03
	0.65	1.00	1.00	1.00	0.91	0.51	0.01
	0.6	1.00	1.00	0.99	0.83	0.38	0.01
	0.55	1.00	1.00	0.97	0.74	0.27	0.00
	0.5	1.00	0.99	0.95	0.62	0.17	0.00
	0.45	1.00	0.98	0.90	0.50	0.10	0.00
	0.4	0.99	0.95	0.83	0.37	0.05	0.00
	0.35	0.99	0.91	0.74	0.25	0.03	0.00
	0.3	0.97	0.85	0.62	0.15	0.01	0.00
	0.25	0.94	0.76	0.47	0.08	0.00	0.00
	0.2	0.89	0.62	0.32	0.03	0.00	0.00
	0.15	0.80	0.46	0.18	0.01	0.00	0.00
	0.1	0.65	0.26	0.07	0.00	0.00	0.00
	0.05	0.40	0.09	0.01	0.00	0.00	0.00
RoF 12
Code:
		1	2	3	5	7	10	12
	0.95	1.00	1.00	1.00	1.00	1.00	0.98	0.54
	0.9	1.00	1.00	1.00	1.00	1.00	0.89	0.28
	0.85	1.00	1.00	1.00	1.00	1.00	0.74	0.14
	0.8	1.00	1.00	1.00	1.00	0.98	0.56	0.07
	0.75	1.00	1.00	1.00	1.00	0.95	0.39	0.03
	0.7	1.00	1.00	1.00	0.99	0.88	0.25	0.01
	0.65	1.00	1.00	1.00	0.97	0.79	0.15	0.01
	0.6	1.00	1.00	1.00	0.94	0.67	0.08	0.00
	0.55	1.00	1.00	0.99	0.89	0.53	0.04	0.00
	0.5	1.00	1.00	0.98	0.81	0.39	0.02	0.00
	0.45	1.00	0.99	0.96	0.70	0.26	0.01	0.00
	0.4	1.00	0.98	0.92	0.56	0.16	0.00	0.00
	0.35	0.99	0.96	0.85	0.42	0.08	0.00	0.00
	0.3	0.99	0.91	0.75	0.28	0.04	0.00	0.00
	0.25	0.97	0.84	0.61	0.16	0.01	0.00	0.00
	0.2	0.93	0.73	0.44	0.07	0.00	0.00	0.00
	0.15	0.86	0.56	0.26	0.02	0.00	0.00	0.00
	0.1	0.72	0.34	0.11	0.00	0.00	0.00	0.00
	0.05	0.46	0.12	0.02	0.00	0.00	0.00	0.00
RoF 15
Code:
		1	2	3	5	7	10	15
	0.95	1.00	1.00	1.00	1.00	1.00	1.00	0.46
	0.9	1.00	1.00	1.00	1.00	1.00	1.00	0.21
	0.85	1.00	1.00	1.00	1.00	1.00	0.98	0.09
	0.8	1.00	1.00	1.00	1.00	1.00	0.94	0.04
	0.75	1.00	1.00	1.00	1.00	1.00	0.85	0.01
	0.7	1.00	1.00	1.00	1.00	0.98	0.72	0.00
	0.65	1.00	1.00	1.00	1.00	0.96	0.56	0.00
	0.6	1.00	1.00	1.00	0.99	0.90	0.40	0.00
	0.55	1.00	1.00	1.00	0.97	0.82	0.26	0.00
	0.5	1.00	1.00	1.00	0.94	0.70	0.15	0.00
	0.45	1.00	1.00	0.99	0.88	0.55	0.08	0.00
	0.4	1.00	0.99	0.97	0.78	0.39	0.03	0.00
	0.35	1.00	0.99	0.94	0.65	0.25	0.01	0.00
	0.3	1.00	0.96	0.87	0.48	0.13	0.00	0.00
	0.25	0.99	0.92	0.76	0.31	0.06	0.00	0.00
	0.2	0.96	0.83	0.60	0.16	0.02	0.00	0.00
	0.15	0.91	0.68	0.40	0.06	0.00	0.00	0.00
	0.1	0.79	0.45	0.18	0.01	0.00	0.00	0.00
	0.05	0.54	0.17	0.04	0.00	0.00	0.00	0.00
RoF 20
Code:
		1	2	3	5	7	10	15	20
	0.95	1.00	1.00	1.00	1.00	1.00	1.00	1.00	0.36
	0.9	1.00	1.00	1.00	1.00	1.00	1.00	0.99	0.12
	0.85	1.00	1.00	1.00	1.00	1.00	1.00	0.93	0.04
	0.8	1.00	1.00	1.00	1.00	1.00	1.00	0.80	0.01
	0.75	1.00	1.00	1.00	1.00	1.00	1.00	0.62	0.00
	0.7	1.00	1.00	1.00	1.00	1.00	0.98	0.42	0.00
	0.65	1.00	1.00	1.00	1.00	1.00	0.95	0.25	0.00
	0.6	1.00	1.00	1.00	1.00	0.99	0.87	0.13	0.00
	0.55	1.00	1.00	1.00	1.00	0.98	0.75	0.06	0.00
	0.5	1.00	1.00	1.00	0.99	0.94	0.59	0.02	0.00
	0.45	1.00	1.00	1.00	0.98	0.87	0.41	0.01	0.00
	0.4	1.00	1.00	1.00	0.95	0.75	0.24	0.00	0.00
	0.35	1.00	1.00	0.99	0.88	0.58	0.12	0.00	0.00
	0.3	1.00	0.99	0.96	0.76	0.39	0.05	0.00	0.00
	0.25	1.00	0.98	0.91	0.59	0.21	0.01	0.00	0.00
	0.2	0.99	0.93	0.79	0.37	0.09	0.00	0.00	0.00
	0.15	0.96	0.82	0.60	0.17	0.02	0.00	0.00	0.00
	0.1	0.88	0.61	0.32	0.04	0.00	0.00	0.00	0.00
	0.05	0.64	0.26	0.08	0.00	0.00	0.00	0.00	0.00
For high RoF values, your best bet is to assume each "hit" is actually multiple bullets, and use an appropriate RoF table. For example, if you had RoF 100, you could assume each hit is actually 5 bullets and use the RoF 20 table. Optionally, you can divide each step up for a better spread. So, with the above example of RoF 100, and let's say 50% hit chance, you have 15 hits on 1.00, 25 on .99, and 35 on .94, when using RoF 20 and multiplying hits by 5. We can divide the range between 25 and 35, for 27 on .98, 29 on .97, 31 on .96, and 33 on .95. Do this on a case-by-case basis when it really matters if you hit with more rounds than the normal resolution (5/hit in this case) would give.

We'll finish up next post, with some special considerations.
Varyon is offline   Reply With Quote
Old 09-05-2013, 04:07 PM   #3
Varyon
 
Join Date: Jun 2013
Default Re: GURPS Overhaul - Rate of Fire

The First One's Free: Realistically, the first round in a burst shouldn't suffer from Spread. Optionally, if the attack roll succeeded, the first round automatically hits, regardless of spread, while if the attack roll failed, the first round automatically misses. For the remaining shots, you can either use an RoF table corresponding to an RoF one lower, or use the weapon's normal RoF table and assume a minimum of 1 hit (on success) or 1 miss (on failure), it won't particularly break anything.
Note this doesn't apply to weapons firing multiple projectile loads, like a shotgun. For those, just use the normal spread rules. Note also that my later examples don't use this option - not because I don't like it (I do), but because it's quicker to write and get a point across without it.

GURPS Rcl: A possible way to generate Spread values for weapons would be to base them off Rcl. 1/1000 radians (Spread -12) is probably what weapons with high cyclic bursts have, so this is probably fair for Rcl 1. We can then add +3 to Spread per additional Rcl - so Rcl 2 is -9, 3 is -6, 4 is -3, 5 is +0, and so forth. This puts shotgun spread at a little better than Rcl 5, which doesn't strike me as being too terribly off.

Minute of Angle: At very long ranges, even single shots suffer from spread. Based on the skill limitations from Tactical Shooting, Spread due to MOA is -6-(Acc*2). So, Acc 0 is -6, Acc 1 is -8, Acc 2 is -10, and so forth. This replaces the skill cap from Tactical Shooting. Match-Grade ammunition improves Acc for these purposes.
If you have a real-world weapon you want to convert, Spread can be determined by 1/(MOA*pi/10800). This will give you the Range at which the spread is equal to SM+0, convert to a penalty and subtract 6 from this to get Spread. Incidentally, if you take this penalty, make it positive, and subtract 10, you'll get the weapon's GURPS Acc. Bear in mind that most MOA values are for a weapon using Match-Grade (+1 Acc) ammunition!

Multiple Spreads: Some weapons potentially have multiple Spread values at once. A good example would be the shotgun, where each round fires multiple projectiles with their own spread, but each round has its own spread relative to previous rounds. This is also true of weapons with high cyclic bursts (where they have Spread -12 - Rcl 1 - for each burst, and probably Spread -8 - Rcl 3 - or so between bursts). In fact, at long ranges (or with low Acc weapons), Spread due to MOA can come into play! How do we resolve such attacks? If the range is such that only one would even come into play, we'll just use that. For example, say we're using a weapon with Spread -12 bursts and Spread -8 between bursts. We're firing 3 3-round bursts. At Range+SM -8 or greater, we hit with all or nothing. At -12 or greater, we use Spread -8 and RoF 3, multiplying any hits by 3 (as at this range the rounds haven't spread enough to matter).
Things get complicated once both Spread values come into play. Probably the easiest way to handle this is to first use the higher Spread (and low RoF, as above). Assume each "hit" is MoS 0 for the lower Spread. If you hit with all shots, and your roll is half or less of the target number, assume each "hit" is MoS 1. If you miss with all shots, but your roll is less than double the target number, assume MoF 1. If you miss with all shots and your roll is double the target number, assume MoF 2. Optionally, each halving/doubling of the target number gives +1 to MoS/MoF. Back to our high-cyclic burst example, let's say we're at SM+Range -15. So, we'll use our RoF 3, Spread -8, which gives us a 25% hit chance with MoS 0. We roll d% and get .14, good enough for 2 hits at MoS 0. So, now we're looking at MoS 0 for RoF 6, Spread -12. That gives us a healthy 75% hits, so we roll on the RoF 6 table (not listed above, unfortunately) and roll a .91, which ends up giving us 3 hits.
If you are at a range where 3 Spread values come into play, simply follow in sequence. Let's assume our weapon from the above examples has Acc 5 (MOA Spread -16), and engage at SM+Range -20. Our RoF 3, Spread -8, only gets 1% hits at best, which our tables don't bother with. Since RoF is low, we'll just roll d% 3 times. Let's say we get incredibly lucky and roll .01 once, getting us a single hit at MoS 0. MoS 0 for Spread -12 gets us 25% hits at RoF 3. We roll d% and get .61, for 1 "hit" at MoF 1. This gives us a 15% chance at RoF 1, meaning we just roll d% against .15 and hope we manage a hit!
If you use The First One's Free, use your actual MoS/MoF for the automatic (hit/miss) shot.

Modifying Spread: A few options should be available to increase or decrease spread. An easy one is applying a choke to a shotgun - it gives -1 to Spread. Recoil compensators would also reduce Spread - an easy assessment would be to just say -1 to Spread. Strength should also be able to play a role, but this is going to be complicated, as MinST is often based more on the weapon's weight than its recoil, and heavier weapons "feel" less recoil than light ones (assuming they fire the same round). The following is a possible option:
Calculate BL for the weapon's MinST. For a weapon wielded in one hand, divide BL by 20 - for two hands, or weapons with mounts, divide by 10. Add this value to the weapon's empty weight to get its base "Recoil Absorbance" (RA). When the weapon is actually in use, find its new RA (adding the weight of accessories, ammunition, etc, and using the user's ST). Every multiple of RA gives -3 to Spread (so -3 at 2xRA, -6 at 3xRA, -9 at 4xRA, etc), which works out to -1 per RA/3 above the base.
As an example, let's look at the F.R. Ordnance MC-51 (TS 63), with empty weight 10.8, MinST 11, and Rcl 3. This gives us a base RA of (10.8 + 2.4)=13.2, and a Spread of -6. Fully loaded (12.5 lb) and wielded by a character with ST 18 (6.5), its RA is 19 (5.8 above base), for a -1 to Spread. Note you should use the weight of ammunition at the end of the burst for this calculation.
Of course, sometimes you actually want to increase Spread. This is accomplished by moving the weapon purposefully while firing. This actually increases MOA Spread, so if you boost it enough be prepared for multiple rolls! In theory, you could add any amount to Spread. More practically, you're unlikely to gain more than about a foot of spread per yard or so, as moving more than this would result in loss of Acc. If you're willing to get rid of Acc, you could gain as much as a yard per yard of range. Retaining Acc gives maximum MOA Spread of 3, getting rid of it gives maximum MOA Spread of 6.

Beam Weapons: Beam weapons are exceedingly accurate, and the only "spread" they suffer is attenuation, which results in decreased damage and armor penetration rather than fewer hits. By default, such weapons have Spread -(infinity). However, they still have MOA-based Spread (and this can be increased, as noted above).
Beam weapons are typically designed to compensate somewhat for their user's movements. If this option is active, MOA-based Spread cannot be increased. Additionally, if Spread comes into play, roll as though you had RoF 1 and multiply by the number of shots. Note the only way to hit with a fraction of shots is if you get (or start) off-target.
Drilling through armor: Some beam weapons have the option to compensate even more, allowing the beam to continuously hit exactly the same location. When using a weapon in this mode, use the normal rules for compensation, but with two modifications. First off, an initial miss will mean you never hit, regardless of how well you compensate, because it means the weapon is "locked on" to the wrong target. Secondly, upon a successful hit, MoS determines how many shots hit exactly in the same location. Hitting exactly the same location means you add 1/2 the damage of the shot to the damage of the first. MoS 0 means 2 shots hit exactly the same location (so use the damage of one and half the damage of the other), MoS 1 is 3 shots, MoS 2 is 5 shots, and so on, following the SSR table. Shots that fail to hit in the same location do damage normally.

Boomstick Range: Multiple projectile loads - including high-cyclic bursts - follow special rules. If SM+Range is greater than Spread, the rounds of a single shot (or burst) hit closely enough together (in time and space) to count as a single hit. Assess DR normally, halve penetrating damage, and add them all together to determine the wound's severity. For simplicity, it may be best to simply determine penetrating damage once, halve it, and multiply by the number of rounds.

Dodging: Dodging retroactively affects the initial MoS. Multiply Dodge MoS by 2, and apply this as a penalty to the attack's MoS (if Dodge MoS is 0, instead subtract 1 from the attack's MoS). A normal Dodge cannot drop an attack below MoF 1. An Acrobatic Dodge can drop an attack to MoF 2, a Retreating Dodge (provided the retreat is lateral) can drop an attack to MoF 3 but doesn't give a Dodge bonus. A Dodge and Drop similarly can drop an attack to MoF 3 and does give a Dodge bonus. If the attack already failed, a successful Dodge of any sort results in -1 to MoS and ignores the above limitations. The penalty due to Dodge is also suffered by the roll to stay on-target, in which case no limitation on MoF is assessed.
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Old 09-06-2013, 10:21 AM   #4
Varyon
 
Join Date: Jun 2013
Default Re: GURPS Overhaul - Rate of Fire

I had a few further considerations about this variant last night, so I'll post what I can remember...

Very Low Hits: The tables only deal with hits that are multiples of 5%, meaning other probabilities should be rounded to the nearest .05. However, what happens when you have 1% hits? Rounding to the nearest .05 gives us .00, meaning no hits, even if you were firing a million rounds! In these cases, the best option would be to multiply your probability by something that will make it a multiple of .05, and divide your RoF by the same factor. With the way probabilities work, this isn't entirely accurate, and it also means a reduced spread of possible results, but the average stays the same and results are within error, so it's close enough. With our 1% RoF 1,000,000 example, we could instead go with 5% RoF 200,000, 10% RoF 100,000, 50% RoF 20,000, or plenty of others. With a ridiculously high RoF, you'll want to combine this with the option to have each "hit" be multiple bullets (so go with 50% RoF 20, and each hit is 1000 bullets).
Note you could even use this with higher probabilities. If you have 5% with RoF 20, 50% RoF 10 will give comparable results. You can opt to give your players the option to do this, down to RoF 1, meaning they can decide how much range of hits is there (it's a gamble - you can go with just the straight average, or you can hope for more hits and roll for it, at the risk of getting fewer hits). Your best bet may be to err on the side of drama - if the average number of hits would kill/incapacitate an important character/object, feel free to require rolling!

Walking the Burst: The roll to stay on-target handles this in a given round (because it's possible to compensate well enough to get more on-target), but what about between rounds? If continuously firing a weapon at the same target, you can opt to simply try to keep it on-target each round. Don't roll to hit, only roll for staying on-target, using your MoS from the previous round as the base. Your weapon's Acc bonus may no longer apply - use the rules for Follow-Up Shots and Walking the Burst from Tactical Shooting. So, let's say you're firing a tripod-mounted RoF 30 HMG at an armored vehicle. The first round, you hit with MoS 1, then fail your roll to stay on-target by 3, dropping to MoF 2. The next round, you could opt to try and stay (or, rather, get back) on-target. You make your Walking the Burst roll, allowing you to retain full Acc (otherwise you'd be working at half Acc). Your initial roll is counted as automatically being MoF 2, then you roll to stay on-target, succeeding by 5 and getting to MoS 3. Next round, you could try for the same.
For truly walking the burst (for the purpose of hitting other targets), you have a few options. One would be to simply use the Walking the Burst rules from Tactical Shooting as-is (thus allowing you to just skip Aiming first). Another would be to measure the distance between your first target and your second and convert to SM to determine how far from the second target you start (assume MoS 0 against first target). For example, let's take two humans (SM 0) that are 5 yards apart. You start shooting at the first, and end up at MoS 1 when all is said and done. The next round, you opt to walk the burst over to the second. SM 0 is a 1-yard sphere, so MoF 1 is a 1.5-yard sphere, MoF 2 is 2 yards, 3 is 3 yards, 4 is 5 yards, 5 is 7 yards. You're 5 yards away from a 1-yard target, meaning you're hitting within a 6-yard sphere, for MoF 5. This is where you start.

Reducing Tracking Error: Ask any soldier - for best accuracy, you want to limit yourself to short bursts. Under this system, the reason you want to do this is due to the potential for tracking error - getting off-target during the shot. When firing at less than full RoF, multiply your MoS/MoF on your roll to stay on-target by the fraction of RoF. Thus, at half RoF, cut the MoS/MoF in half, and so forth. In our Walking the Burst example above, let's say the soldier is firing his weapon at RoF 15, rather than the full RoF 20. His initial failure by 3 is reduced to 1.5, meaning MoF 0.5. His later success by 5 is reduced to 2.5, meaning MoS 2.
For dealing with the fractional values this produces, you have two options. One is to simply round (but keep it in mind if you opt for Walking the Burst), so our above MoF 0.5 becomes MoF 1. Alternatively, you can automatically round it up (meaning even n+0.0001 becomes n+1), but weight the result by the fraction when determining average (in our above example, determining average would be [MoS 1]/2.5+[MoS 0]/2.5+[MoF 1]/5).

Hitting the Wrong Target: Even when you are dead-on on your target, you may have some bullets miss... so where do they go? As noted previously, targets are approximated as spheres of their SM (a 1-yard sphere for an SM+0 human). You can determine how many SM's apart a target is from another using the same methodology used for Walking the Burst, and note that this is how many more "steps" on MoF they are from the initial target. Note the outer limits of the target correspond to MoS 0, so start at this point!
Optionally (very optionally), you can opt to roll 1d6 to see in which direction (left, right, up-left, up-right, down-left, down-right) your point of aim scatters from the center. Enemies in the same direction are at reduced MoF, enemies in in the opposite direction are at increased MoF.
Let's look again at the example of 2 targets standing 5 yards apart. Our gunner has MoS 2 against the primary target. Not considering scatter, we reduce this to MoS 0 and find the secondary target is at MoF 5. If we consider scatter, MoS 1 means within a 0.7 yard sphere around the primary target's center of mass. If we scatter in the same direction as the secondary target, this means we're 0.35 yards closer than our original calculation of 6 yards (not enough to make a difference). If we scatter in the opposite direction, this means we're 0.35 yards further away (again, not enough to make a difference). Were we instead at MoF 3 (within a 3 yard sphere) against the primary target, scattering in the same direction would mean we are 1.5 yards closer to the secondary target, dropping range to 4.5 (effective range 5) and thus MoF to 4. Scattering in the opposite direction means we are 1.5 yards further away, increasing range to 7.5 (effective range 10) and MoF to 6.
If targets are at the same height and you roll up-right, down-right, etc, halve difference it makes. Ideally, you should instead roll 1d8 (assuming you have one), allowing for all cardinal directions and their 45-degree equivalents.
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