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Porting some of the Call of Cthulhu 7e combat rules to Basic Roleplaying


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Having finally read the Call of Cthulhu 7e rulebook, I really like some of the innovations it made to the combat rules. Small stuff like Fighting Back to some of the bigger changes like Automatic Fire. And so I did a little brainstorm of how some of these new rules would fit into the old BRP system.

The Fighting Back rules can be easily mapped out to the levels of success that BRP already uses. The main thing I'd probably change would be how ties in that system work, since CoC's levels of success work are calculated differently from BRP. So ties wouldn't lead to the automatic hits for the attacker(if they have the higher skill), it would just be an indecisive engagement and no one gets hit from it.

As for Automatic Fire, I really like how it moves away from making it so powerful in BRP. Maybe the mechanic can be similar, with some adaptations for BRP. The PC starts by sayin how many rounds they want to fire, we then figure out how many rounds the PC can fire in a volley (determined by the skill rating) , then make each volley a separate attack with an increasing penalty(Perhaps in increments of -30%). Each success will mean that half of the shots in the volley hit the target.

What do you guys think? Might be an interesting idea for a document.

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56 minutes ago, KPhan2121 said:

So ties wouldn't lead to the automatic hits for the attacker(if they have the higher skill), it would just be an indecisive engagement and no one gets hit from it.

As I never read CoC7e, I have no idea how those options work, could you explain these?

Anyway, I agree using another method for breaking ties is a good idea. Giving victory to the highest skill gives a huge advantage to the highest skill even if the difference is only 1 point.

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I had to read it many times.. not entirely sur I understand it right! 😮 Oopsie...
So, it seems, for automatic fire, instead of a skill bonus of +5% per bullet / projectile  (must be tired) and the roll the number of hit randomly afterward, just roll normally and if the attack is a success the number of hit is skill roll divided 20 (they use different word, but that's the net result, I think)

 

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16 hours ago, Mugen said:

As I never read CoC7e, I have no idea how those options work, could you explain these?

Anyway, I agree using another method for breaking ties is a good idea. Giving victory to the highest skill gives a huge advantage to the highest skill even if the difference is only 1 point.

Ah, I was working under the assumption that most people knew about the changes in CoC7e.  So I'll try to explain the mechanics in more detail.

The Fighting Back rules gives characters parrying the opportunity to strike back if they rolled a better success then their opponent's attack. In CoC7e, the levels are success are a bit different. Fumbles, Failures, Successes and Extreme Successes(aka Special Successes) are the same as BRP. CoC7e has a new result called a Hard Success, which is rolling equal to or below 1/2 your skill rating. Critical Successes are when you roll a 1 on the die, instead of 1/20 of the skill rating.

When Character A attacks Character B, Character B can either parry or dodge. In BRP, there is no distinction in the results except that parrying doesn't suffer from physical penalties (due to armor and encumbrance) and that parrying weapons can get damaged. However, in CoC7e parrying with a weapon has the distinct benefit in allowing the defender to attack back. So in this situation Character A rolls a Normal Success in his attack roll. If Character B rolls a Hard Success or better, then Character A will take the hit instead. Normally in BRP, a successful parry just negates the attack and may end up damaging one of the weapons. In CoC7e, if Character A and Character B roll the same level of success, then it counts as a tie. In CoC7e, the tiebreaker will be the characters skill ratings with the one with the higher skill getting his attack in. So in the situation where both characters roll the same level of success, and Character A has a skill rating of 60% and Character B has a skill rating of 50%, Character A's attack will bypass Character B's defenses.

This doesn't work for BRP because we don't have Hard Successes, the Lower Skilled Character has to roll at least a special success to even have a chance of blocking an attack from a Higher Skilled Character. There are other rules in the BRP system that CoC7e doesn't have that will require some work to adapt, like being able to parry multiple times (CoC7e only allows you to parry once a turn), weapon lengths are an important part of BRP's melee combat and would have to be factored in somehow, etc.

I hope that explains the Fighting Back rules, I'll be explaining how Automatic Fire works for Lloyd.

13 hours ago, Lloyd Dupont said:

I had to read it many times.. not entirely sur I understand it right! 😮 Oopsie...
So, it seems, for automatic fire, instead of a skill bonus of +5% per bullet / projectile  (must be tired) and the roll the number of hit randomly afterward, just roll normally and if the attack is a success the number of hit is skill roll divided 20 (they use different word, but that's the net result, I think)

 

In CoC7e, Automatic Fire the rules are vastly different from the Autofire rules in BRP. In BRP, you choose the number of shots fired, add +5% for every shot fired and roll a die to determine how many bullets hit the target.

In CoC7e, you would choose the number of shots fired, consolidate the number of shots fired into volleys that would be resolved as separate attacks(with an increasing penalty for every attack after the first one) and that would determine how many shots would hit the target. 

So imagine that a PC has an automatic gun with a skill rating of 60%. He chooses to fire 20 shots at some enemy that he really wants dead. The number of shots that can be put into a volley will be 1/10 of his firearms skill rounded down. So in this example, he can fire 6 shots per volley. Now that we know how many shots he can fire per volley, we can determine how many attacks he will be making, which is 4. The first 3 attacks will each will fire 6 shots, while the 4th one fires only 2 shots. Each subsequent attack will incur an increasing penalty. In CoC7e, this use something called the Penalty Die, its kinda hard to explain how it works but basically it makes you roll with a bunch of dice and you have to take the worse result. Back to the example, the first attack is done at the normal skill rating(after you modify it for other things like range and concealment). The second attack is done with one penalty die, the third attack is done with two penalty dice, and the fourth attack is done with three penalty dice. And so on and so forth. If any of the attacks succeed, half of the shots on the attack would hit (rounding down, to a minimum of 1). So if the PC succeeded on the 1st and 4th attacks, the 1st attack would have 3 bullets hitting their target and the 4th attack would only have 1 bullet hitting the target.

Obviously, adapting the new Automatic Fire rule is going to be a bit more complicated. The main thing I need to figure out is what kind of penalty should each attack incur (my thoughts right now are a cumulative -30% penalty to hit, but that seems too harsh).

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On 5/27/2021 at 8:06 AM, KPhan2121 said:

The Fighting Back rules gives characters parrying the opportunity to strike back if they rolled a better success then their opponent's attack.

Ok, I've seen a similar rule in Tenra Bansho Zero. It's also reminiscent of Pendragon, of course.

As for the tie breaks on skill levels, I still think it's a bad idea. I don't have the time to do the maths, but I think that if a character with skill 99 is opposed to another one with skill 98, the chances that the highest skill wins are above 75%, whereas I think they should be close to 50%.

But, as you explicitly said you don't want to use it, I think it's not worth discussing it here. :)

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On 5/27/2021 at 2:06 AM, KPhan2121 said:

Having finally read the Call of Cthulhu 7e rulebook, I really like some of the innovations it made to the combat rules. Small stuff like Fighting Back to some of the bigger changes like Automatic Fire. And so I did a little brainstorm of how some of these new rules would fit into the old BRP system.

The Fighting Back rules can be easily mapped out to the levels of success that BRP already uses. The main thing I'd probably change would be how ties in that system work, since CoC's levels of success work are calculated differently from BRP. So ties wouldn't lead to the automatic hits for the attacker(if they have the higher skill), it would just be an indecisive engagement and no one gets hit from it.

As for Automatic Fire, I really like how it moves away from making it so powerful in BRP. Maybe the mechanic can be similar, with some adaptations for BRP. The PC starts by sayin how many rounds they want to fire, we then figure out how many rounds the PC can fire in a volley (determined by the skill rating) , then make each volley a separate attack with an increasing penalty(Perhaps in increments of -30%). Each success will mean that half of the shots in the volley hit the target.

What do you guys think? Might be an interesting idea for a document.

         Here's a cool option for handling automatic fire.  Once you have figured out the chance to hit as a percentage, just drop the ones die in the percentile roll (leaving the Tens result) and roll a number of D10's equal to the number of rounds in the burst.  Any roll equal to or under the Tens result on the percentage chance hits. 

         To determine the number of shots a character can take with a weapon in a SINGLE ACTION, just divide the weapons REAL WORLD cyclic rate of fire by 100.  This "ROF" (Rate of Fire), replicates a SHORT BURST like the kind a skilled shooter would take and in the real world would be between one half and three quarters of a second in duration.  The typical length of a burst during an engagement of a single target.   So, an AK with a cyclic rate of fire of 600 would be able to roll 6D10's on a short burst and an MP5 (cyclic rate of 800rpm) could roll 8D10s to hit.  Longer bursts (up to DOUBLE the rate listed) could be fired as well, at a penalty of course.   The number of rounds in the burst will reduce at various range bands due to dispersion of course.  Just divide the ROF in half, rounding all fractions up for each range band past Short Range that you fire into.

        GRAZING FIRE =  Shooting at multiple targets with a burst is known as "grazing fire."  To determine how many meters of terrain you can shoot across, divide the weapon's ROF (the cyclic rate/100) in half (rounding up) and that is the number of 1-meter grids you can cover with a single die roll (1D10) to hit.   

       This should give a pretty realistic level of weapons fire.  

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