Wednesday, August 28, 2013

Massive weapon fire in RPGs

Watched Act of Valor this weekend. It was a 6 hour bus ride to Guadalajara so I had time to watch it and watch it again. I was enthralled by the boat(SWCC) ambush scene when the team is trying to escape on a truck. The ditch it into the river just as the SWCCs turn the river bend and open fire with amazing force against the pursuing forces. I watched over and over again trying to get the feeling of it and transpose that into the game without going crazy with die rolls.

The idea is to create a simple mechanism to represent weapons shooting in excess of 2000 round per minute. The SWCC has:

The GAU-17/A is a variant of the M134 7.62mmx51mm Minigun. Six rotating barrels and an electrically-powered feed system, the GAU-17/A is capable of up to 4000 rounds-per-minute and is a great area weapon used to suppress enemy fire in the case of needing to buy a few minutes of time during a Hot extract.

The Browning M2 is an air cooled, belt fed machine gun. The M2 fires from the closed bolt position. The M2 fires the .50 BMG cartridge, which offers a max effective range of 2000 yards, accuracy and an excellent fire suppression weapon at 1200 Rounds Per Minute.

The M60 is a gas operated, air cooled, belt-fed, automatic machine gun that fires from the open-bolt position and is chambered for the 7.62 mm cartridge.  It has a max effective range of 1000 yards at ~2800 feet per second

Mk19 Automatic Grenade Launcher. The primary ammunition for Mk 19 is the high explosive dual-purpose M430 grenade. Upon impact, the grenade can kill anyone within the radius of five meters, and wound them within the radius of 15 meters.


So far I have worked with just the M249 and a 50 cal mounted on HUMVEEs. But seeing the amazing firepower GAU got me wanting to put it into play, but a bit more than just waiving it as some suppression rule and without going crazy with die rolling. Here's a clip of the scene so you get an idea what I'm talking about.

And another nice video from the Navy showing the craft in action.

Using massive fire power in tabletop RPGs can be a daunting task given that hits are determined by die rolls. At 4000 rounds per minute and ten seconds to the combat round, that's 666 die rolls for all those bullets (what a nice round number that gives [grin]). As appealing as rolling 666 times may sound it is just out of the question in a real game. I'm using a single roll for the attacker and an additional roll for every target to determine suppression, hits and effects of cover.

To do so I'm taking a more statistical approach to the mechanism based on bullet coverage, rate of fire and affected area. The intent is to suppress first, kill later. No one in their right mind will stand up in such a hailstorm of bullets, but they still keep firing, why? To keep them pinned. If someone brave enough or stupid enough were to stick his head out to shoot I want to determine the odds of getting hit. I also want realistic odds of getting hit from the initial surprise attack.

So boat comes in, opens fire, kills as many as possible while the surprise factor is on and enemies are exposed. As enemies take cover they become harder to hit, but not harder to suppress. They will still be forced to tuck in and cover. If someone where to sneak out and try to return fire I want some odds of getting hit, not a simple "surprise, you're dead".

The following table shows the odds for different rates of fire for different area sizes. I'm working on two sizes 10m and 5m, meaning the weapon is continuously swept over either a 10 meter or 5 meter area where enemies are believed to be.

Odds of body impact
Type of Fire Odds of hit Odd for suppression 100% exposed 50% exposed 10% exposed
MG Fire into 10m area 100 RPM 35.47% 66.79% 35.47% 28.27% 9.99%
MG Fire into 10m area 200 RPM 57.53% 81.39% 57.53% 47.04% 9.99%
MG Fire into 10m area 500 RPM 74.76% 95.16% 74.76% 57.53% 16.57%
MG Fire into 10m area 1000 RPM 90.86% 99.11% 90.86% 70.94% 16.57%
MG Fire into 10m area 2000 RPM 97.03% 99.99% 97.03% 78.24% 23.03%
MG Fire into 10m area 5000 RPM 99.38% 100.00% 99.38% 86.72% 23.03%
MG Fire into 5m area 100 RPM 66.79% 86.72% 66.79% 52.43% 16.57%
MG Fire into 5m area 200 RPM 90.86% 97.73% 90.86% 70.94% 16.57%
MG Fire into 5m area 500 RPM 99.59% 100.00% 99.59% 86.72% 23.03%
MG Fire into 5m area 1000 RPM 99.99% 100.00% 99.99% 92.52% 29.34%
MG Fire into 5m area 2000 RPM 100.00% 100.00% 100.00% 97.03% 35.47%
MG Fire into 5m area 5000 RPM 100.00% 100.00% 100.00% 98.75% 35.47%

Odds of hit : the odds of hitting a human size target standing in the area.
Odds of suppression : the odds of any target (under cover or not) of being suppressed and wanting to take and keep cover above any other action.
Odds of body impact : odds of taking a hit given a certain amount of cover. At 100% exposure odds are the same as odds to hit.

As you can see at 4000 rounds per minute the GAU has high odds of taking anything standing in its line of fire that isn't behind solid cover. Popping out to take a shot back at the enemy still gives the GAU high odds of scoring a hit (23 and 36 % depending on size of affected area). Suppression will be great for any weapon firing 500 or more rounds into the area. This will require skill and training to overcome and be able to return fire. To do this the enemy may pop up, aim and shoot, giving more time for the GAU to blow his brains out or simply stick the weapon out and fire blindly at the target.

Those will be covered in the next post related to blind shooting into an area.

Weapons Free is a modern day warfare RPG I'm currently developing. You can join the community to follow on its progress and join playtest sessions.

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