Post/Author/DateTime	Post
#1 tema69 Mar 15, 2008 8:18:49	Hey guys, I need help coming up with some rules concerning the backblast of portable antiarmour weapons. This is especially important indoors. It's for a WW2 Campaign. I know the PIAT (Projector, Infantry, AntiTank) was fireable from inside buildings because it had no significant backblast. But that was about the only reason to use it. Any ideas? Edit: To give you an idea of how it looks like, this is an AT4 firing outside. The shellcasings were laying on the ground prior to the blast of the ATweapon.
#2 aspiring_lichlord Mar 15, 2008 10:58:00	holy crap! Um, when I saw the thread title I was thinking "why just make a 10/20 ft. cone effect behind the launching square and deal 1/2 or 1/4 fire/heat damage to anyone in the way (reflex saving throw, DC 20 for half)" But now... um the above plus some area effect (all around distance equal to backblast cone distance) non-lethal sonic damage; if it exceeds the character's constitution score then they're deafened for x rounds (probably two or three), other wise they're deafened for 1 round. Sonic damage within the backblast cone is lethal and causes automatic deafening for 1d6+1 rounds. Multiply the effects of damage and deafening indoors proportional to the smallness of the room being fired in, adjacent rooms take half deafening damage after magnification and backblast will erupt through doorways; if the backblast cone hits a wall simply add 1/4 to the remaining distance and project it off of the wall, doors can and will be destroyed; smoke effects anything I missed?
#3 backstabbist Mar 15, 2008 12:36:33	Check out the 3rd shell directly inline with the AT4... that one still has a bullet in it! Sq behind: RefDC20, 2d6 Fire (or Sonic when playing Future ) 2nd Sq behind: RefDC15, 1d6 All or None save to shutdoen Evasion, & try to avoid punishing Toughs by having 200 different types of DR/ER they need to take: stick to just Fire to give them guys a break. The game is too coarse for sideblast, and it is already a pain with the lack of 'facing' to determin who is 'behind'
#4 aspiring_lichlord Mar 15, 2008 12:58:38	that works, I nominate backstabbist's version
#5 bitter_thorn Mar 16, 2008 12:19:53	2d6 seems a touch low. http://commons.wikimedia.org/wiki/AT-4 http://www.answers.com/topic/at4 Check out the 3rd shell directly inline with the AT4... that one still has a bullet in it! Sq behind: RefDC20, 2d6 Fire (or Sonic when playing Future ) 2nd Sq behind: RefDC15, 1d6 All or None save to shutdoen Evasion, & try to avoid punishing Toughs by having 200 different types of DR/ER they need to take: stick to just Fire to give them guys a break. The game is too coarse for sideblast, and it is already a pain with the lack of 'facing' to determin who is 'behind'
#6 backstabbist Mar 16, 2008 12:47:41	But it is a game fitting (AGB) amount. Maybe the AT4 Backblast should be very lethal, maybe as lethal as getting shot by a 9mm... so in a game where an known adequately killful gun does 2d6 we would have a hard time making the concussive wave of backblast more killful than a 9mm to the chest. If that seems low, then use the damage for a 357mag with 180bearslugs... which suprisingly is the same as 9mm. 1 square of it being as lethal as getting a 45 in the chest, the next square is as injuring as getting a LouisvilleSlugger in the face.(club 1d6) Remember, the blastwave is exhaust from a propellant charge burn, not a detonation. It may seem like an explosive detonation, but it is a pressure curve burn... just a very quick one ;). The game is way to coarse to try to model the backblast of various bore Recoiless in any detail.
#7 bitter_thorn Mar 16, 2008 13:28:27	I reckon that is a reasonable range given AGB and fire arm damage ranges in game. How would you handle confined space use?
#8 backstabbist Mar 16, 2008 14:11:52	Problem is in the term Confined. Most confined spaces are not truely confined, by openings like windows/halls and similar freeflow vent routes. They also have resrticted vent routes like doors. If a guy shoots a AT4/LAW while in a 10x10 room with 2 windows and a $14 hollowcore door, the door will gladly blow out to vent the overpressure. Most residential walls of 2 sheetrock & some pinkfluff will also gladly give up their existance to release overpressure. It really depends on the durability of the confinement. If you determine an adequately durable confinement, the overpressure damage would be to all in that confinement, the entire room gets overpresured not just a radius from the Recoiless. This damage would be in addition to the direct jet into the 2 sq behind. This also depends on the bore of the Recoiless. A 67mm 3lb uses a lot less charge than a 94mm 30lb, so the relational volume of overpressure would be far less.... and we are talking in 3space so that my adjust numbers as well. For simple funtion math (& simple function math is good math ;)) We could assign 1 point damage for each 10mm bore, FortSave for half DC10+ damage, affecting 2 nominal 5'sq confinement per 10mm bore. And just ratio the nominal:actual confinement space to elevate or diminish the damage from overpressure in realation to extra/shortage volume. 67mm in a 10x10: 7damage to 14SQ nominal, 14SQ:4sq<10x10actual>= 3.5, 7 x 3.5 = 24 confinement damage FortDC34 67mm in a 20x20: 7damage to 14SQ nominal, 14SQ:16sq<20x20actual>= 0.44, 7 x 0.88 = 6 confinement damage FortDC16 94mm in a 15x15: 9damage to 18SQ nominal, 18SQ:9sq<15x15actual>= 2, 9 x 2 = 18 confinement damage FortDC28 Feel free to throw come coefficients in to adjust the Sq per 10Bore or Damage per 10Bore... like I am already looking at making it 1.5 sq per 10Bore instead of 2sq This model takes a lot of the 3space out of the deal, simpler but not as accurate. It requires the GM to make the determination as to the durability of the confinement, and the ceiling height in respect to "normal". It is a AGB quickie, we could get more volumetric if we want, as well as non-linear propellant charge weights.
#9 bitter_thorn Mar 16, 2008 14:33:42	Good reply, Thanks!
#10 ed_209a Mar 17, 2008 8:58:13	If your characters are really well supplied, there is a new AT4 that has greatly reduced backblast effects. Google for the AT4 CS (for "Confined Spaces") It has what amounts to a water balloon in the back of the launcher. The water vaporizes on firing, absorbing the energy that otherwise would create the dangerous blast.
#11 crwydryny Mar 17, 2008 11:08:11	I'm not 100% sure about the AT4 but I know the british MAW-84 and american dragon ATW (which are about the same calibre) have a backblast that coves a cone 4.5m x 3.6m behind the weapon as is about as impresive as the explosion on the reciving end (anyone standing behind the weapon is likely to get killed by the backblast) so I would say treat it like a grenade blast (but only in the area of effect) or like a flame thrower (which ever suits you better)
#12 tema69 Mar 17, 2008 18:46:04	Check out the 3rd shell directly inline with the AT4... that one still has a bullet in it! The photo is taken during a live fire exercise. I guess it's normal that some rounds don't go off or are dropped when loading the belt. But yeah, we'd noticed the unfired round ;D Anyway, you've got some real good rules. Some of them very 'Stabbist-like. ;) Thanks y'all. Feel free to keep posting. :P
#13 aspiring_lichlord Mar 18, 2008 13:37:27	=Scaling backblast damage to the weapon: dice type is same as firing weapon, reflex save DC15 to avoid damage or take full damage on failure, evasion allows taking only half damage on failure, may catch on fire =first square behind firing character/weapon-mount: 2 dice of fire damage, must pass fortitude check of DC (max possible fire damage, 2d6=DC12) or take equal amount of sonic/concussion non-lethal damage =second square behind firing character/weapon-mount: 1 dice of fire damage, must pass fortitude check of DC (max possible fire damage, 1d8=DC8) or take double amount of sonic/concussion non-lethal damage
#14 backstabbist Mar 18, 2008 15:32:19	Scaling backblast damage to the weapon: dice type is same as firing weapon please elaborate/demonstrate
#15 kitsuneyasha Mar 18, 2008 18:21:29	Now I was watching one time some show about weaponry (future weapons?) and they said that it was dangerous to fire them indoors due to the backblast doing something? im not a weapons expert, im going by memory.
#16 nodaisho Mar 18, 2008 21:36:51	I think the idea is that if you fire one without enough space behind you, the backblast will come back at the shooter, and whoever else is in the room with him. edit: kinda like shooting a hose at a wall, I guess.
#17 johannixx Mar 19, 2008 0:14:24	It's concussion. If you set off an explosive inside a room, it's more damaging to the stuff inside it than just being near it in the open. I like to call it the 'chunky salsa effect', after the rule of the same name in Shadowrun.
#18 backstabbist May 15, 2009 11:22:07	Will the PL6 PL7 & PL8 shoulderfire rockets have to deal with backblast?
#19 atanakar May 16, 2009 7:20:04	I've had to opportunity to actually fire, once, a M-72 portable anti-tank missile during my training time in the Canadian Militia. You do not want to be within 10 feet (square) of the back blast. In that zone any idea of a save against damage is futil. No «unaugmented» or heavily armored human being could avoid such damage. We are geneticaly not fast enough... -------- For those who wonder : I managed a direct hit to the right track thus severing it in two. It was nice to see it roll off the wheels. I got passing grades for «Immobilizing the tank». My best budy got to shoot just after me. He actually managed to hit the canon side ways and sent the turret spinning for a full revolution. He got passing grades for destroying the canon.
#20 backstabbist May 16, 2009 10:33:26	In that zone any idea of a save against damage is futil in reference, is that As, More, or Less futile than giving a save vs m67Frag or Claymore at 5' ?
#21 johannixx May 19, 2009 21:26:42	Will the PL6 PL7 & PL8 shoulderfire rockets have to deal with backblast? Saab-Bofors is already making a limited-backblast launcher for urban combat (AT4-CS). Mmmm, recoilless rifle...
#22 atanakar May 20, 2009 9:44:37	in reference, is that As, More, or Less futile than giving a save vs m67Frag or Claymore at 5' ? Its up to you really: http://en.wikipedia.org/wiki/MON-50 The mine has conventional or advanced seismic influence fuzing. It is a hand laid directional fragmentation mine which is normally command actuated (always secure command wires). The MON-50 is known to be used with the VP13 seismic controller which prevents close approach for any clearance operations, or to a variety of BT fuzes. On detonation the mine will normally propel lethal fragmentation to a range between 40 and 60 meters, although the actual hazard range for these types of mines can be as high as 300 metres based on US Army tests of the M18A1 "Claymore" (this is directly in front of the mine, fragmentation range and density drop off to 125 meters to the sides and rear of these mines).
#23 backstabbist May 20, 2009 10:49:24	oh, I'll be the first to agree that explosions are not harmless, but in game terms, where a m67Frag or 155Shell 5' away gives a save and Evasion gives a free pass, one cannot consider 'backblast' to not have the same rules apply to it. So we need to set the scale, the frame of reference, to HOW lethal... More than or less than a m67Frag at the same distance (same dmg & save)? More than or less than a 81Mortar at the same distance (same dmg & save)? More than or less than a 155Shell at the same distance (same dmg & save)? I put it less than grenade due to lack of shrapnel (no, the junk picked up off the floor is not going mach2) Future rockets might go LowRecoil ratherthan Recoiless, ala Gyrojet or AT RifleGrenade: 'Low' Impulse launch followed by the heavy main drive impulse once its out the tube 30'. Thump it out like a shotgun recoil, then it kicks in the big thruster
#24 bone_naga May 20, 2009 16:55:14	I put it less than grenade due to lack of shrapnel (no, the junk picked up off the floor is not going mach2) Agreed. No primary fragmentation, plus low explosives (propellant) instead of high explosives. It should definitely be less than a hand grenade.