Warhead data

[nuke11]

Ok, the problem you have at the moment is the document is based on TNT equivalent of an RE of 1.00. The game uses C4 as it's equivalent for an RE of 1.00 and TNT has an RE of 0.75 in the game.

You will need to adjust all of the formulas from the document accordingly.

Doesn't the M67 have a solid steel case that also needs to be taken into account for the fragments? Here is a good website that shows what some of the fragments look like: http://machinesforwar.blogspot.ca/2012/03/m67.html

Some more images of the inside of the case and what the fragments look like: http://www.big-ordnance.com/grenades...CutawayM67.jpg and http://www.big-ordnance.com/grenades/loworderM67.JPG

The M26 is the grenade with a spiral wound wire core: http://img.photobucket.com/albums/v1...ut/OR-034A.jpg

[mmartin798]

Originally Posted by nuke11

Ok, the problem you have at the moment is the document is based on TNT equivalent of an RE of 1.00. The game uses C4 as it's equivalent for an RE of 1.00 and TNT has an RE of 0.75 in the game.

You will need to adjust all of the formulas from the document accordingly.

The Gurney equations don't care about the RE at all. It only uses the uses the Gurney constant which does not necessarily correlate with RE. Taking the example of making C4 1.00 and TNT 0.75, we would expect TNT to perform at 75% of C4. But that is not the case. C4 has a Gurney constant of 2530 m/s and TNT is 2438 m/s, which makes TNT perform at 96% of C4. The equation in my spreadsheet uses the approximation of the Gurney constant, which is one third of the detonation velocity. For C4 that works out to 8200/3 or 2733 and TNT is 6900/3 or 2300. That makes TNT 84% of C4, which is closer to the 75% you are looking for already.

Originally Posted by nuke11

Doesn't the M67 have a solid steel case that also needs to be taken into account for the fragments? Here is a good website that shows what some of the fragments look like: http://machinesforwar.blogspot.ca/2012/03/m67.html

Some more images of the inside of the case and what the fragments look like: http://www.big-ordnance.com/grenades...CutawayM67.jpg and http://www.big-ordnance.com/grenades/loworderM67.JPG

The M26 is the grenade with a spiral wound wire core: http://img.photobucket.com/albums/v1...ut/OR-034A.jpg

The method of determining fragment size was an approximation intended to simplify the math and make fragments of uniform dimensions that can be directly plugged into the EFactor equation. While we could take the mass of the case and the diameter of the grenade to determine an approximate thickness and then divide the surface area up into the number of fragments to get the area of the face which is more accurate as to what happens with the case of the M67, we are then stuck with fragments that are essentially flat tiles. There is no diameter that we can reasonably put through the EFactor equation as it is shown in the rules. Even though we can calculate the kinetic energy of these flat tile fragments, that is still not enough information to determine the wound generating capability of the fragments. KE alone has been shown time and time again to bot be reliable in wound cavity calculation. The EFactor used in the rules is similar to wound approximation models for significant number to ballistic rounds. So while the wire core is not what happens with an actual M67, it works better for incorporating with the EFactor of other weapons in the game.

[nuke11]

Ok, what happens if a square wire coil is used instead? From the M26A2 the wire is about 3 mm square and lets assume the coil is fragmented every 3 mm for a 3 x 3 cube how does this impact the results?

http://i.imgur.com/FvWF19q.jpg

[ArmySGT.]

[mmartin798]

A few things change. The fragments are slightly heavier with a mass of 0.21g, versus 0.1g. The M26A2 has 0.16 kg of filler, which is a little less. However, that makes no difference to the initial fragment velocity, which is still 3276 m/s. The larger fragments have a higher EFactor initially of 25.

[mmartin798]

I have been thinking about the way grenade damage is applied in game versus the calculations I have been working with and the killing and casualty causing radius of the M67.

The rules give the M67 a 15m burst radius. The M67 has a killing radius of 5m and a casualty causing radius of 15m. So far they seem in agreement.

3rd edition has 1d20 fragments of Efactor 4 for any one in the burst radius. So wearing resistweave coveralls will keep you safe from fragment damage and you only take the full body damage from the DPW of the filler.

4th edition has number of fragments hitting equal to DoS*(Burst radius - actual radius). So we have Kevin, a Marine recon sniper with STR 26 and no specialization in thrown weapons chuck an M67 at Floyd 30m away, rolls a 37 which hits with a DoS of 3. The grenade explodes 9m from Floyd creating 3*(15-9) or 18 fragments with 1+ DoS * 2 or 7 fragments hitting of Efactor 4 each. Again the resistweave coveralls are great.

Using the real world data, assuming uniform fragment distribution, 1335 fragments disbursed and an human silhouette are of about 0.8m^2, we have 4.2 fragments hitting that silhouette at 5m with an Efactor of 17. At 10m we have 1 fragment with an Efactor of 14. At 15m, we have 0.5 fragments with an Efactor of 11. So here at 5m, resistweave bring us 3-5 fragments doing 10 dp each, at 10m, that is 1-2 doing 7 dp each and at 15m we have 0-1 fragments doing 4dp.

Clearly the rules don't really represent the real world data well. But are we satisfied with the rules or could they stand a tweak?

[mmartin798]

I can start things off. The 3rd edition rules with their flat 1d20 fragments was always a problem for me. All the grenades in the game are of a vintage that optimized for uniform fragmentation. Some mechanic mimicking the inverse square rule should have been there. 4th edition, with the number of fragments scaled in part by the distance from the grenade is a step in the right direction.

Even though I have not yet gotten a group together to play 4th edition, I do like the idea of the DoS allowing for more spectacular results. While it may not be 100% true to real world, it makes for better story telling.

The damage per fragment is my biggest gripe. The stereotypical room breaching scenario of tossing in a grenade and charging in after it goes off is a viable for any situation using the rules as written. Real world says that it might work for a bunker, but not a wooden building. Doing that would injure or kill the people crouched outside the door waiting to go in when the grenade goes off. As written the rules make Project personnel, who are covered from head to toe in armor with AV 7 or greater assuming they are wearing a helmet, immune from damage if they manage to get the grenade 2.75m away from themselves. That just does not seem right.

I mean, if you have someone with an HP-35 and they shoot and hit this person from 5m away, you will do 2dp someplace. If this same person is 5m from a badly thrown grenade that hits (DoS = 1), using the 4th edition rules there are 10 fragments with 3 that hit doing no damage. Make it an extremely well thrown grenade (DoS = 10), you get 100 fragments with 21 hitting for, no damage. This person is at the edge of the lethal range of the grenade and takes no damage. It just feels off.

[nuke11]

I like the idea of a bit more realism in the game. I would say to continue to develop the expansion of these rules.

The 5 m kill radius needs to be just that in the game for a grenade. The coveralls shouldn't be the get out of jail free card. If the players do something stupid, that needs to be accounted for.