Striker Book 3 CBM ammunition

[snrdg082102]

Hello all,

While working on calculating the contact penetration characteristic for a MD gun CBM round I'm not sure I've been calculating the values correctly.

The CPR gun example is for a TL 9 11 cm Medium velocity gun.

Per DS 2 Step L5 CBM the following criteria is presented:

1. The round is available at TL 7
2. At TL 7 contact and fragmentation penetration values are both 6.
3. At TL 8 and higher contact penetration uses the 4 cm HEAP round characteristics, which starts at 6.
4. At TL 8 and higher fragmentation penetration uses the 4 cm HE contact penetration characteristics which starts at 5.

CBM Contact Penetration

Per DS 2 L4 HEAP the round penetration value uses the HEAP Penetration Modifier Table on DST page 8 based on TL and gun type. Tech Level counts down the rows, while and gun types medium, high and hyper velocity count up the rows.

The CBM example appears to start the HEAP Contact penetration value for a 4 cm at 6 and counts down, per the HEAP Penetration Modifier Table, 5 rows.

What happened to the requirement that the HEAP contact penetration is modified by gun type?

 

[shield]

Not sure - as a guess since it is a deployed sub-munition, the gun type does not come into it.

 

[snrdg082102]

Evening shield,

Thanks for the guess, which sounds good since I don't have anything better.

Another item to add to my list of possible errata to submit at the end of my going through Book 3. The other item is that the CBM round in the design sequence doesn't indicate that there is a burst size either. I had to review the AC example on page 30 to confirm the need for the burst size.

Not sure - as a guess since it is a deployed sub-munition, the gun type does not come into it.

Again thank you for the help.

 

[Carlobrand]

Hello all,

While working on calculating the contact penetration characteristic for a MD gun CBM round I'm not sure I've been calculating the values correctly.

The CPR gun example is for a TL 9 11 cm Medium velocity gun.

Per DS 2 Step L5 CBM the following criteria is presented:

1. The round is available at TL 7
2. At TL 7 contact and fragmentation penetration values are both 6.
3. At TL 8 and higher contact penetration uses the 4 cm HEAP round characteristics, which starts at 6.

The HEAP Penetration modifier table on page 8 of the Design Sequence Tables tells you to go down three rows for a TL 7-8 HEAP. For the CBM, the TL 7 HEAP is not an issue since the game directs a modifier of 6 regardless. The TL 8 4 cm HEAP however ends up with a penetration of 15, not 6, unless modified by gun type.

4. At TL 8 and higher fragmentation penetration uses the 4 cm HE contact penetration characteristics which starts at 5.

Errata directs we count down one row for every two tech levels above 6. Ergo, a TL 8 4cm HE starts at a contact penetration of 6.

CBM Contact Penetration

Per DS 2 L4 HEAP the round penetration value uses the HEAP Penetration Modifier Table on DST page 8 based on TL and gun type. Tech Level counts down the rows, while and gun types medium, high and hyper velocity count up the rows.

The CBM example appears to start the HEAP Contact penetration value for a 4 cm at 6 and counts down, per the HEAP Penetration Modifier Table, 5 rows.

What happened to the requirement that the HEAP contact penetration is modified by gun type?

CBMs present a different situation. Rather than being shot from the gun and slapping directly into the side of a target (which historically had a tendency to damage the round before it detonated and resulted in less than optimal yields with higher-power guns), the CBM round is being fired indirectly and falling down on the target from above, and the CBM submunition is being dropped out of the air above the target by the CBM main casing, thereafter falling and hitting the target at whatever the round's (and then the submunition's) terminal velocity might be - or less, depending on how high the main casing is when it dispenses the submunitions. The result is an impact velocity that can be a half to a fifth or less the muzzle velocity of a medium velocity gun (I'm not so good at that math).

The CBM HEAP submunition therefore does not suffer the same degree of impact that it might receive had it been fired directly from a 4 cm gun, so it doesn't take the gun type modification, as shown in the Striker example.

(An interesting side note is that, while they did that for the CBM, the indirect fire artillery does not get this benefit. Take a 4 cm gun and lay down a HEAP artillery barrage, and the HEAP rounds take the gun penalty even though in the real world they'd be dropping from above at a speed much lower than they'd be hitting if the gun were fired directly at something. There's no rule to shield HEAP rounds from the direct-fire gun velocity penalty unless you implement a house rule.)

 

[Timerover51]

I see no reason for any sort of penalty for High-Explosive Armor-Pentrating/Piercing rounds, as they function on the shaped-charge principle, using the Munroe Effect. The 105mm tank gun fired a HEAT round at 3,850 feet per second/1,173 meters per second muzzle velocity, with the assumption that the targets would be around 1500 meters and less, so the impact velocity was going to be very high.

The problem with HEAT rounds (a.k.a. HEAP) rounds is that when a shaped charge is fired from a rifled artillery piece, the shaped charge jet penetration is reduced as it is rotated as well, spreading it out, so that what you get is a wider but shallower penetration. As a consequence, the 105mm tank gun round had a plastic obturator which sealed the gases behind the projectile, but did not impart rotation to it. It relied one the projectile ballistic shape to stabilize the round in conjunction with the high velocity. The HEAT rounds for the 75mm and 105mm artillery pieces had a long thin standoff cone but because of rotation, the 75mm was good for penetrating slightly over 3 inches of armor, and the 105mm was good for a bit over 4 inches.

The other key to HEAT round penetration is stand off distance, the distance from the base of the charge to the target. Optimum stand off distance was determined in WW2 through an extensive series of tests to be 6 times the diameter of the charge. For a 105mm round that would be 630 millimeters or about 25 inches. That is a bit hard to achieve with an artillery round, but you can improve it by putting a Point-Initiating Base-Detonating fuze on an aerodynamic spike to touch the charge off as far from the target as possible. That is why you see a spike on the later version of the TOW missile warhead. It serves to increase penetration.

The problem with the little 4cm bomblets is lack of standoff distance. As a result, their penetration is limited to about one caliber or so, generally the current HEMP (High Explosive Multi-Purpose) rounds for the 40mm grenade launcher at credited with the ability to penetrate 2 inches/50mm of armor, however, the effects behind the plate can get a bit iffy, depending on what is there. If you hit the top of a APC personnel compartment, unless someone is in there, your damaging effect is pretty much limited to the hole. If you hit on the engine compartment, the penetrating jet could easily damage or set fire to the engine.

There are some other wrinkles to shaped charge penetration of armor, like putting a stand off detonating plate a distance away from the armor, or going with a faster detonating higher energy explosive (which may increase the cost by a factor of 10), or changing the metal of the shaped charge cone (which is typically pure copper). One of the best way to protect against top attacks by small caliber bomblets it to put a sheet of plywood about 3 to 4 feet above the area to be protected. That pretty much defeats the bomblet, not just armor penetration, but also casualty fragments.

 

[snrdg082102]

Morning Carlobrand,

My apologies for being unclear and not providing a complete example of the results when I asked my question

Items 3 and 4 are summaries of the base requirements, as I understand them, stated on Striker Book 3 DS 2 L5 page 15 for CBM rounds over their TL 7 introduction I added the starting values assigned to the 4 cm HEAP and HE rounds without applying modifiers.

Yes, my value after applying the modifier of counting down 3 rows for a TL 8 contact penetration value of 15 matches the example used in the reply.

To complete the example presented at the start of the thread a TL 9 11 cm MD medium velocity gun CBM round has a base/unmodified HEAP contact penetration value of 6 which per the HEAP penetration table counts down 5 rows giving the round a final value of 21.

Errata directs we count down one row for every two tech levels above 6. Ergo, a TL 8 4cm HE starts at a contact penetration of 6.

Again completing the TL 9 11 cm medium MD gun example the frag pen would be add 2 to the base value of of a 4 cm round of 5 giving the final value for frag pen of 7.

CBMs present a different situation. Rather than being shot from the gun and slapping directly into the side of a target (which historically had a tendency to damage the round before it detonated and resulted in less than optimal yields with higher-power guns), the CBM round is being fired indirectly and falling down on the target from above, and the CBM sub-munition is being dropped out of the air above the target by the CBM main casing, thereafter falling and hitting the target at whatever the round's (and then the sub-muntions) terminal velocity might be - or less, depending on how high the main casing is when it dispenses the sub-munitions. The result is an impact velocity that can be a half to a fifth or less the muzzle velocity of a medium velocity gun (I'm not so good at that math).

The CBM HEAP sub-munition therefore does not suffer the same degree of impact that it might receive had it been fired directly from a 4 cm gun, so it doesn't take the gun type modification, as shown in the Striker example.

(An interesting side note is that, while they did that for the CBM, the indirect fire artillery does not get this benefit. Take a 4 cm gun and lay down a HEAP artillery barrage, and the HEAP rounds take the gun penalty even though in the real world they'd be dropping from above at a speed much lower than they'd be hitting if the gun were fired directly at something. There's no rule to shield HEAP rounds from the direct-fire gun velocity penalty unless you implement a house rule.)

Here is what I think is the difference, being a submarine sailor and not using artillery, is height above the target. CBM rounds for the most part, at least from my understanding, don't gain the full potential of gravity assist the way indirect fire rounds do. Of course I could be out to lunch.

 

[snrdg082102]

Hello timerover51,

Thanks for the information very neat to know. You may want to take a look at the product title of Guns, Guns, Guns authored by Crag Porter at BTRC (http://www.btrc.net).

I see no reason for any sort of penalty for High-Explosive Armor-Pentrating/Piercing rounds, as they function on the shaped-charge principle, using the Munroe Effect. The 105mm tank gun fired a HEAT round at 3,850 feet per second/1,173 meters per second muzzle velocity, with the assumption that the targets would be around 1500 meters and less, so the impact velocity was going to be very high.

The problem with HEAT rounds (a.k.a. HEAP) rounds is that when a shaped charge is fired from a rifled artillery piece, the shaped charge jet penetration is reduced as it is rotated as well, spreading it out, so that what you get is a wider but shallower penetration. As a consequence, the 105mm tank gun round had a plastic obturator which sealed the gases behind the projectile, but did not impart rotation to it. It relied one the projectile ballistic shape to stabilize the round in conjunction with the high velocity. The HEAT rounds for the 75mm and 105mm artillery pieces had a long thin standoff cone but because of rotation, the 75mm was good for penetrating slightly over 3 inches of armor, and the 105mm was good for a bit over 4 inches.

The other key to HEAT round penetration is stand off distance, the distance from the base of the charge to the target. Optimum stand off distance was determined in WW2 through an extensive series of tests to be 6 times the diameter of the charge. For a 105mm round that would be 630 millimeters or about 25 inches. That is a bit hard to achieve with an artillery round, but you can improve it by putting a Point-Initiating Base-Detonating fuze on an aerodynamic spike to touch the charge off as far from the target as possible. That is why you see a spike on the later version of the TOW missile warhead. It serves to increase penetration.

The problem with the little 4cm bomblets is lack of standoff distance. As a result, their penetration is limited to about one caliber or so, generally the current HEMP (High Explosive Multi-Purpose) rounds for the 40mm grenade launcher at credited with the ability to penetrate 2 inches/50mm of armor, however, the effects behind the plate can get a bit iffy, depending on what is there. If you hit the top of a APC personnel compartment, unless someone is in there, your damaging effect is pretty much limited to the hole. If you hit on the engine compartment, the penetrating jet could easily damage or set fire to the engine.

There are some other wrinkles to shaped charge penetration of armor, like putting a stand off detonating plate a distance away from the armor, or going with a faster detonating higher energy explosive (which may increase the cost by a factor of 10), or changing the metal of the shaped charge cone (which is typically pure copper). One of the best way to protect against top attacks by small caliber bomblets it to put a sheet of plywood about 3 to 4 feet above the area to be protected. That pretty much defeats the bomblet, not just armor penetration, but also casualty fragments.

 

[Carlobrand]

... Again completing the TL 9 11 cm medium MD gun example the frag pen would be add 2 to the base value of of a 4 cm round of 5 giving the final value for frag pen of 7. ...

Add 2 to 5? Now here's a point where maybe someone can answer a question for me. Errata says count two levels per tech level. Do we round up, or down? The autocannon example on page 30 implies up (i.e.7-8, 9-10, etc.), but I've seen other canon sources that looked like they're taking it down. Are we all agreed that the example in Striker is the way things should go, as that one is actually part of that rule book?

 

[snrdg082102]

Evening Carlobrand,

Add 2 to 5? Now here's a point where maybe someone can answer a question for me. Errata says count two levels per tech level. Do we round up, or down? The autocannon example on page 30 implies up (i.e.7-8, 9-10, etc.), but I've seen other canon sources that looked like they're taking it down. Are we all agreed that the example in Striker is the way things should go, as that one is actually part of that rule book?

Sorry about using the word add the proper wording should be move down the rows for the HE round.

In the printing of Striker Book 3 that I have states:

HE penetration does increase with tech level; count down 1 row on the table for every 2 tech levels (or fraction there of) above 6.

From the Consolidated CT Errata

Page 7, CPR Gun Table, Notes, Penetration – HE (correction): The tech level modifiers for HE penetration are wrong. Count down one row for each two tech levels above 6, as stated in Book 3, page 15.

I don't know about anyone else but I have been trying to go up and down the rows, of course I also use the word add which goes down the rows.

I'll try to use down and up on further threads.