Life and stuff

From: “Stuart Slade” <shiva06804@yahoo.com>
Date: Thu Sep 12, 2002 08:30:11 AM US/Pacific
Subject: More mortar data (and request for EF)

I’ve been doing some research on mortar ammunition. The bulk of what follows comes from a Chinese company called Norinco but I’ve compared it with data from other companies in the same line of business and the information is consistent. Norinco are the world’s largest producers of mortars and ammunition. (They were also very helpful - a kind word about their products in the next book would be a nice gesture.)

Mortar ammunition.

Mortar bomb components are made of (in order of frequency) cast iron, forged steel and cast aluminum. Of these, cast iron is by far the most common - production of cast iron mortar bombs exceeds the combined total of steel and aluminum by an order of magnitude. Put another way, 90 percent of all mortar bombs are made of cast iron. Its low-grade cast iron (we’ll come back to that later). The two primary components of the bomb are the body (the business end that contains the filling) and the tail. Now, there is no reason why the construction of the bomb cannot be mixed (for example, a cast iron body with a cast aluminum tail). Such combinations are used for specific purposes.

All mortar bombs made by Norinco are fin-stabilized. Rifled mortars are extremely rare (only one type in production) and their ammunition is even rarer. Only France produces rifled mortar rounds and licenses production to Turkey.

The obturator rings around the middle of the body are (these days)made of a thermoplastic resin. Older mortars use strips of leather or cloth filled with grease (usually packed with material such as sand or grit to give it mass). The key here is to provide a flexible seal between the mortar bomb and the tube.

On the subject of bomb propellants, mortars are extremely tolerant of varying grades and qualities of explosives. In radical contrast to the assertions made earlier, black powder is extensively used as a mortar propellent both in the primaries and incremental charges. In fact, the characteristics of black powder make it quite advantageous for mortar propellents. The standard primary on a Norinco 120 millimeter mortar is 40 grams of black powder. Other types are available depending on requirement but black powder is a known, used and accepted propellent for mortar bombs. The incrementals weigh a few tens of grams each and are horse-shoe shaped bags that fit around the mortar tail stem. the primary goes inside the mortar tail stem. The problem with black powder (and the reason why sophisticated producers such as Hirtenberger, Soltam or Pyrkal don’t use it) is not fouling or explosive characteristics but degradation. Black powder primaries and incrementals tend to deteriorate quickly under field conditions if not properly cared for. Also, there are safety concerns with black powder that don’t exist with other propellents. Be that as it may, the cheapness and favorable explosive characteristics of black powder still make it attractive. Again, its a known propellent for drop-fired mortars.

We didn’t really cover fuzes or firing systems since these would have to be improvized.

On mortar tubes, the production of improvized mortars and their ammunition is something that is taught to all units of the Chinese People’s Militia (NOT to be confused with the Chinese People’s Liberation Army). The Militia is expected to be able to improvize its own mortars and ammunition using the resources of a Chinese farming village. Apparently, they do so (how successfully is another matter - it would have been impolite to ask). However, the key point is that industrial high-grade piping (hi-grade by Chinese standards) is perfectly adequate for use as a mortar tube. This suggests that Grantville can avoid the bimetallic problem simply by eliminating reinforcement of the tube. Again, we’re not dealing with a high-pressure weapon here - for the sort of ranges we’re talking about (a Norinco 120 with its 40 grams of black powder primary will throw a 16 kilogram bomb about 1200 meters with a muzzle velocity of less than 70 meters per second. At P+6 it’ll throw that bomb 5,700 meters with a muzzle velocity of 272 meters per second.) All mortars foul like crazy and black powder propellent using ones are no better or worse than any others. Drop-fired mortars are extremely tolerant to fouling because the very loose fit of the round going down the tube makes obstruction irrelevant - going up the obturator bands remove loose fouling. Cleaning mortars after prolonged firing is a hard, dirty task (the guy I was talking to had commanded a CPLA mortar battalion)

I mentioned wooden jacketing of the tube - that was regarded as an acceptable insurance policy and (something I hadn’t thought of) it makes attaching carrying handles, training and elevating equipment etc much easier.

Baseplates are made of scrap steel reforged and stamped.

The key point about this is that the primary objections to the drop fired mortar design - the explosive characteristics and fouling from black powder has just gone away. There is no objection to using black powder because it IS used. I would say that we can now discard the heavy cast bronze reinforcement and replace it with a much lighter strapped wooden jacket - again avoiding a lot of problems.

Oh, yes. Fragmentation. The low radius of burst for fragments is a serious problem. We can get around that by making the mortar bomb case much thinner (mortar bombs are not overly stressed in firing so we can get away with that. The reason why mortar bomb body casings are thick is to give lots of metal for fragments). We can make up for the loss of fragments by putting notched cast iron rods parallel to the axis of the bomb and lined up against the inside of the bomb case. Norinco use this instead of notched wire - its cheaper, requires less production time and is almost as satisfactory.

Two other things come out of these conversations. One is its really essential to stop using the US four-deuce as a design baseline - this was a unique, weird and freakish design that was not typical of standard design practice. The other is to stop using data on cannon as a source. Mortars are not cannon; they work entirely differently. Charles used the comparison of First World War fighters for air war/Vietnam. I’d put it much more strongly; trying to use civil war cannon data to discuss drop-fired (not Stokes please) mortars is like using information on the archers at Agincourt to prove the precision guided munitions used in Desert Storm don’t work.

From: “Stuart Slade”
Date: Thu Sep 12, 2002 12:05:26 PM US/Pacific
Subject: More mortar data (and request for EF)

Didn’t take long. T’was in the specification sheets for the ammunition. Potassium nitrate sulphur charcoal mix to US Military Standard Mil-P-223B. By the way, weight of “western incremental” 70 grams, weight of Norinco incremental, 200 grams.

As to the white cloud. Check this photograph

http://www.kimsoft.com/korea/chinese8.jpg

Note the clouds of white smoke around the two mortars in the background - and these are 60 millimeter mortars, not 120s. Remember also the small amount of powder used. Again, consistent with black powder being used as the propellent.

Give it up Kim, you’ve lost this one.

From: “Stuart Slade”
Date: Mon Sep 16, 2002 07:53:17 AM US/Pacific
Subject: More mortar data (and request for EF)

I didn’t actually elaborate on why I needed the data; just asked about the technologies. I’m in the sort of work where I ask odd questions and usually get answers. My guess is that the people I asked assumed I was checking out the possibility of terrorists building improvised mortars.

One interesting thing I learned; we’re talking about using obturator rings to get a gas seal. there is a different way of doing this that’s slick. Instead of an obturator ring, we take a two inch section of the bomb body casing and machine a series of semicircular rings around the body (like a screw thread but individual rings not a spiral). The cute thing is that when this is fired, the gas flow past the bomb from the propellent hits those rings and becomes extremely turbulent. That turbulence also acts as a gas seal.

By the way, can I ask a favor; I’ve been away for three days and a lot of this thread seems to have vanished. Did I miss anything important?

From: “Stuart Slade”
Date: Thu Sep 12, 2002 10:09:30 AM US/Pacific
Subject: More mortar data (and request for EF)

The incrementals depend on the manufacturer and the configuration of the mortar. Most western producers of ammunition do not use black powder because of the deterioration (presumably water absorption) and safety issues (black powder can explode spontaneously due to internal friction - in the good old days nobody cared very much; we do now). However, Norinco and the more remote of manufacturers use black powder for their primaries and incrementals. The standard 120 millimeter mortar incremental from Norinco is 200 grains of black powder.

Its interesting to note that most shots will go much further than people believe. For example, an experiment was done with the 120 millimeter cannon on an M1A1 battle tank. The barrel was elevated to optimum elevation and fired - the explosive shell landed 80 kilometers away. Even a tiny and “juiceless” cartridge like the .22 long rifle is lethal at up to a mile and will probably go a lot further. When I lived in the UK, a woman was killed while standing on the roof of her house - she had been hit in the head by a 7.62 millimeter rifle bullet fired from an army range 7 miles away. A hi-lo pressure grenade from an M79 will go to an absolute distance of something like 2200 meters even though its propulsion charge is tiny (the rated range is 300 meters)

So I find no problem in accepting the primary range of a Norinco 120 (accepting those are range figures used to sell the weapon. - I would think they are accurate but - aahhhh - idealized). My guess is that service range under those conditions would be around 100 - 1000 meters. Entirely adequate for what we want.

Sorry about the mix of metric and imperial - thats what happens when we use sources from all over the world.

From: “Stuart Slade”
Date: Thu Sep 12, 2002 10:42:43 AM US/Pacific
Subject: More mortar data (and request for EF)

In addition to the above, I’ve been reading through the specs of mortar bombs from a round the world and there is an interesting pattern. The Western bombs tend to be thrown about two to two and a half times further for the same charges as those made in Eastern Europe and other parts of the world. Looking at the figures, my guess is the Norinco range quoted is for pure black powder and the “western range” (for example, Thales make a 17 kg bomb that is thrown 10,500 meters on P+6 to give a muzzle velocity of 330 meters/sec).

I also have figures for 120 millimeter bombs made by Militar Rio Tercero. They use a 30 gram black powder primary that throws a 17 kilogram bomb 1050 meters at a muzzle velocity of 105 meters/sec. That seems consistent with the Chinese figure

By the way, reading my notes, China also makes a Type 71 100 millimeter mortar that throws an 8 kilogram round to 4750 meters at P+5 for 250 m/sec.

Overall, it looks to me that the superior range and muzzle velocity of the western mortars and bombs is achieved by using double-base propellent and indicates the sacrifice Grantville is going to make by adopting the Norinco et al black powder based technology. So, (fingers crossed tightly) we now know what we can do with black powder drop-fired mortars and the performance penalties we are suffering from the lack of “proper” propellent

From: “Stuart Slade”
Date: Mon Sep 16, 2002 09:15:26 AM US/Pacific
Subject: Re: More mortar data (and request for EF)

Many thanks.

A thought on ammunition. The big problem we have is the low lethality of the black powder bombs (assuming we use a 100 millimeter tube, that suggests a 9 kilogram bomb with about 1 kilogram of black powder as charge.

In WW2 it was discovered that the addition of aluminum powder to the explosives used in aircraft bombs resulted in a 40 percent increase in yield. Would the addition of aluminum powder to black powder be (a) practical and (b) effective? If we have a double yea on this, it might be an interesting way of overcoming one problem as a stopgap until we get better HE.