Author Topic: powder chamber design (Read 1431 times)

firebuckeye · « **on:** January 23, 2007, 02:25:37 PM »

I was wondering if it is nessasary to have a powder chamber when building a howitzer? What is the purpose of it? And if you were building a golfball howitzer what would be the max powder chamber size? Also how does width and height come into play. For example would the design ever be 1.5 x 1, or should it be same both ways. Hopefully I explained what I am thinking.

Evil Dog · « **Reply #1 on:** January 23, 2007, 03:13:45 PM »

I'm sure that there are several ways to do it, but loading a foiled powder charge in to a sub-caliber hole at the breech end of the bore could be an interesting prospect.

accuratemike · « **Reply #2 on:** January 23, 2007, 04:36:49 PM »

I guess the first decision is to adhere to the "1 caliber thick walls at the breech" rule. Un-chambered, a golfball mortar or cannon would have to be 5 1/4" diameter at the breech. That is a little chunky for the typical howitzers etc. that people are likely to build. A sub-chamber starts to make sense. As far as size, I'm having the same quandry. Looking at the charts and info posted here and elsewhere it is hard to pin down a maximum charge for a 1 3/4" bore gun. A little off the chart from one source and below the 2" of another. I'd like to know what the maximum charge, I need to fit in, as well. With that info it would be easy to come up with the volume required. IE 1/3 OD/bore x "X" length. Anybody recommend a maximum charge with a projectile for a 1 3/4" gun? Which grade of powder? Then is it a simple matter of 2x that for blanks? I think a suitable blank load would mean a deep sub-chamber, I've been pondering "stepped" foil charge.
Regarding loading a sub-chambered howitzer-length barrel with a charge: There must be a way, how were Mt. Howitzers loaded? I'm envisioning a scoop shaped ended charging rod that is turned 180° and removed, leaving the foil charge in the sub-chamber. Maybe with some kind of collar to center it in the bore.
My tube is 4"OD, so I'm assuming a 1 5/16" bore sub-chamber max. That's not so bad.
Figure out the max loads and keep me posted. Good luck, MIKE

Artilleryman · « **Reply #3 on:** January 23, 2007, 04:52:37 PM »

On a full scale Mountain Howizter we are able to push a foil wrapped charge into the chamber without much trouble.

jeeper1 · « **Reply #4 on:** January 23, 2007, 06:03:40 PM »

Here are a couple of scaled powder charges in Fugi? 35mm film cans. On the left is 200 grs of cannon grade and on the right is 100 grs of 3f. The film cans are 1.250 outside diameter and 2 inches tall so you can see you don't really need that big of a powder chamber. Of course a baggie and aluminum foil will add to it.

accuratemike · « **Reply #5 on:** January 23, 2007, 06:28:45 PM »

On this chart:

Looks like a max load for a 1.5" bore is 500grs. I would suspect 1 3/4" to go a bit more but the curve doesn't make sense at the top end. And that is a load for a projectile. Blanks being larger. And it is a weight chart, with more room needed, the coarser the grain size you go. What grain size is proper for 1 3/4" bore and what are the maximum blank and live loads? 1200 grains weight of cannon grade powder is a substantially larger chunk of powder to make room for. MIKE

Edit: I just checked and, the roughly 1x1 bore of my golfball Gribeauval's sub-chamber holds 307.2 grains weight of what my pyrotechnics buddy called cannon powder. It's not the large curd stuff I see the full scale guys shoot at the re-enactments. Probably more like F. It is well within the chart, heck, I would shoot lead with it. You never get an opportunity to see a golfball at max load. I need to see a chart of grain size, grain weight to volume of various grades of powder etc. . I'm sure it is here somewhere.

Edit Edit: Does this mean I am shooting a 1" bore cannon?
"Addendum For mortars and howitzers the the diameter of the powder chamber is the considered the bore diameter."

GGaskill · « **Reply #6 on:** January 23, 2007, 09:38:39 PM »

There must be a way, how were Mt. Howitzers loaded?

Mountain howitzers, being designed at the end of the muzzle loading era, were loaded with preassembled cartridges with a powder bag tied to a sabot banded to the shell. They were loaded as a single piece. The original chamber had an extremely tapered section between the full bore and the chamber; so shaped that I can't see how they would have had a problem loading the combined cartridge.

On a full scale Mountain Howitzer we are able to push a foil wrapped charge into the chamber with much trouble.

Is your bore/chamber shaped the same as a real one (is it a real one)? It looks like there shouldn't be a problem.

Anybody recommend a maximum charge with a projectile for a 1 3/4" gun? Which grade of powder?

In MY OPINION, the maximum charge for a shot in any bore is a square charge, that is, the length equals the diameter. Golf balls are an exception because of their extremely low sectional density but a heavy charge is going to launch them too far anyway. In a chambered bore, I would size the chamber for a shot load and deal with salutes secondarily. You can always put more powder in the bag and have it occupy the full bore section if you don't use a shot.

For a 1.75" bore gun firing golf balls or salutes, I would use Fg. For metallic shot, cannon grade.

Artilleryman · « **Reply #7 on:** January 24, 2007, 02:51:15 AM »

I meant to say "On a full scale Mountain Howizter we are able to push a foil wrapped charge into the chamber without much trouble."

firebuckeye · « **Reply #8 on:** January 24, 2007, 04:15:25 AM »

This is some great info. Anyone know how many grains of fg would 1.25 x 1.25 powder chamber be? I can measure but though maybe someone already new.

Don Krag · « **Reply #9 on:** January 24, 2007, 06:41:36 AM »

Same type question.....

For a 6" bore mortar...how do I go about designing the powder chamber? For the breech section, I have a 6" OD x 6" plug of 4140 steel. I was probably going to do 2" dia x 2" deep chamber. Given teh walls of the tube and the plug together, I could open this to 3" dia x 2" deep. Will this hold enough Powder to toss a 6" dia ball a few hundred yards? Is there a volume chart for powder charges somewhere? What are the typical sizes on the 5.5 Civil War pieces?

GGaskill · « **Reply #10 on:** January 24, 2007, 09:59:02 AM »

A 24 pounder Coehorn of the Civil War era would throw a 17 lb 24 pounder shell 1200 yards with 8 ounces of powder. The chamber dimensions are 3" at the top, 2" at the bottom with round corners, and 4.25" deep. There is a range chart in the back of the AOP folio for the Coehorn but it is at home.

I can't help with a bulk density for black powder; you need to measure a container and calculate its volume, then fill it with powder and weigh the powder and calculate the density. If your container volume is not easily calculated, weigh it empty, fill it with water and weigh it again, and calculate the volume from the density of water.

I can't really do more than guess how much powder you need from the info you have given. How heavy is the shot? What is your windage? You probably don't need more than 4 ounces but that is just a guess.

Artilleryman · « **Reply #11 on:** January 24, 2007, 10:32:37 AM »

Another piece of information would be how far do you want to shoot the projectile to? Not much point in throwing the mortar projectile further than you can see it land. We use a little over 1.5 oz of 1fg in a 24 pdr mortar for 100 yards. We use 4 oz of 1fg in an 8 inch siege mortar. This will throw a 45 lb shell just over 100 yards. Twenty ounces of 1fg will throw the shell 900 or more yards, depending on the weather and wind direction.

Don Krag · « **Reply #12 on:** January 24, 2007, 12:02:40 PM »

Hah...no need for 900 yrds! I was thinking 200 yrds for some of the motar competitions. I was guestimating 2-3 oz Fg for a 6" zinc ball to get me out 200-250 yds. I'll be getting 25 lbs of powder next week, so I can weigh out some loads and see how big of a chamber I can put them in. Does the shape of the chamber play a large role? ie...is a narrow deep chamber better/worse than a wide shallow...or does it make a noticeable difference?

Cat Whisperer · « **Reply #13 on:** January 24, 2007, 12:16:27 PM »

Good point Norm -

I have a mortar that will throw a 16-20-24oz soda-pop bottle (full of concrete) over a 1,000 yards. It is a major problem trying to find a range big enough. It is a real temptation to try to clear the mountain top behind the 100 yard range - National Forrest too.

Not a bad idea to plan to shoot in available spaces - which out West might be readily available.

Will Bison · « **Reply #14 on:** January 25, 2007, 10:32:36 AM »

Howdy all;

I have to agree with George Gaskill, a Square Load is a good starter charge. In a properly built gun it should be more than safe. This assumes the proper wall to chamber diameter ratio is maintained. In a mortar this may be too much in terms of range.

We have two safety issues, safe operating pressure at the instant of firing and control of the shot downrange. Both of these factors will determine a maximum charge.

Bill

Rickk · « **Reply #15 on:** January 25, 2007, 11:40:17 AM »

If you make the chamber way to big, and the realization that you don't have access to a 1200 yard range sinks in, you may find yourself reducing charges to the point where they are hard to manage and you get erratic ignition. After fighting with my mortar all summer to get good ignition for 100 yard shooting, I am thinking that GG's "square charge" concept has a lot of merit. My next mortar will have a subchamber alot closer to what I really need for 100 yard target shooting. If you are unsure, maybe make your guess a bit smaller in diameter than it is in length. That would allow you to open the chamber up a bit if needed and still be somewhat "square". Remember that volume is related to the square of the diameter, so if you open it up just a little, you get alot more volume.

somethign else to think about if you use foil charges... if it is much wider than it is long, it is hard sometimes to get it to go in straight. If is doesn't go in straight, ignition will be erratic.

accuratemike · « **Reply #16 on:** January 25, 2007, 12:51:37 PM »

Let's say we are talking about golfball howitzers here.

Quote from: firebuckeye on January 23, 2007, 02:25:37 PM

I was wondering if it is nessasary to have a powder chamber when building a howitzer? What is the purpose of it? And if you were building a golfball howitzer what would be the max powder chamber size? Also how does width and height come into play. For example would the design ever be 1.5 x 1, or should it be same both ways. Hopefully I explained what I am thinking.

And down range means we are shooting at a target and backdrop. And golfball bore is off the load chart. And how does this "Addendum For mortars and howitzers the the diameter of the powder chamber is the considered the bore diameter." fit in? Is the bore of the gun on the chart the bore of the chamber or bore of the gun? Thanks, MIKE

Artilleryman · « **Reply #17 on:** January 25, 2007, 01:24:18 PM »

The idea behind having a chamber in a howitzer was to have a strong breech area, yet a light overall barrel weight. This would allow for a relatively large bore cannon that was light enough to move around the battlefield easily. The limitations of the howitzer was that it was designed to throw shells and cannister, but not solid shot. Shells in a 12pdr field howitzer used no more than 1 pound of powder, and the 12 pdr field gun used 2.5 pounds of powder for solid and case shot.

So as to the addendum organizations such as the N-SSA limit powder charges and projectile weights to keep pressures down. In howitzers the charge is figured on the chamber size because there isn't as much metal around the breech.

So to answer your questions the powder charge is figured on the chamber size in howitzers not the bore size.

Hope this helps.

accuratemike · « **Reply #18 on:** January 25, 2007, 02:19:38 PM »

So, my howitzer is 4" dia at the breech and I can have a chamber roughly 1 5/16" bore. (Or 4/3=1.3333") And my gun is to be charged like it is a 1 5/16" bore. So, according to the chart, a little more than 300 grains for "live" fire and, a little more than 600 grains for "salutes", would be "safe" maximum loads. I'm also extrapolating that I could use a chamber with a smaller diameter than 1 5/16" and still safely use the maximum loads above. Now I need to find a density of F and Cannon powder so I can see how much volume I'll need for 300-600 grains weight. MIKE

Edit: I found a density for F, 235 grains/cu. in.. 600/235=2.55cu in. , or, a chamber 1 5/16" x 1.886" would hold an entire 600 grain (weight) blank load.

guardsgunner · « **Reply #19 on:** January 25, 2007, 02:36:53 PM »

Don, I takes 1640 gr. 1F to get my 24pdr. ( 5.8") to 250 yards. Wind may vary ; making for an adjustment up or down.
Around 1300 gr.1f for 200 yd.
For whatever reason modern BP. does not seem the same power as the Civil War period powder with charge requirement usualy being one step over the yardage given on fireing tables. Works about the same with both our 24 pdrs.

Don Krag · « **Reply #20 on:** January 26, 2007, 08:18:37 AM »

G.
What's your shot on that? Solid zinc, hollow steel...etc? Reading all the replies here as well as other threads, I'll shoot for a 3-4oz chamber.

Funny thing is, I figured this would be the last gun I'd get finished. Turns out, I'll have the breech section steel being shipped to me and I've already got a very large lathe lined up for the turning. I've even picked out and drawn up plans for the mount. I have it done mid-March hopefully.

Are there cannon/mortar shoots that don't have required time periods? For instance, most of what I've found always requires Civil War uniforms and 1843-1865 artillery pieces. I have seen a few that simply state pre-1865 and corresponding uniform, but they are obviously aimed at CW. All my pieces are ~1500 - 1600, although the mortar design looks pretty close to several CW styles aside from no green paint.

guardsgunner · « **Reply #21 on:** January 26, 2007, 08:33:35 AM »

I'm shootng 17 lb. 1oz. Hollow cast zink balls.

I dont think the AAA out east require uniforms to play..