Cartridge Filler

[Evil Dog]

My current project is a "half scale" Napoleon.  It is a 2 1/4" bore barrel with a seamless liner from Hern Iron Works... 37" long weighing right at 150 pounds.  That size ball cast from wheelweight weighs about 2 1/2 pounds.  The powder charge will probably never exceed 375gr of Fg... won't know that though until I start working up a load for it.

The main problem is the volume of powder is really pretty small in relation to the diameter of the bore.  A standard foil wrapped powder cartridge probably be less than 3/4" in length (that is just a guess, I haven't actually made up any yet).  I would prefer the powder cartridge to be atleast bore diameter as that should make it a lot easier to keep it aligned with the bore when inserting it.

Seems to me I remember a thread on this board concerning using fiberglass insulation as a filler but can't seem to find it.  When making up powder cartridges for my 1 3/4" bore Coehorn I use cornmeal to adjust the length of the cartridge to fill the powder chamber.  Would be an awful lot of cornmeal to make up a cannon cartridge though.

Any of you use a filler in your cannon cartridges for this purpose?  If so, what do you use and how well does it work?

Would appreciate your thoughts.

[Will Bison]

My first question is why such a light charge? It would seem to me that 375 grs would not impart much velocity to a ball of that size.

I have used Cream of Wheat as a filler in small arms. The cost is minimal when compared to the cost of the powder.

Just a thought, why not use a zinc ball? Zinc is very cheap and readily available. My own rule of thumb is to switch from lead to zinc at the 2 inch bore size.

Sounds like an interesting project you have going.

[Double D]

Will Bison, how about a tutorial on casting Zinc.  Where to you get it what do you need to cast, etc.

[Evil Dog]

Yes Bison..... would be most interested in finding out about casting zinc.  Double D.... what does your reference show as max charge for a 2 1/4" bore, 37" barrel?

[Will Bison]

Hi gang;

Here's a neat online utility to compute the weight of a round lead ball.  http://www.beartoothbullets.com/rescources/calculators/php/roundball.htm  Lead has a density of 11.350 and zinc is 7.133. So compute the weight of a pure lead ball of the desired diameter and divide by 11.35, that gives the weight in water. Now multiply by 7.133 to convert to zinc. Rounding off a bit, a 2.5 lb lead ball would weigh 1.6 lbs if cast from the same mould in zinc. Zinc is about like iron in hardness and weight (OK purists, it's close enough for government work) but is more malleable.

Lead melts at 327.5 C and zinc melts at 419.6 C so it takes a bit more heat to melt zinc. Zinc has a wonderful casting property, much better than lead. I don't use any aluminum equipment with zinc, the mould, dipper and pot are all of iron/steel. The melting point of aluminum and zinc are too close.

http://www.graybeardoutdoors.com/phpbb2/album_pic.php?pic_id=302

The mould above casts both lead and zinc. I had my machinist make several of these in various sizes. The basics are not much different than casting with lead other than the higher temperature. Notice that the mould has no protrusions such as a sprue cutter, hinges or anything the zinc can grab. As I said it is hard and once it hardens it ain't like lead. When lead hardens you can generally pry it off with pliers, forget it with zinc.

The normal hazard notes apply; toxic vapors, bad burns, no water and molten zinc poured or spilled on wood will almost explode. I don't flux zinc, just skim off the dross.

Availability: The US penny is made of zinc and most average households probably contain several hundred pounds of zinc. In its pure form (not copper plated like the penny) it is bright silver in color when first cast but oxidizes a nasty blackish color in a short time. I get it at the local scrap yard. It's commonly called "pot metal". Older cap pistols were always made of zinc. Many auto parts, tool housings etc are zinc. It is almost always encountered as die cast parts. Zinc resembles cast aluminum but is generally plated because of the nasty oxidation.

I started playing with zinc as an alternative to jacketed bullets in rifles. Worked great AFTER I figured out some of the little pitfalls. I began experimenting with it about 1963-1964. Great stuff for cannonballs due to the lighter weight and low cost.

[CrufflerSteve]

Will,

Thanks for the info. I have been considering trying zinc for some of the qualities you mentioned. I hadn't heard that it was pot metal. That will make hunting easier.

I have heard that zinc shrinks quite a bit after casting, more than lead. Is this true? I'd like to know more before springing for a mold.

Steve

[Will Bison]

Good point Steve. I know I have a chart or table that gives the shrinkage for various metals. Hmmm Which pile of books and papers is it in?

Let me look around here, might take me a day or so. As I recall it was not so different from lead that I was concerned about it and I do use the same moulds for both.

Let me do some research and I'll start a new topic so the rest of the folks can benefit.

[Cat Whisperer]

We tried sand casting zinc 4.5" diameter cannon balls.  Not very successful - shrinkage caused many voids.  Suggest a mould that can be pre-heated and also pressure casting.

[Double D]

E.D.

Sorry I missed this earlier.

The rule of thumb for powder charges over 2 inches is 2 oz of powder per inch of bore, Maximum. To avoid unsafe pressures the N-SSA adds another factor, mzximum projectile weight.  your 2.25 bore gun should shoot a 2.2 in. projectile  (minus 1/40th for windage)

So based on the N-SSA chart, 2.2 inch smooth bore would be 4.4 oz of Cannon grade GOEX and a  21 ounce projectile maximum.  If you use a lead ball projectile 2.2 in. diameter it will weight 36.7oz.  (Thanks Will for the link)

If you use 4.4 oz of powder you are going have a significant overload.

Reduce significantly for lead, or start collecting pot metal.

CW, where do we want to put that link Will has provided?

[Will Bison]

Well I found some shinkage info on zinc, not what I was looking for but it'll do. Expect about .008" per inch, so a two inch ball will shrink about .016". In my opinion that's reasonable. I miked some of my cannon balls and the above "rule of thumb" seems to be close.

I'll be having dinner later today with a friend who owns a foundry and I'll query him on some additional casting info.

Evil Dog; I fully concur with the NSSA powder charges. The ratio of charge is more dependent on the Sectional Density of the ball. The object with cannons is to get the ball from the muzzle to the target and print a good group. A ball going 500 - 700 fps is plenty fast.

Happy Thanksgiving to all.

[Will Bison]

I talked with my foundry operator friend after dinner on Turkey Day. He reiterated the requirement for good ventilation when casting zinc. He told me he has never used it in sand moulds. It defeats the purpose which is precision cast parts. Everything he does is cast from steel moulds.

I asked about the shrinking aspect. Suffice to say it turned into a looooong conversation. In a nutshell the mould expands when brought up to casting temp and then the zinc shrinks after that. The math got a bit confusing at that point. He said cut the mould to the desired diameter and live with it. With 1/40 th windage, a few thousands of an inch plus or minus won't matter much.

I have three custom moulds as pictured in the link provided above. They are 1 7/8, 2 3/16 and 2 15/16 in size. Total cost was $225 USD for the three. Not too bad considering what one pays for a Lyman mould these days.