Proper insert size for each raw in canister shells

[oldfella]

 

Hello, I have been reading posts on this forum for a while and found answers to pretty much every question I had but this is my very first post.

 

I was wondering if there is some sort of rule or even a geometric formula to establish the insert size given insert number by row and shell size.

 

For instance, say I am building a 5" shell (so the inside diameter of the shell case should be 4,5 inches) and I want to fit 5 cylindrical inserts, what should be the diameter for these inserts?

The same "problem" for a 6" and 5 or 6 inserts?

 

Of course there is trial and error and cardboard spacers to consolidate, some will just have enough experience to know what to do but in my case I am just starting to make bigger shells, I'd really like to get them right from the beginning.

 

As I said this is my first post on this forum but I'm not used to write on forums in generalbso please excuse me if I missed something, if this is the wrong section or if I sounded impolite in any way

[Carbon796]

Nominal 2" inserts, built on a 1-3/4" former. Spiked and pasted. Fit 4 to a nominal 5", 6 to a 6", and 9 to a 8" shell. 1-1/4" pupadelles, are supposed to fit. 7 to a ring in 5's, but I can only ever get 6. Without fiddling with the insert former size, and/or the case former size.

 

There are charts in PT.#12 that list insert and comet fits, for nominal shell sizes up to 12". And, the reverse, nominal insert and comet fits. To a proposed case ID size.

 

I can look up 5 to a 5" in a little bit when I get home from work. Mumbles also has a calculator for this, somewhere on the site I believe.

 

Edit, 5 in a 5" insert OD 1.666" or 1-21/32"

 

5 in a 6" insert OD 2.036" or 2-1/32"

Edited January 26, 2021 by Carbon796

[Mumbles]

I'm sure it's somewhere else too, but it was faster to just reattach than track it down. All you need to do is change the Shell ID and number of inserts, and it should do the rest. I included some reference information such as common shell ID's, and an approximation of the cannule or cavity in the center of the shell. It will also calculate insert sized based on concentric rings. The math was easy, so I included it.

 

There is a mathematical formula, but since I wrote this little calculator I got rusty and it'd take me a while to remember how it works well enough to explain. There's an article in a PGI bulletin about it, which is where I got the information from initially.

ID.xlsx

[Arthur]

Sometimes there are no rules! You could emulate a design you admire or design something totally your own. Sometimes I take a piece of scrap card ( cereal box?) and draw things out. Even so it's partly guess work and partly your own design. Look through the tins at the supermarket! buy the food that has cans that make good shell building tooling! Look through all the possible spiking strings they will all be slightly different in size and twist and may help in packing inserts firmly. Remember that a steel dowel is size +- .001 but a wooden dowel is much undersize

[a_bab]

A nice calculator I use: https://www.engineeringtoolbox.com/smaller-circles-in-larger-circle-d_1849.html

[oldfella]

Thanks for all your answers, in particular Mumbles xls document is what I was looking for and a lot more; looking at the formulas really makes me feel a bit ignorant...

 

I also have a couple of other questions: one is about a prime formula and the other is about the production of black match but probably I should start a thread for each one of them, am I right?

[Carbon796]

My personal favorite is First Fire prime, for hot. Followed by a scratch mixed BP prime. Compatible with anything you want to use it on, and works.

 

Commercial BM works for me, and I'm too lazy to make it.