Starting first major mortar build

[jamesfrom180]

Well I happend into some nice steel tubing.  The bore diameter is 2.65", and thanks to Industrial Metal I was able to get a drop of 2.65" 1018.  When I recieved it it was 2.75" this will soon be corrected.  We will see how good the local lathe monkey is. 

So first up what ammo to use?
Coors light in the 12 FL.OZ can measures 2.48" to 2.51" Figure filled with concrete weight will be about a 1lb to 1.5lb so this is in my liking. 

Does my projectile meet my windage requirements?
2.6"/30 = 0.088333" 28x0.0883"= 2.47" Projectile should be 2.47" can is 2.48"
    Conclusion is that the can filled with concrete will be tight but since this is a mortar and contact will be limited to the short barrel this is acceptable. 

Ok what should my chamber dimensions be?
My billet is 2.65" when it comes back from the machine shop, hopefully.  2.65"/3 = 0.8833" So the bare minimum wall thickness should be 0.8833" To keep tooling down I choose 13/16" diameter (chamber diameter 0.8125") and by using the chart for maximum load for under 2" bores I find the load is 110 grains.  Boring a hole in a block of wood with a bit with a 135degree point I find that a hole 0.850" depth yields a chamber capable of holding 110 grain load of cannon powder.         
      Width 0.8125" depth 0.850"   Max load 110 gn Cannon grade Goex powder

Next what diameter trunion should I have?
I think I will go with 1" slightly larger than my chamber. 

Looking up in my black book I find that the interference fit for a hole of 2.5" (1.97" to 3.15" Class FN2 medium drive) would be +0.0019" to 0.0014" So my breach to barrel should be a "sweated" or press fit.  I plan on welding the breach in as well as channeling the breach and welding in the trunion.  This will provide me a strong breach and a design that should comply with most accepted design criteria.  I do plan on using a touch hole sleeve quite possibly a 3/16" bolt drilled for a touch hole. 

Please if you have followed this far feel free to add any critiques or point out any errors. 

I will add build photos and pen & paper drawings when I can. 

[armorer77]

How are you going to bore 2.75" to 2.65" ? My can bores are 2.690" for a Busch can at 2.625" . I use a 1" chamber and a 1.25" trunnion . Armorer77

[GGaskill]

I do plan on using a touch hole sleeve quite possibly a 3/16" bolt drilled for a touch hole.

Do you mean a 3/8" bolt?  Unless you are using really small fuse, 3/16" is too small.

[jamesfrom180]

Thank you guys

I will have it turned to 2.65"
And yes I plan on using 7/16" or close bolt.  I do plan on using a smaller fuse. 

The wall thickness is 0.35" on the tube. 

I was amazed to find that the can did have such a variance.  I guess the color changing ink required a different process or was chosen so that other can manufactures could not easily duplicate the production.  Who really knows but hey it fits my mortar. 

I do have some questions on the most appropriate way to construct the touch hole. 

[Double D]

Full correct dimensions for  beer/pop can mortar is in the references sticky.

A popcan mortar with proper windage needs a bore of 2.667.
A Diet Coke can is 2.6 inches in diameter.  (2.6/39)x40=2.667

[jamesfrom180]

Well back on the project, unemployed now for a few months.  Bored a relief for the trunion.

[jamesfrom180]

I'll get the chamber bored tomorrow. Might attempt to slip the two pieces together if I can find the dry ice. Fit is a tight 0.05" so it will be a challenge.

[Double D]

Will you get .050 (fifty thousandths) difference in expansion of hot metal and contraction of cold metal?  That seems like a lot.

[GGaskill]

The coefficient of expansion of steel is 6 millionths of an inch per inch of material per degree Fahrenheit.  Assuming your diameter is 2.65", you would get .0000159" per degree of temperature difference.  For .050" expansion, you would need .050 / .0000159 = 3144 °F which is obviously impossible.  Now for .005", you would need only 315° difference which is easily obtainable.  Maybe .050" is a typo; hope so.  :-)

[jamesfrom180]

Yes that was supposed to be 0.005" pieces are slowly coming together. Found work again so progress has slowed.