Union base size for a coehorn

[rusty barrels]

I think this has been discussed before but I couldn't find it but what is the correct size for a union base. I have a hern 24# that supposed to be a (full scale) repiica but I doubt it, maybe a 12 but not a 24, its only 14" long and approx. 7" in dia. I've also heard that the north never had 12# but the south did. So based on the dimensions of the tube what size union base should I build?

[Rickk]

I built my Hern with their plans, which is probably a full sized base. It is 31x15x9 . It stays put, which is nice. To be perfectly honest, that size base works well with Hern's tube.

Hern's barrel is somewhat smaller than full scale, but no where near half scale

[CU_Cannon]

The Hern barrels are about 85% full scale based on their length.  In my opinion the full size bed is a little big for the Hern barrels.  It has a tendency of making the barrel look small. 

Here is my 12pdr next to a Hern barrel. 

[rusty barrels]

Thanks for the replies Rickk and Cu. Cu is that a illusion or is the herns bore off center? Thanks for the picture of comparison, that really helps.

[powder2burn]

When I made my mortar base for my 24pdr. Hern, which is slightly smaller than full scale, I used an untreated oak landscaping timber. I don't have the exact measurements here at home, but it was either a 6x6" or 7x6" or 8x8" any of those would work. They will be a  little lower and a little narrower than a full size bed, but you can make the length anything you want.  All I did was to decide on length based on how it looked in proportion to the mortar size and bolted the two pieces together, and went on from there.

CU-Cannon, what size bed is the Hern setting on and what is the size of the 12pdr. bed., Did you make the 12 pdr., I need plans for one.

FRED......................................

[CU_Cannon]

The bore is centered as far as I can remember.  I think it is an illusion from the camera and the paint job. 

The Hern barrel is on a full size bed.  According to the ordinance drawings the bed should measure 31”x15”x9”.  I think the one was pretty close to that. 

I did build my mortar.  The thread is here. It was scaled from the full size 24pdr drawings.  It was quite a project.  I did everything on a manual lathe.  If it was done on a cnc one it wouldn’t take much time at all.

I still have some work I would like to do it.  I want to put a lock of some sort so I can use musket primers.  I also still need to do some grinding to smooth out the bore a little.