mortar trunnions

[freddo]

A pal of mine has asked me to make a timber base for a brass mortar that he has purchased.I know little about mortars so I have studied all the material on the subject that I can find on this forum.The thing that puzzles me about his mortar is the shape of the trunnions.They are not round.They are round on the bottom but flat on the top. ie U shaped I can't see how they can be located in a groove,secured by the caps, and still rotate.The mortar is cast brass so one would assume that the shape is the finished shape intended.The mortar is designed and cast to a fairly high standard.
 Is there some other way of mounting mortars like this on a base?

[GGaskill]

While a flat top trunnion seems kind of odd, the typical block mount was not arranged for the angle of the tube to be rotated for range changes.  Instead, the powder charge was reduced to get a shorter range.

[Rickk]

freddo, got a picture of it?

[Artilleryman]

That flat shoulder on top of the trunnion is used to set your 45 degree angle.  The leading face fits into a notch in the block mount.  The caps fit outside of this part.

[A.Roads]

Hi Freddo,

British trunnions are round. Though I don't recall ever seeing one a flat top trunnion actually does make sense, as they pivot very little, often not at all - relying on a fixed angle ~43 degrees~ and varying the powder charge for range adjustment. What type of mortar is it a replica of? (assuming its not an original). 

Adrian. 

[Double D]

Also keep in mind some mortars had no trunnion caps and others had flat cap bars just to keep the mortar from jumping out of its bed.

[freddo]

Thank you gentlemen I get the idea What is the optimum angle at which to set the tube?
 Unfortunately I don't have a camera which is a bit of a bugger since it seems to be an essential for such discussions.I must do something about this
 As for the mortar I can only tell you that it seems to be a Coehorn type I shall get back to you about this when I actually start on the base

[Rickk]

If it looks like the picture that is in my mind the flat part will help fix the barrel at whatever angle (45 degrees?) you decide to set it to.

Any idea who the manufacturer of the barrel is?

[CU_Cannon]

Coehorn mortars are set at 45 deg.  In a world without drag this angle will give maximum range.  Since most of us will never go to the moon to try this out we have air to deal with.  I believe optimal angle for a sphere with drag is 33.5 deg.  This is still an idealization.  In the real world there is wind, humidity, high pressure systems and so on.  45 would be a good place to start.