Armstrong 110pr Breech Loader-2

by John

Having commenced building a 1:10 scale model of this gun on a wooden carriage and traversing platform, I am also finding information about its history. First the build progress….

Glueing the traversing platform pieces. And a 4mm long series drill bit.

Gluing required some planning. The brass stops rebates were tricky to make last time because the platform was already fully assembled. So this time I made the rebates and installed the stops prior to gluing up.

Then there is the matter of the long, 4mm, holes across the multiple pieces of the platform, which is up to 152mm wide. Wood is not uniform like steel or aluminium, and deep drilling wood with small diameter drill bits usually leads to wandering crooked holes. So I measured and drilled each piece separately, prior to assembly. A tricky and exacting process. All except for the outside pieces shown being clamped above. They were drilled, one side at a time, after that side was glued, using the existing holes as a drill guide. I was happy with the results of the drilling and gluing.

Cutting out the carriage cheeks with a 6mm endmill. The workpiece is screwed to the sacrificial base piece with large woodscrews (not visible), then the required holes for the model are drilled through workpiece and sacrificial base and bolts are inserted. These bolts stop the workpiece from moving in the final stages of cutting the part free. The carriage cheeks will not be parallel in the final assembly, being narrower at the rear than the front, and the holes will need to be modified at that stage, so I have drilled them undersize at this time. Same goes for the trunnion cut outs.
Glued and drilled traversing platform (one of 2); laser cut 1mm stainless steel strips ready for attachment (AUD$55 including material. Probably saved me a day and more accurate than I would have managed), and CNC cut carriage cheeks, straight off the mill. Recycled Victorian Mountain Ash floor boards).

Not so much workshop time lately due to family factors, so I have been reading and searching references. And thinking about how to machine the barrel. Important to get the sequences right. And to have available the correct tools.

A is the screw which compresses the breech block E into the copper seals F and H, after the projectile and charge have been loaded through the breech. B is the weighted handle which operates the screw. C is the breech coil. D and J are further coils. K is the trunnion piece which was forged including the trunnions.

The originals were made using the Woolwich “coil” system, in which components of the barrel were made into various sized and shaped cylinders by winding white hot strips of iron or steel around a mandrel, then hammer welded into a single fused mass. The various cylinders were then accurately turned on large lathes into the final pieces which were heat shrunk together, and finally furnace welded. The Armstrong 110pr had 7 such major pieces. Only the innermost barrel cylinder was steel.

There were 2 barrel designs of the 110pr guns. The above diagram is the 72cwt version, which was 2″ shorter than the 82cwt version. The latter has more taper to the chase of the barrel, and will probably be the one which I model.

The 2 types of 110pr barrels. You can see my metric conversions of the dimensions. And a few dimensions scaled off the drawing. I think that I will make the 82cwt version.

I will not be making my model using the coil method, but I am probably going to make the trunnion ring with trunnions as a separate item, and shrink it onto the barrel, along the lines as described by Still thinking about those big asymmetric double start threads on the breech screw. I have a high tensile 32mm bolt and nut which I am considering using.

The scaled bore should be 17.78mm. I will approximate that to 18mm. Will need to extend a 17.7mm drill bit, and to make an 18mm D bit from silver steel. Jefenry welded an extension to an adjustable reamer to finish his bore. I will possibly use that technique also.