Hi Gary, I've been scanning through the 1915 Treatise and 1926 text book this weekend and read that for some shell and mortars, for ease of manufacture, the shell or mortar body was made of a dimension just under the bore width, while the rest of the body, being of a lesser diameter, did not have to be so finely machined. This made the manufacturing process simpler and therefore cheaper. It was also done for better centring of the shell or mortar in the weapon and a bonus was that there would be less wear in the barrel or tube, thereby extending the life of the barrel or tube. That said, the raised bands on your bomb are relatively close together. My DWS notes on ammunition, Issue 15 Section 1 printed 10/42 says this:
`The bomb body is streamlined and made with one or two guide bands which act as gas checks, and together with the vanes of the tail unit centralise the bomb when dropped into the mortar. The body may be of the following forms:
Mk II - Cast iron, two guide bands.
Mk III - Ford 7 steel or malleable C.1, stamped F.7 or M.C.1, as appropriate. This mark has a single guide band.
Mk IV - Cast iron with a single guide band.
The body is sand blasted and the nose and guide rings machined to reduce frictional drag. With the exception of the guide rings the body surface is varnished.
Some designs are fitted with a steel exploder container which is screwed internally to take the fuze. Later designs use a paper tube in lieu of the exploder container and are fitted with a nose adapter, screwed internally to take the fuze. The nose adapter, No I Mk I, may be of steel, zinc alloy or Ledloy steel for which the corresponding stampings are S, Z or L.B., respectively.'
The only diagram of an HE bomb is that of a Mk III, with one guide band. If yours is an HE bomb then it is no later than a Mk II. Unfortunately my DWS notes give no information about a Mk I HE bomb. The pamphlet details seven different design drawing numbers but confusingly does not detail which Marks of bomb relate to which drawing number. The table also gives the DA Fuze number associated with each design. Fuzes then in use were No 138, 150, 152 and 152A.
The pamphlet goes on to detail the smoke versions:
`Bomb M.L. Smoke 3-inch Mortar, 10 lb. This phosphorous-filled bomb exists in several Marks differing in the structure of the body.
Mark I - Similar to the Mark II HE bomb; side charging hole; double guide band.
Mark II - Cast iron; no side charging hole plug; single guide band.
Mark III - Steel, but otherwise as for Mark II.
Mark IV - Cast iron; nose container and body welded together.
Mark VII - Exploder container as an integral part of the head; single guide band; base charging hole.'
Again the pamphlet details six different design drawing numbers in a table, together with their fillings and associated fuzes. However one of the diagrams is to a seventh design drawing number. Fuzes available for use with the white phosphorous bombs were the No 138, 139, 150, 152 and 152A.
The Smoke observing, Star, Chemical and Practice bombs also all appear to have had two guide bands.
Nowhere in the pamphlet is there any mention or diagram of a cut-out in the tail, as yours has.
