5.5" Gun vent tube (Primer) "RML" Headstamp

I recently acquired a vent tube for a British 5.5" Field Gun.

It is based on a .303 case but is cut off to 1.765" length to make a straight-sided case. It also has a brass strengthening insert held in at .50" from the case head by three stab crimps.

The headstamp is, at 12:00: MK.5.R.M L 56.

I am unsure as to exactly what these markings mean. Is “M L” one of the Australian factories?

Thanks for any info.

I just noticed this case in one of my drawers again earlier. Any ideas?

No, the factory code is “RML” but I don’t know who that is. I have the identical cartridge also.

I will see what I can find out.


RML or “R^L” ( Royal Laboratory, Woolwich)??? Most special primer cartridges or Ignition Cartridges were made by Woolwich both in peacetime and in War.

BY the Way, “RML” in Artillery terms refers to “Rifled Muzzle Loader” Guns, (Armstrong wire-bound types), using a lead skirted cast iron projectile, loaded from the Muzzle, over bagged BP or Gun Cotton…Most common RMLs were the “Disappearing Guns” usually used in Coastal Defence Batteries.). I would have thought that by the time the .303 case was developed, the RMLs were obsolete, and replaced by RBL ( Rifled Breech Loaders).

Doc AV
AV Ballistics.

It is definitely RML and not R/|\L.

With a date of 1956 it is also far too late for a Rifled Muzzle Loader.

These primers are also found headstamped: MK.5.RG.59


I have one with that headstamp as well.

This “Tube, Percussion, S.A. Cartridge, Mark V” also exist with MK.5.RML 52 headstamp. Same unknown code also exist in 20 mm H-S dummy cartridges from 1950. This may help to identify its manufacturer.

“RML”…RM Limited…Possible interpretation…would point to a Commercial company??? “R” Munitions Limited??
:Post-WW II?
Food for thought.

Doc AV

Possible, but I do not think it likely. The RML examples date from the mid fifties and apart from ICI Kynoch I cannot think of any commercial operation likely to have loaded them at that time.

Since neither I or anybody else has found any documentary evidence in the archives as to the origin of the code, we are of course guessing, but during that period several non standard manufacturer’s codes started to appear on SAA, particularly on 9mm Inspectors’ dummies. Examples are “RLB” for Royal Laboratory Birtley and “ROFB” for Royal Ordnance Bactory Blackburn. I just feel that RML is something similar.

The only clue I have found is that RML was at one time assigned to Royal Ordnance Factory Maltby, but Maltby was a rifle factory and I am not even sure that it was still in operation in 1956. However, it is a possibility.