303 Cartridge Case - Rim Design Change


Does anybody know when the design of the .303 case rim was changed to the squarer form rather than the earlier curved design?


Hmmm, interesting question. I’ve just read through Labbett & Meads ‘.303 inch’ where I would have expected to find the answer to your question but, unless I’ve missed it, there is no reference to this change.
I’ve also gone through my own collection noting the dates on those rounds with a square edged rim and those with a rounded edge but I really cannot see any reliable pattern and there appears to be a big overlap of dates. RichT has a more comprehensive collection of headstamps than I do so perhaps he can help with this.
I will also send an email to Roger Mundy here in the UK - if anybody will know the answer it’ll be Roger.


Jim - yes its interesting. One of those sort of questions just forgotten to be asked for all these years! The earliest UK mfr example I have is 1926 & this is ‘square’. Prior to that my collection starts again in 1918 where the examples I have are ‘curved’. I couldn’t find it in Labbett & Mead either nor any other publications. I also have a 1931 dated Canadian DAC example which is ‘curved’. Hopefully Richard & Roger may be able to expand on this.


Unfortunatly I am in the same boat as you two, I have a mixture of dates that overlap and no real cut off date to see in the dates. I was once told the date of the switch I think it could have been Roger. I have a really comprehensive list of significant dates in the life of the .303 but there is nothing on that list and like you I have been through all my books and pamphlets.

I will keep looking but here’s hoping for Roger :-)



The more I look the less convinced I am that there was a definite date for the design change. In my collection I have an Mk IV Ball ‘B IV C’ with a clearly defined square-edged rim but then I also have a Mk V Ball ‘R L C V’ with a rounded contour. Both rounds are undated but I think its safe to conclude that the Mk V was made after the Mk IV so their rim designs really should be the other way around.
Sorry if I’m confusing the issue…!


Yes - this is a bit confusing isn’t it!! I wonder if there might be something in the Ordnance board notes. Pending a reply from anybody else - I will check next time I am at the National Archives.


My impression has been that the rounded-off contour of the edge of the head in the .303 was intended to make feeding of the rimmed cartridge more reliable from a box magazine. The .30-40 Krag and the 7.62 m/m Russian rimmed also feature a notable bevel on the edge of the head for what I assume is the same reason. In the case of the .303 I would suggest it was at some point realized that it wasn’t really helpful in feeding and so was dropped. Why there’s no paperwork to address the change is a little bit of a mystery to me. Jack


There was a change in the shape of the .303" rim which was referred to as the “charger rim”, now all I have to do is find the reference to that!



Excellent. The plot thickens! :-)