.303 Lewis gun cartridge?


I picked this up at the last Calgary April gun show as a round for a Lewis gun.
At this point that’s all I know.



You are correct, .303 Rimless Ball Mk 1 for the Lewis Gun.


Thank you Simon for that quick response.

Now at least I know what it is .

It just started snowing here in Calgary -it’s spring time !




Learn to love it, as we have. We got it on Saturday and Sunday! I posted a photo of my front yard but it was censored.

Those cartridges seem to have a knack for neck splits. (Try saying that 3 times real fast). It looks like you got a good one.



That That That


That’s easy for you to say. (Get it??? “That” is easy to say.)

:>) :>) :>)

5, 4, 3, . . .



“I posted a photo of my front yard but it was censored.”

Next time just put a cartridge in the window first then take a photo !



Was not Lewis gun made for .303 Brit (rimmed) and 30-06 (rimmless)? The one you show is rimmless.



The Lewis cartridge is a fatter and longer case. The case is 62mm long and the base diameter is 12.8mm.

Maybe Armourer has a photo of one next to a .303 ?



This round measures .501 just above the extraction groove.
And .506 + across the rim.

Looking carefully there is two neck splits already unfortunately .



It should be pointed out that the .303 Lewis (certainly its popular name, perhaps its official one) was an experimental, not a service cartridge. Jack


So, it is a semi-rimmed experimental, am I right?



The Lewis cartridge is a fatter and longer case. The case is 62mm long and the base diameter is 12.8mm.

Maybe Armourer has a photo of one next to a .303 ?


Your wish etc etc ;)


It’s known as a Rimless Experimental…but is Semi Rimmed


It was designed to use the same bullets as standard .303 rifle ammo, and was also designed to the same length. This is why the bullet appears to be pushed into the case.


Falcon: The rim diameter is also the same, or essentially so. The intent was, I believe, to produce a more powerful cartridge that could work through the Lewis feed system, including the pan magazine, with minimal alteration. Changing basic cartridge dimensions in belt-fed MGs is potentially no great problem, but the pan limited both overall length and base measurement of the new cartridge. Jack


IIRC P14 rifles were also converted to this ctg.


IN 1918-19, the Brits experimented with the Lewis Gun Cartridge design, in order to improve performance.
Since they had both .303 and .30/06 design guns available, they (my assumption)wanted to combine the large capacity of a 30/06 length cartridge with a Rimless or “semi-Rimmed” design and greater case capacity, for the same Bullet weight ( 174 grains), which would make conversion of either 303 or 30/06 guns to the New cartridge an easy proposition. ( and also utilise both calibre of magazines ( if one is familiar with Lewis magazine’s intimate construction details, one will see the advantage in this.).

Anyway, the War ended, so all “experimental” work was also shelved, but not before a quantity of ammunition had been manufactured (using .303 Making & Cordite Filling Machinery)…and hence the neck splits in remaining surviving cases ( cases not “finished annealed” just like ordinary Cordite Mark VII cases)

The Correct cartridge designation is "Cartridge, Ball, .303 (Lewis) Mark I "

Some attempts were made in the 1930s to resurrect the design for "Streamlined " Target Rifle cartridges by Kynoch, but with little success over the standard .303 mark VII for Bisley-style competitions.

A " Might Have Been" cartridge…now consinged to the Scrap bin of Cartridge History.

Doc AV
AV Ballistics.


I beg to differ with you on a couple of points Doc.

I don’t think the .30-06 Lewis had much to do with it, as they were not in British service, although the advantages of a rimless or semi-rimmed round were obviously part of the rationale. The principal driver was a requirement for a cartidge with a better performance than the normal .303.

Although Land Service interest waned fairly quickly at the end of the war, the RAF continued to have a desire to replace the .303 and continued playing with the .303 Rimless through the 1920s and a few were even made in the 1930s. In addition to ball they also made AP around 1918/19 and later Tracer VIIG and Buckingham bullets were loaded.

Although the cases are headstamped with a “I”, the round was never awarded the title of Ball Mark I and was simply refered to as the .303 Rimless with the design number. See attached 1919 packet label.

The design certainly had an influence on the .303 Magnum of the 1930s, but that round had a conventional neck and was different in other ways. It actually enjoyed some success in Match Rifle competition. The most important result from the “streamlined” Kynoch bullets that were used in normal .303 cases was the data gathered that led eventually to the boat-tailed .303 Ball Mark VIIIz for Vickers guns, introduced in 1938.