7.62x54R Head design


#1

G’day all, long time no post.

Just a random question, does anyone know why 7.62x54R has the bevelled edge around the rim of the case?

Nick


#2

You are right, there is a 20 degree bevel, it seems to have something to do with feeding, but there are rimmed cartridges without bevel.


#3

Vlad-I wonder if it is so that if the round was loaded into the mag wrong (with the rim of the first round behind the second e.g _-), it would allow the round to ride over the rim? Just a thought that your post triggered.


#4

I was told that this bevel is due to the fact that M1891 rifle has a recessed bolt face.
Over prolonged use, dirt and grit will eventually be collected around the edges of the recess, and, without the bevelled rims, this dirt will cause problems on closing the bolt. The bevel allows some dirt to be present on the bolt face without posing problems.

just my .02 roubles on the subject ;)


#5

Why the bevel? because all the similar cases of the time ( 1880s) had a bevel, whether for use with Concave Bolt faces (like the Kropatschek) for feeding orientation in Mannlicher clips ( the Austrian 8mm cases); the special Mauser “A” base, also for both primer seal criteria and for headspace considerations, and so on. The .303 British was the First Rimmed case of the period with a Flat base and very little rim bevel ( more “rounded”, and it originally was fed from a straight column mag( MLM); The .303 later had a more pronounced “rounding” once the Cartridge was used with 5 round chargers and with a 10 round, double column mag, and specific orientation in the charger to prevent “rim-over-rim” jams.
Remember also that this was the transition period from single shot firearms to magazine fed, and that many of the former single shot cartridges were “transformed” into Cartridges for magazine weapons.( by tube loading, by
Box or Packet Magzines, etc.

A very interesting question, which answer is probably multiple in origin…
regards,
Doc AV
AV Ballistics.