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35mm Oerlikon Cases

P

peregrinvs

Well-Known Member
Hi,

A friend gave these 35mm Oerlikon cases to my sons as a present. Can someone confirm my reading of the headstamps is correct?

BM = BMARC (British Manufacture and Research Company)
OE = Oerlikon
84 = 1984
181 = batch number

Also curious to know what specific gun they were fired from as the scorch marks down the side are interesting. Am I right in thinking some of the propellant gas is vented down grooves inside the breach to aid ejection?

Thanks,
Mark
IMG_3463.JPGIMG_3462.jpg
 
Thanks.

Following a spot of googling, would I be right in thinking these were made for use with the ex-Argentine Oerlikon GDF guns captured in the Falklands?
 
peregrinvs said:
Thanks.

Following a spot of googling, would I be right in thinking these were made for use with the ex-Argentine Oerlikon GDF guns captured in the Falklands?
Click to expand...

Yes. A batch of these guns was issued to the RAF Regiment for the defence of air bases, so BMARCo cases are not that uncommon in the UK. They used them for several years, but I don't know when they stopped, or what happened to the guns afterwards.
 
Does anyone have pictured of the 35mm fluted barrel? Specifically the part that puts those burn marks on the casings? Always heard of it but never seen a picture. Cant find anything online either.
 
From what little I've read it seems some guns experience fired cartridge case extraction problems, caused by adhesion of the cartridge case to the chamber wall. This can be resolved by fluting the chamber so when the cartridge is fired the propellant gases cause a pressure build up in the flutes surrounding the outside of the cartridge case. This causes the cartridge case wall to be pushed away from the chamber wall negating the adhesion to the chamber wall and allowing easier extraction of the fired cartridge case.
 
Last edited:
bdgreen explained it well. Downside to this feature is the resulting crud build-up in the receiver. Nothing a little Hoppes #9 won't fix.
 
In addition to what has been said, consider that the cases are steel instead of brass. Normally brass cases expand in the chamber to seal the gas, and then shrink when they cool, allowing them to extract easily. The steel cases don't expand and contract at the same rate as the brass, so the fluted chamber aids in extracting the cases.
 
IIRC fluted chambers were developed about a century ago in Italy, for a machine gun. They are mainly used when the primary extraction is weak - i.e. in blowback or hybrid mechanisms in which the fired cases are not pulled forcibly out of the chamber by an extractor, but rely on gas pressure to blow them out.

An alternative approach to prevent the cases sticking in such guns is to lubricate the cartridges; the oil or wax turns to vapour on firing. Sometimes this is achieved by a hard wax coating applied in the factory, but some guns have had an oiling mechanism over the breech, to send a squirt of oil into the chamber before each round is chambered.

There was another variation tried in which the chamber was smooth but the cartridge cases were fluted, but this was never adopted AFAIK.
 
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