My brother in-law has an old rifle he brought over from Europe many years ago, on the barrel is marked 5.4mm must be a about 50 yearso old.
He mentioned the name but I don;t recall off hand, the rifle was used for military training, I assumed it was a .22 rifle.
Anyhow the converting 5.4 mm to incehes converts to .212, any idea if Europe has/had some caliber equivelet to a .22 that is a tad bit smaller? He indicated that a .22 long rifle chambers in the barrel but he did not feel safe trying to fire it. BTW .22 converts to 5.6 mm, he also noted that the bolt/firing pin is off center so these 5.4 mm rounds must be some sort of rim fire cartridges.
Anyone ever hear of a 5.4mm cartridge?

My brother in-law has an old rifle he brought over from Europe many years ago, on the barrel is marked 5.4mm must be a about 50 yearso old.
He mentioned the name but I don;t recall off hand, the rifle was used for military training, I assumed it was a .22 rifle.
Anyhow the converting 5.4 mm to incehes converts to .212, any idea if Europe has/had some caliber equivelet to a .22 that is a tad bit smaller? He indicated that a .22 long rifle chambers in the barrel but he did not feel safe trying to fire it. BTW .22 converts to 5.6 mm, he also noted that the bolt/firing pin is off center so these 5.4 mm rounds must be some sort of rim fire cartridges.
Anyone ever hear of a 5.4mm cartridge?

A 22 would be 5.56 or thereabouts. I think there was a German 5.4 cartridge but it's not the same as the 22 LR and I would not shoot it until learning more.

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No life story has happy end.

Pretty sure it's a .22 lr.

Since it is a European gun the numerical designation almost certainly refers to bore diameter, not groove diameter.

The .223 cartridge in its NATO form is 5.56mm. That converts to .218 which is the bore diameter, not the groove diameter, of the cartridge.

In Europe rounding and aproximating are extremely common in cartridge descriptions. An example, the 9.4mm Beaumont and 10mm Beaumont are the same cartridge. It uses a .386 bullet (which is 9.8mm) go figure.

The Soviet 5.45mm is roughly equivalent to the 5.56mm Nato. Don't get too nitpicky, a 5.4mm is some form of .22. Whether it is an exact metric equivalent of the .22 LR or not it is still a .22.

Here are some other examples from a site listing British, American and Metric cartridges. Note how decimal bullet diameter does not directly correlate to the metris designation. Is is tabular. hope it translates well. The first decimal figure after the cartridge description is bullet diameter.

5.4mm x22R Tesching C 0.220 0.865 0.400 0.245 - 0.340 - - -
5.45 X 18mm Soviet C 0.210 0.70 0.300 0.220 - 0.300 0.98 S-B 1970's
5.45 x 25mm Russian Auto C 0.224 0.708 0.298 0.242 - 0.298 - - -
5.56 x 30mm Mars C 0.223 1.20 0.374 0.250 - 0.374 - - -
5.5mm Velo Dog/5.75 Velodog B 0.225 1.12 0.308 0.248 - 0.253 1.35 S-B 1894
5.5mm Velo Dog/5.75 Velodog Short B 0.225 0.690 0.308 0.248 - 0.253 0.95 S-B 1894
5.6 x 17.5R Francotte Auto D 0.225 0.690 0.310 0.251 - 0.253 - - -
5.6mm Scheiben Pistol C 0.220 0.748 0.433 0.244 - 0.354 - S-B 1890's
5.7 x 33 Tesching
/5.5mm Soemmerda C 0.228 1.450 0.390 0.250 - 0.366 1.75 B -

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Gunsmithing since 1961

Any gunsmith of moderate competence should be able to make a cast of the chamber and determine more about what the rifle was meant to fire. Since it is of apparently unknown history and make, it might not be a bad idea to have a gunsmith look at it anyway before attempting to fire it.

It is most probably a 22 L. R.

Cartridge designations are often NOT exact.

Ex:
38/40 is more like 40 cal.
38 Spec is closer to 36 cal.
44 Mag is roughly 43 cal.
32 S&W is closer to 31 cal.

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Regards,
Lee Jarrett

The old German bore designations are indeed a little different! The 5,4mm is indeed the bore measurement ( the measurement taken between two opposing 'lands', whereas if the 'groove' measurement was taken it - should - measure 5,6mm. So the Germans took their measuements often between tha lands, where the Americans denoted their measuements taken between the grooves!

Most likely it is a .22 Long or .22 LfB (LR)

BUT to make sure: make a casting of your chamber. Measure it and make sure!

Greetings, Dafas