Omega Bumper Automatic Calibers Reference Guide

I've always been fascinated by early Omega automatics -- the bumper or hammer automatics.

There were two sizes: 28.10 mm and 30.10 mm, and the movements lifespan extended through Omega's beginning to use calibre numbers in 1949 so there were initially sized-based designations, later calibre numbers.

This table shows how these movements were related and how they differed. I included photos of some of the movements I own, which range from pristine to far from it. Perhaps someone could use this as a reference . . .

Old Designation	30.10 mm subseconds	Calibre Number		Seconds	Date	Springs	Regulation	Chronometer
30.10 RA PC		330		subseconds	none	exposed	standard	no
30.10 RA PC AM JUB		331 see photo below		subseconds	none	exposed	standard	yes "Jubilee"
		332		subseconds	none	covered	standard	no
		333		subseconds	none	covered	"rg" fine regulation	Yes

Example of 331/30.10 RA PC JUB "Centenary"

Old Designation	28.10 mm subseconds	Calibre Number		Seconds	Date	Springs	Regulation	Chronometer
28.10 RA PC		340 see photo below		subseconds	none	exposed	standard	no
28.10 RA PC BULL		341		subseconds	none	exposed	standard	Yes
		342		subseconds	none	covered	standard	yes
		343 see photo below		subseconds	none	covered	"rg" fine regulation	Yes
		344 see photo below		subseconds	none	covered	swans neck regulation	Yes

28.10 RA PC





Calibre 343




Calibre 344

Old Designation	28.10 mm center seconds, no date	Calibre Number		Seconds	Date	Springs	Regulation	Chronometer
28.10 RA SC PC AM		350		center seconds	none	exposed	standard	no
		351 see photo below		center seconds	none	covered		Yes
		352 see photo below		center seconds	none	covered	"rg" fine regulation	Yes
		354 see photo below		center seconds	none	covered	swans neck regulation	Yes

Calibre 351






Calibre 352

Old Designation	28.10 mm center seconds with date	Calibre Number		Seconds	Date	Springs	Regulation	Chronometer
		353 see photo below		center seconds	none	covered	standard	no
		355		center seconds	none	covered	swans neck regulation	Yes

Calibre 353