vangulil,
Check for 67.5mm Brenneke slugs. I have 16 ga Brennekes that I brought back in 1982, and are 67.5mm. They were specifically intended to be useable in both chamber lengths, and so stated on the box. In the case of 12 ga.,I believe the "short" chamber was actually longer than 2 1/2 ". Your problem may be one of misunderstanding. The recent influx of 16 ga. 2 1/2" 65mm shells resulted from specific requests from American users of German guns, not because 67 1/2mm shells weren't useable. If you can find 67 1/2 mm, you might want to give them a try.
Mike
