Texasjack, I wouldn't shoot 2 3/4 (70mm) shells in this Gun! We have lots of these guns here in Germany and one of the first thing people learn in the prep course for the hunting license is NOT to put 70 mm shot shells into 65 mm chambers!!! It might be dangerous!!! One reason, why the ammunition makers came out with the 67,5 mm shells. These will work without problems! Of course it's POSSIBLE to shoot 70 mm but with lots of risk! As for the 7x57: it's very unlikely that it is NOT a 7x57R because this is a breech loading gun and the 7x57 (7mm Mauser) was especially modified to 7x57R for this Breechloaders!

Best,
Wolfgang

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