Nate, the "condition" and "originality" of any rifle can move it into the "don't shoot" category. Yours, because of the bolt alteration, should have the headspace checked by a gunsmith & perhaps for your comfort factor, test fired. He can then examine the fired brass case for any indicators of excess pressure. But as far as "quality" of engineering, materials & workmanship, there should be simply no worries.
The mainstream US factory ammo in 7x57 today is loaded down to accommodate the older less strong actions. Yours isn't in that "lower pressure required" category, but never hurts to go easy on these old gals. The barrel of yours is likely "Bohler" high pressure steel and entirely competent for its intended work!
Z1R rightly notes the possibility of a "standard" action size 7x57 chambering to have been utilized, particularly in special order context. Moreover, into WWII era years, "Intermediate" actions availability may have been compromised necessitating such as Mr Z's rifle. Your rifle, a child of the German Weimar Republic era, wasn't proximate to any such wartime circumstance. The precipitous cliffside Great European Depression didn't affect yours' quality!
And to all a good night...
John
