lead nose or pure lead bullets give (or gave) feeding problems in semi-automatic pistols and even bolt action rifles. It has to do with the nose of the bullet sliding on the feed ramp. Some guns are more prone to troubles than others. Angle of the ramp, how much the ramp controlled the feed vrs the lips of the magazine and the smoothness of the ramp. The last was a common modification for Military surplus pistols, Polishing the feed ramp to get rid of machine marks (groves) to get non-military bullets to feed reliably. Not a big deal but the more hand work the more expensive a gun is to manufacture.
US Shotguns used, at first, commercial ammunition which in WW I days meant a "paper" shell body with a crimped on sheet brass rim and primer cup. It tended to absorb water and swell in trench (or jungle) conditions and was replaced by a full length brass case.
A standard load for the military was a buckshot load of 9 pellets of 00 size which is .33 caliber and 53.8 grains (just under 3.5 grams).
Nobody was using steel or iron shot in the early part of the last century. Even "plated" shot was rare and expensive.