My experience is with the 9.5X57, but your assumption is correct.

The early Schönauer magazine was milled with the profile of the proprietary MS cartridge for which the arm is chambered. With the M1924 ('High Velocity') a 'ring' was added to the magazine that held cartridges in place, but in the 'classic' M1903, M1905, M1908, M1910 the cartridges were guided by their closely matched shape from the shoulder to the nose as the cartridge lays against the follower (spool).

The first photo below (I believe I 'swiped' it from a post of Kuduae's) shows Schoenauer magazines from small to tall. The second image shows an M1903 (6.5X54) alongside an M1910 (9.5X57). The third shows 6.5X54 cartridges 'nested' in the magazine. You can see how the 'profile' of the cartridge matches that of the magazine follower.

That said, with proper fitting cartridges, the Schoenauer magazine and the MS overall deserves its reputation as possibly the smoothest feeding sporting arm ever devised.

The surest way to have cartridges that will feed smoothly in the Schönauer magazine is to build them precisely as the originals. Spitzer type projectiles, unless they are carefully fitted, will jam on the third round. It seems the most critical point of contact (or lack thereof) is about 2/3 of the way from the cannelure to the bullet tip. If your projectile is too narrow at this point it will fall into a void and jam. Kuduae has posted specific instructions for loading spires in the M1910.

Make them like these, they'll work smother than greased snot.

Here's an Eley blueprint of the 6.5X54

You'll also want to pick up some Mauser clips (if you don't already have them).

By the way, you're going to love these things! There's nothing like a 'prewar' Mannlicher Schönauer.