Your "cartridges seat on the shoulder in the spool magazine"?

When was your MS made? The later Schoenauer magazine has a retaining ring that is not present on earlier models such as my (1922 proofed) M1910. If I attempt to load spire points (or any other projectiles without enough 'meat' toward the forward end), the third round will jam.

This is as they are going in, and I have heard the very same from other M1910 owners. If the profile of the entire finished cartridge is not very close to that of DWM 531, they shift a bit and the 'nose' (or not enough nose) gets jacked into a void between magazine and stock. In order to use them, three cartridges of the proper profile must be loaded first, then two of the spires.

Hornady 3715 has been 'out of production' (not offered) for some years now (2009 or so) and has become quite scarce. Watch MidwayUSA for 'factory seconds' of .375 270 grain RN. I have purchased them and am almost entirely sure they're Hornady 3715.

For advice regarding 'cup and cast', ask member Sharps 4590. He is an afficianado of cast bullets. I've used them only in a .44 Mag. Ruger and in black powder applications.

Kuduae had written of the Barnes 30486 in response to a query of mine regarding lead free loading for the M1910. Where I live you can't shoot most critters with lead any more and there are some big, juicy, destructive feral hogs hereabouts. He uses them in restricted areas, as well. All cartridges I have fired through the ol' M1910 to date have been my handloads of 35 Whelen brass resized and loaded with RCBS dies, Hornady 3715, and IMR 4895. Grand Dad used DWM 531 'back in the day' (there were a few in the case).

I Purchased some of the Qual Cart 9.5X57 brass to go with the Midway 270grain RN's, but haven't loaded them yet (or anything for several years). I need to dig out my bench and put these things to use.

This photo from a previous post by Kuduae shows several Schoenauer magazines. Note that the 'retaining ring' starts with the M1924. The caption is his:

Left to right:
M1903 in 6.5x54 length oa 86.4mm width 26.0mm length of rotor 77.8mm
M1910 in 9.5x57 l 86.4mm w 28.6mm rotor 77.8mm
Her the cartridges are guided by the base and bullet nose.
M1924, the so-called "Sequoia model" in .30-06
length 92.9mm wide 28.2mm rotor 84.5mm
This model introduced a cartridge guide ring around the bullets, in front of case necks.
The lengthening of the mag box to the rear necessitated a different, new bolt stop, as the old one would hang out in the air if placed farther back on the receiver.
M1925 in 8x60S length 92.9mm wide 28.2mm rotor 84.5mm
from here on the guide ring is relocated to support the specific case shoulder.
All the post-war Mannlicher-Schoenauers have these long magazines, they only differ in the position of the guide ring and the shape of the much simplified rotors.
M1952 Magnum in 6.5x68 92.9mm wide 28.2 rotor 86.2mm