I recently came across some interesting videos on Forgotten Weapons. It turns out the US Army's primary sniper scope issued in WW1 was a prism scope. Initially 6x, and later 5.2x. Other developments from the period included extended detachable fixed magazines on the 1903 Springfield rifles. Interesting as a lesson in history, and what is old is new again. The photo below from the auction with the scope and the extended magazine box was likely put together separately after the war though. The Army did use the prism scope extensively, and separately used the extended magazine for other applications.

The scope itself had hash tags to range the height of a soldier, and had brass plates listing the various hold-overs and windage corrections to make long range hits. The reticle ranging marks matched a soldiers height at 1000, 1500 and 2000 yards. It was considered a very unsuccessful optic at the time. I imagine this was largely because the scope, while it had some good ideas in it, was developed by an artillery sight manufacturer with a much different definition of "long range". The elevation adjustments of the scope began at 500 yards, and extended to 3000 yards. Even today, that is beyond optimistic, and completely at odds with typical trench warfare distances. The scope also had a very limited eye relief as well, which made if difficult to use effectively. Modern ACOGs still have a pretty short eye relief, so even a century later, scopes have this issue to one degree or another.

ETA: Inaccurate information corrected. It does not seem that these magazine fed rifles were much issued outside the Air Service, ie: they were not made for regular infantry use. They were charged with stripper clips, and the 25 round magazine was fixed. The scopes were widely issued, just not with the extended magazine.

M1903 Sniper Rifle with Warner & Swasey M1913 Musket Sight - Forgotten Weapons.  Ian goes into a lot of detail about the scope and how it worked. All the range marks and hold overs are engraved on brass plates on the body of the scope.
https://www.youtube.com/watch?v=dVPbSt88S3Y

Auction listing with good pictures of the overall rifle,scope, and mag. The scope and mag were developed for separate uses, and most likely not deployed like this. But it does show that the army had the know-how to add an extended box mag. 10 rounds would have been useful for this kind of set up, I think.
US SPRINGFIELD MODEL 1903 RIFLE WITH DETACHABLE 20 RND MAGAZINE AND WARNER & SWASEY COMPANY TELESCOPIC MUSKET SIGHT
https://www.morphyauctions.com/jamesdjulia/item/1249-386/

From a recent auction: a 1903 with extended magazine and prism scope from WW1


Scoped 1903 in WW1


another scoped 1903 in WW1


From a recent for sale posting - a view of the sight picture through the optic. The hash marks to the left of the crosshairs are equal to the typical height of a soldier at 1000, 1500 and 2000 yards (really?)


Range correction plate on the scope. Lots more explanation of the scope in the excellent Forgotten Weapons video.

Magazines for the 1903 were not ever issued nor fitted by the two Amorys. The experimental Air Service variant is really rare. Some people have retroactively tried to fit BAR magazines but usually they are trying to fake the Air Service rifle.

I  remember looking at this video a while back.

Wow I had no idea this existed.  Good post OP!