The Chinese could have made a modernized version of the ppsh41 or ppsh43 and than later being found in the hands of the communist resistance in the USA.
My question for all gun nuts here, what is in general considered the best rifle of these, the kar98k, mosin-nagant, springfield or the endfield?
That's a sticky question, as they are all fine designs. First things first, though: the M1903 is basically the same design as the Mauser. So much so they had patent issues and had to pay royalties to Mauser. The bolt action ([censored] on open), the extractor, the number and position of locking lugs, etc.. make these essentially the same rifle when discussing which one's better. I'll try to break it down for you:
1. Mauser. The greatest majority of modern bolt action hunting rifles are based at least in some part on the Mauser [censored] on open bolt design with the large claw extractor and Mauser's magazine design. If you're going by how many successful rifles copycatted the Mauser design, then it's the best.
2. Lee-Enfield. James Paris Lee, and american of Scot descent designed a magazine system that the Royal armory at Enfield adopted with their successful Lee-Metford. One of the main features of the Enfield design was that opposed to most of the other bolt actions out there, it was a [censored] on close design. This enables a slightly faster cocking cycle. Couple this with the superior magazine that Lee designed, which held twice the rounds that others of the time did, and you had a weapon that could provide superior sustained rates of fire. If this is what you feel is important, then the Enfield is the best.
3. Mosin-Nagant. This bolt design goes back, IIRC to the Chaffee-Reese rifle. Mosin, a Russian officer designed the rifle with element of Belgium designer Nagant's included. This bolt design was very streamlined with less parts than the other two rifles. Disassembly was easier. So true to Russian/Soviet design philosophy, it's a pretty rugged rifle that is easy to learn and maintain. It uses a magazine much like the Mannlicher style, and in general the craftsmanship on the rifles was less than that of their counterparts in Germany and England. This does not make it a bad rifle, and if low cost and ease of manufacture, maintnenance and trainging are important to you, then the Mosin is the best.
Of all the rifles of that period, none of them are what I believe is the best rifle. To me, that would be the M1917, an Enfield design that American factories produced in WWI when Springfield could not make enough rifles for the demand. There were twice as many M917's in the hands of American soldiers in Europe during WWI than Springfields. This design was intended to replace the Lee-Enfield, with a more Mauser like design, but some improvements. The bolt half-cocked on open and fully cocked on close, so it's action was almost as smooth as the Enfield, and with the more robust locking lugs and extractor of the Mauser style it was an improvement over the Enfield. The only drawback, as I see it was the lack of a windage adjustable rear sight. The war came too quickly for the Enfield armory to tool up, so they kept the Lee-Enfield and the rest you know. The two american factories that had already received the tooling to make the rifles on contract offered the rifle, rechambered from the British .303 to the American .30-06 (which allowed it to hold one more round in the mag, since .30-06 aren't rimmed like .303) to the American government to ease the shortage of M1903s. So the rifle you thought the US fought WWI with, was in fact the wrong rifle. The Marines only used M1903s, but the Army mainly used M1917s.
Edit: The censored words are in fact not something that should be censored in this case. Please insert the word spelled c-o-c-k where the [ censored ] tags are. That would be as in "When you open the bolt on a Mauser, it c-o-c-k-s the action."
-Gunny out.