copied and pasted from an article i found:
The MAS-45 (MAS standing for the French firearms manufacturing firm "Manucacture d'armes Saint-Étienne") is a .22LR, bolt action, magazine-fed rifle primarily used for training purposes. The gun itself is patterned after the Mauser Model 45, which itself is patterned after the KKW rifle, which was a trainer rifle that emulated the manual of arms for the Mauser 98 centerfire rifle. The KKW was used by the NSDAP (Nazis) in the pre-war years as a means for soldiers and paramilitary forces to practice their shooting skills in "shooting clubs", which in reality was simply to train men how to shoot for soldiery.
The Model 45 Mauser, and subsequently the MAS-45, emulates the controls of a Model 98 Mauser in that the safety works identically as a typical Mauser 98 rifle - left wing is fire, center position is safe with bolt unlocked, and right position is safe with bolt locked. The MAS-45 has peep sights mounted on the rear receiver bridge, whereas the KKW closely resembled the Kar 98K in resemblance and ergonomics, including the tangent sight. The MAS-45 sight is graduated from 30 meters to 150 meters. The MAS-45 is also magazine-fed, unlike the KKW, which was a single-shot, from a 5-round detachable magazine. The trigger is like a typical military surplus two stage trigger.
The stock on these guns are usually made of beechwood, as is on my rifle, and the metal was grey parkerized. Model 45s made by Mauser usually either have a nice rust blue finish or black parkerization, depending on when it was made.
About 50,000 MAS-45s were produced in France; initially the Model 45 was produced in Mauser Oberndorf for the French military, but later, the French took Mauser's machine tools - and their ability to produce Model 45s - over to Saint Etienne. Model 45 Mausers are typified with a "Mauser Banner" on the receiver ring and the buttplate, whereas the MAS-45 has the "MAS" logo on the respective parts. Navy Arms imported a lot of these guns sometime in the 1980s, and these guns can be found from time to time on Gunbroker. A very neat firearm for someone who enjoys shooting Mausers, but wants the inexpensive price-per-round (at least pre-Newtown) of .22LR.
a link to some nice pictures of the markings you are missing:
https://imgur.com/a/pXp9C
to me it seems yours is also missing the "step" at the front of the receiver, and a few other machining things, along with anywhere the rear sight would be milled or attached.
i couldn't find anything on a repro receiver, so it can be a special run made by someone, though i'd really think the chances are better of an unfinished one walking off the manufacturing line.
it's maybe even more possible it's a Norinco JW25A receiver, though doesn't have the dovetails in it - again may be unfinished receiver that walked off the manufacturing line.
thought it may have been a mauser 350 or 340, "patrone" but the shape is off from what you have
do some research on "Gustloff-Werke Waffenwerk Suhl KKW series" and /or Simson. these have no grooves like your receiver and the wider port, but most have that step toward the front.
finally, research kkwehrsportgewehr
you may actually have there is an ANSHUTZ - JGA OR Anschutz JGA Buscher-Sportmodell Trainer, maybe even a walther trainer
some interesting watching here
https://www.youtube.com/watch?v=5h3NnS8KBaE
i think your best chance for success of finding out really good specific info is on a mauser or k98, KKW, etc forum. and not limit yourself to thinking MAS 45. may also check into zastava, BRNO, and czech made firearms
it seems with the rush of prewar germany's war machine to get stuff done, and with a few of the replica / novelty / or seriously made clone .22lr mauser actioned rifles, it's like peeling an onion back. the lack of markings, the front step in the receiver, or grooves got me stumped, but am now more familiar with pre and post mauser 22lr's alonge with ERMA 22 conversion kits for 98's!
