Very nice photographs, looks like a very nice and original rifle. The stock has the right acceptance, but the wrist acceptance is key to authenticate (I am sure it is fine though, the wrist is more stable than any other acceptance, should be Crown/Y); also the right receiver acceptance would be helpful, as would be the bolts acceptance (under the bolt handle, opposite the bolt serial)
Regarding the Trench magazine, first impression is good, but detailed photographs are the only way to authenticate. Generally holding an original vs. a reproduction it is easy to tell.
That is a beautiful rifle, super nice and pretty hard to find this nice and original. Walnut stocks are quite possible for DWM until very late in 1916, really till the end. Even a couple are known for 1917, but rarely. It fits perfectly in every way (acceptance) for this range, - thanks for the extra effort with the excellent pictures.
Regarding the trench magazine, I can't say that it is bad, but it has several things that are inconsistent with known magazines and I would be highly suspicious of it. The chain style is not typical with the few types known, the follower is not the normal type (though this general style is known, but less common and yours looks a little more like the normal rifle follower). Also the markings that one would expect are lacking, - worst of all and the real issue is the structure of the metal looks lighter and probably blued which is wrong for an original. Your pictures are first rate though, so new ones probably wouldn't help, the chain being covered by canvas hides the chain, so its a little hard to see but I am pretty sure not right... typically these with the DRP marking are frauds, but I thought it possibly ok, but that might have been more due to my interest in that wonderful rifle and the nice touch with the canvas on the chain. Anyway, I doubt it is right, but am not going to discount it with these pictures. There are a few angles that I would like to have seen to compare with others, but if someone who was considering buying, I would recommend passing on the mag. Way too likely it's bad. Mike might have different views, he is pretty sharp on rifles and accessories, but the more I look at it (and compare) the less I like it.
That's a nice gewehr 98 as Paul stated. Unfortunately, imho, the extended mag is a repro. I've got three originals & have handled a few others & a couple of repros, so that's what I'm basing my opinion on.
Thanks for posting your rifle, looks like a possible re-barrel as I see no serial on the barrel... the right receiver acceptance seems gone too? Try and do better pictures. If you feel like it take the rifle out of the stock and we can see if the barrel is original. WMO (Mauser) is distinctive, and so too are German ordnance spare barrels, - which the Turks received in some number.
Either way, thanks for bring the thread to the year 2021! (though a very discouraging year... but I am sure 2022 will be worse!)