The culmination of Mauser’s efforts was his Model 98 rifle adopted by Germany in April 1898. Mauser 98 commercial sporters were developed soon thereafter and were introduced at about the turn of the century. Made in rifle and carbine versions, they were produced by
either Waffenfabrik Mauser (Mauser Arms Co.) in Oberndorf am Neckar, a town in southwestern Germany, and are often called Oberndorf
Mauser sporters for genuine high quality Mauser commercial sporters or by small custom gun-makers using factory or military inspection reject actions and or later military surplus actions.
The Mauser firm calls them “genuine” or “original” Mauser sporters to set them apart from the many inferior rifles made up with factory-rejected, out of spec or worn but still usable military parts. Most if not all early original commercial Mauser specimens are marked Waffenfabrik Mauser A.-G. (A.-G. Stands for Aktiengesellschaft, which means Limited or Inc.) on the
receiver ring. Those produced later have the markings Waffenfabrik Mauser or Mauser-Werke A.G. on the receiver’s left wall. Some later specimens bear the
Mauser banner trademark on their receiver rings. Mauser Co. markings are also on many original Mauser actions used by
Rigby and various other reputable gunmakers that produced sporters. The
popular term Mauser 98 sporter can be considered generic, but it is often taken to mean an original Mauser sporter.
Smaller gunsmith made inferior rifles made up with factory-rejected or worn military actions tend to be un-marked or scrubbed of markings besides the mandatory proofing marks.
Metal finish of the above action and bolt do not match the higher quality typical of pre-war sporting/commercial Mauser rifles. Also all genuine Mauser made German commercial actions were serial numbered and proofed marked on the left side of the action above the wood line.
And the bolt on this rifle is not fully serial numbered on the top of the bolt handle as was the practice for genuine Mauser commercial bolts.
The “2,75g G.B.P. S.G.” stamp on the receiver means it was proofed with 2.75 grams of Gewehr Blattchen Pulver (Military Flake Powder) Stahl-mantel Geschoss (steel jacketed bullet). This marking was used between 1899 and 1901 specifically at the Suhl proof house and should indicate 8mm Military issue ammo as the calibre and round it was proofed for. This is very likely a surplus rifle that was modified later by a commercial company to be a sporting rifle. It was pretty common in Europe between 1890 and 1960 as so many outdated military rifles existed.
Another reason I know it is not a real commercial Mauser sporter is where it was proofed at. Many custom made up Mauser 98 rifles were produced in Suhl by the many and various gunsmiths located nearby unlike genuine commercial Mauser's (which were all typically proofed at the Mauser factory in Oberndorf), custom or small lot contracted rifles often show Suhl these proofs indicating non Oberndorf heritage.
2.75 grams, which is approximately 42.4 grains is the mark which signifies the rifle was proof tested with a standard service proof charge of 2.75g of flake powder and a steel-jacketed bullet at the time.
The lack of a nitro proof (always seen with crowns over and in front of the N after the “2,75g G.B.P. S.G.” stamp) on the above wood-line also means it was not a commercial proof. The crown over the N on the bottom of the receiver means it was a military made action. This specific marking formula was commonly used before 1912.
And it usually designates the earlier 8x57mm (often 8x57I or 8x57J, with a .318" bore).
Pure speculation on my part, but the cartridge it is still chambered for is very probably the time honoured 8x57mm Mauser and if the date we surmise is correct it is most likely the earlier .318 groove diameter rather than the later 1905 military adopted .323 groove diameter unless later changed but then it's proof would have changed too.
Appears to be just another pre-WW1 military surplus or factory reject but still serviceable refinished action.
Here are some examples -
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