So Tim, are you going to add a second recoil lug and stock bolt? I know you don't have it in hand yet and J has mentioned about it being a single shot but I have seen where the sides of the mag well are milled away for most of their depth to get the width to keep the cartridges under the rails.
I have no doubt you have things well in hand but this is an interesting piece on the Mauser magazine layout
Many thousands of Mauser 98’s have been rebarrelled to a multitude of modern cartridges very different to the original 7.92mm German military chambering.
While some of these conversions feed reliably from the magazine, many do not!
The fault often lies with the magazine and follower profile if it is left unaltered from the original layout.
Paul Mauser was a gifted firearms designer who carefully designed each magazine of his M98 rifles for a particular cartridge.
Box and follower dimensions were predicated on case dimensions... Paul figured that a staggered column would enable more cartridges to fit into a given magazine well than a single vertically stacked column.
In order to feed correctly from a staggered magazine, each cartridge needed support... from the magazine box on one side and a cartridge or the follower on the other side and underneath. With a stacking angle of 30 degrees, three stacked cartridges in contact would form the corners of an equilateral triangle:
By multiplying the Cosine of 30 degrees ((0.866) by the case head diameter, then adding the diameter to the product of the equation, the correct magazine box width could be determined.
For example, a 9.3x62mm case measures 11.95mm across the rim.
So 0.866 x 11.95 = 10.35 +11.95 = 22.3mm
Theoretically, that is the correct inside rear magazine box width for any cartridge deriving from the 9.3x62mm case.
However, all cartridges taper, and so must the magazine.
The same formula yields the proper box width at the point of shoulder contact:
The shoulder diameter is 11.45mm
So 0.866 x 11.45 = 9.92 + 11.45 = 21.4mm
A magazine box for a 9.3x62mm cartridge must therefore theoretically taper from 22.3mm to 21.4mm. Adding an extra 0.07mm ( 0.003") or so for dirty or oversized cases makes practical sense.
So a practical magazine box for the 9.3x62mm cartridge would taper from 22.4mm to 21.5mm
A magazine box designed for one cartridge works for others ONLY with the same identical front and rear diameters and the same span between them. Triangles between cartridge centrelines get steep when the box is too narrow, and rounds tend to cross-stack.
Paul Mauser also relieved the box sides slightly, from just ahead of the cartridge base to just behind the shoulder, so there would be no increase in friction between the case body and the box wall.
He lavished equal attention on the magazine follower, which on an original M98 mirrors the box taper.
The width of its lower shelf matches that of the case, with a 61 degree step between the upper and the lower shelf.
The top shelf is high enough to touch the next-to-last cartridge without lifting it off the last round in the stack (its half a diameter above the lower shelf at base and shoulder) The follower has a slope to follow case taper and keep the cartridges level in the box.
Side clearance of the follower to box is also critical.
Followers should be about 1.5mm (0.060") narrower than their boxes so they can wriggle a bit... especially important for the last cartridge.
A magazine follower for our 9.3x62mm example cartridge must therefore theoretically taper from 20.8mm to 19.9mm.
A magazine follower to fit the practical box above would taper from 20.9mm to 20.0mm
Floor plates that have been machined to hold the magazine spring tightly won't feed properly either... the springs are supposed to shimmy back and forth!
If the spring can't shuffle a bit as the bolt strips a round, it twists and the follower tips or ends up sideways... sometimes both!
Follower length is not as critical, but one that is too short will tend to 'dive' in the magazine box and cause misfeeds.
Many temperamental-feeding custom rifles have had some attempt at magazine alterations, often made on trial and error rather than based on sound engineering principles.
Getting a custom M98 rifle to feed flawlessly with a new chambering is the mark of a top-notch gunsmith who fully understands the ‘elegant simplicity’ of Paul Mauser’s original design.