Sorry, had not seen the previous thread on this issue -- "Magazine Geometry"



In the current issue of Peterson's RifleShooter magazine, there is an article on the Mauser 98. It gives some history of Paul Mauser and his inventions and production of the rifles. It is all very positive and favorable.



There is an extensive section on the magazine design and its details. How each caliber had a custom designed magazine for it to ensure reliable feeding. It describes calculations based on cartridge headsize, shoulder size, and body length. Again, the whole article is very favorable.



The article implies that converting one caliber Mauser to another caliber would require changing the magazine box to ensure reliable controlled-feeding.



The implication is that a 7x57 Mauser rifle converted to 257 Ackley Improved could have serious magazine feeding issues unless the magazine dimensions were properly modified. The problem seems not limited to cartridge length but to magazine box width compared at various points along the length of the cartridge.



This may all be common knowledge to others (or complete garbage), but it was news to me. (I am not a gunsmith. I don't even turn scope mount screws.)



If I consider building a rifle on a Mauser 98, or a Montana 1999, will I have to specify the exact cartridge to get the right magazine ? I was under the simplistic notion that as long as cartridge headsize and cartridge length were the same, I could build any caliber on the Mauser 98.



How sensitive is this magazine box issue ?



Hammer

Hammer,
Go to page 4 of this forum. There is a long thread on this subject titled "Magazine Geometry". Mucho good info there.

Craigster,

Sorry, had not seen that thread.

Hammer

Are the mathematics and configuration issues described specific to Mauser actions or are they also applicable to push-feed actions ? Guess they are not applicable to straight-line feed magazines.

Hammer

Besides the magazine box width and length, and siderail alteration, you also have to take into account the length of the opening in the bottom of the receiver. If you go with a longer magazine, or if you file the length of your magazine longer, you can end up with a lip in the front of the opening that can cause problems unless you grind and polish it out.



Blue

Changing from 7x57 to 257 Roberts or 6mm Rem. would probably not cause feeding problems because the "Bob" and the 6mm Rem are based on the 7x57 case.

Changing to the Ackley Improved versions will probably require at least some feed rail milling to feed at all, and indeed widening the magazine @ the shoulder area will probably be necessary for "flawless" feeding.

I have a K98 that has been rechambered to 8mm-06 A.I. The feed rails were milled by Harry McGowen when the chamber was reamed. Feeding of the top round w/"4 down" has been finiky unless COL (3.34") was kept @ least .040" less than the inside length of the magazine box. (3.80")

When loaded "4 down", the case head portion of the cartridges would "float". (not be forced up under spring tension) After reading the "Magazine geometry" thread as well as the article in Rifle Shooter, it became obvious to me that the larger diameter of the Ackley Improved shoulder was the source of this problem. According to the formula in the article, about .012" will need to be milled from each side of the magazzine @ the shoulder area.

From my personal experience with this "Ackley Improved" application, the "formula" seems to "hold water", and explains some of the glitches I have encountered.