True regarding force exerted by the base of the bullet and that the force is applied to the lugs.

However, if one removes metal from the feed ramp, and if one removes metal from the front portion of the action opening to allow for a longer magazine to be fitted, then the amount of metal supporting the lower lug is reduced and the action is accordingly weakened. Many standard length mausers have been converted to shoot .375H&H and other long magnums with varied success and some consider the practice of removing metal from the lower front of the action acceptable. Nevertheless, if you remove metal from the area of the action that supports the bolt lugs then you have a weaker action and that is not the best way to go. The proper thing to do is to chamber an action for a cartridge comparable to one for which it was originally designed. That's why mausers were made in different sizes.