The reason they developed excessive headspace, and the occasional blow up was because of the lengthened magazine.
The front, or feed ramp of the magazine cutout in the action itself was expanded forward to accomadate the longer cartridges.
This in turn weakened the action in the area of the bottom front locking lug recess. When lengthened in this manner, the bottom lug on the bolt is not supported as well as on a standard length M 98, and the action is weakened.
For a .300 H & H, or a .375 H & H, and SAAMI pressures, or whatever the pressures the factory uses, I would consider the actions to be okay and safe. To the best of my knowledge factory loads of the above two mentioned cartridges are not loaded all that hot, anyway.
At high pressures, such as some full length Weatherby cartridges and some wildcats, it is not recommemded.
