RE: 257 roberts/imr 4350?
There use to be a sticky that covered situations like this. Its gone now so I'll say it,You need to work up your own loads. If someone states a particular load you should always check your reloading manuals and see where it falls. If its anywhere near the Max you should start at your manuals beginning load and work up carefully.
A load that shows no signs of excessive pressure in one rifle may very well be dangerous in yours.