I think ER Shaw will make them too but they have a really long wait time. I'm not sure about other makers. I don't think the mag opening in the old flat rear receivers is long enough. Now Savage did make RUM's and STW's on the old actions but they had longer openings/boxes in them than the standard long action. Others on here who have done it have had to cut a little out of the mag opening to get the longer mag to fit. And all I've seen have had to cut and extend their current mag box too. I think the easier way to do it is with the new center feed actions. The mag box is not attached to the receiver and the mag opening in the receiver is slightly longer. I have one and a 300 Weatherby round will fit in it. All that is needed is to cut a notch out in the front of the mag box to allow clearance for the bullet noses and it will still clear the feed ramp.