my current action is a long action,magnum bolt face.What is required to convert this action to a "long magnum" action,ie:.300 Weatherby,.375H&H,etc.Is it a simple and/or expensive alteration.Is this advisabile?Pros/cons needed.
Thank you,
Jim

The M70 magazine can be lengthened to the front (like the factory models), or to the rear, which most people prefer since it does not weaken the bottom lug recess and allows a more gradual feed ramp.

there's a small trick to it but that action can be lengthened (mostly) to the rear by removing the spacer in the rear of the magazine and some altering of the stop for the bolt.

I haven't done this but it's been described to me by folks that have. I'm convinced that you're better off to trade your gun for one that is already the way you want it.

If you choose to alter the action find a smith that will actually say that he HAS DONE IT.

The modifications that are needed are:Longer box and follower, the rear bridge needs to be milled rearward, the bolt stop and ejector need to be milled to say a 375 factory dimensions, the action behind the box needs to be modified (you can see the difference if you look at your two rifles side by side), the rails need to be modified at the rear, and a new forward scope mounting hole on the rear bridge will need to be added.

Winchester model 70 Classic actions that house the 30-06 family of cartridges as well as the belted short magnums utilize a shorter, or blocked long box than the long belted magnums. At the rear of the feed rails on these actions, behind the block in the box the rails tail inward. When the block is removed in an existing box or a longer box is installed, these "tails" prevent a cartridge from being dumped directly into the back of the box. Instead, the cartridge must be slid rearward under the tail. This same tail also prevents the rear of the cartridge from resting in the proper place and holds it down in the box farther than it needs to be. Feeding these cartridges into the box correctly, and ultimately having them eject properly, is also why the rear bridge should be milled rearward.

Chuck