I have a Ultimate Shadow M70 in .270 WSM that is not shooting up to expectations. I found a new .300 WSM factory barrel for $35. Since I have a Super Shadow in .270 WSM that is a tack driver. My plans are this:

Replace the Ultimate Shadow stock with an Accuracy Innovations stock.

Replace the .270 barrel with the .300 WSM barrel. Is this a pretty simple job for my gunsmith? Correct me if I am wrong, it should just be a matter of swapping the barrel.

Should I have him true up the action while he is screwing the new barrel on?

I was going to sell the Super Shadow but can't part with it due to it's accuracy and this will give me a M70 in .300 WSM.

Thoughts?

It shouldn't be too much trouble to swap the barrels but you must check/set headspace. Just because the barrels came off the same model rifle doesn't mean the headspace will match; it might but most likely will not.

Racklover:

In theory you are correct about switching the barrels. In practice it is not so simple. If you face your action. The barrel tendon may or may not be to long. The original chamber may have to be reamed a little. The second reamer will not be exactly like the first. Factory take offs generally are not of the same precision quality as custom chambered barrels.
There are many headaches with putting factory take offs on another receiver. You have other considerations like barrel co-axial alignment and concentricity. you have concerns about headspacing, and if it is a blued barrel the finish may or may not have to be polished and re-blued, The stamped text may not line up above the stock. Most gunsmiths will tell you that you are gambling in geting quality accuracy out of a factory take off. Factory barrels are often sub quality in comparison to aftermarket barrels. In other words you get what you pay for. As for short magnums I personally would never use a short magnum in a factory take off as the barrel life on most short magnums is less than 1000 rounds. Especially if you don't know the barrels history. I would charge you you just as much to set back the factory barrel as I would to rechamber and instal a new barrel.
Longshot

Some time this morning I will call my gun doctor and see if it is worth doing this. I am told the barrel is brand new. It is S/S.

My smith wants $200 just to put the barrel on and check headspace

If it where me, i would face the action and then cut off 1 thread - how much I faced the action, (this is pretty simple) then rechamber with a GOOD reamer, using good technique..

the problem then becomes you are in it for nearly the price of installing a new barrel, or there about

jeffe

Come to Louisiana. I charge $115.00 for that. By the way correcting any headspace problems IS done BEFORE the barrel is put on. It's not a extra charge.