I don't know about your short action rifle, but in the long actions, the ATR is different enough that it won't be easy. I have a 30 06 ATR and 338 4x4. The 4x4 has the rear action screw 1/8" further back (closer to trigger) than the ATR. The magazine box is sandwiched between the stock and action (a very poor design). You would need to swap to a 4x4 stock, if the bolt spacing distance is in fact the same on the ATR with the short action rifles. On top of that, the feed rails on the 4x4 are straight and open. The magazine holds the rounds down. The action would need opened on the ATR to use it with a 4x4 magazine. Honestly, I much prefer the ATR over the 4x4. If the ATR were chambered in 338, I would have certainly bought that and been much happier. The fluted bolt of the 4x4 isn't as smooth as the ATR bolt as it catches somewhat near the back end of the stroke. It's a gimmick in my view. The magazine box wiggles around in the stock of the 4x4 and my 4x4 wasn't accurate until I epoxied it into the stock. Of course now if the little plastic tab that holds the magazine in breaks, there's no way to remove the box. Also, the 4x4 forend is unacceptably flimsy. I had to rough it up internally and fill it with epoxy to stiffen it worth a darn. If only Mossberg would sell me a .338 barrel and bolt head separately for a reasonable price, I'd jump right on it and buy a long action ATR to swap to a 338. Basically, if you want a caliber that's offered in the ATR, get the ATR and not the 4x4. If you want something nicer than an ATR, don't get a Mossberg rifle because the 4x4 isn't nicer or better.
