The whole point of the nut is to swap barrels as desired, for me it makes experimentation easy (calibers, rifling twists and style, contour, length, etc.). Here is what I started with: Everything can be swapped in and out as needed:
Savage Precision Target Actions. Many more have been added since:
Don't forget that the Savage, 783 Remington, and I believe the Shilen action, can have bolt heads exchanged for complete cartridge family swaps. Here is a dual port Savage action, loads from the left and ejects on the right, that was set up for .243 WSSM and is one of the most accurate varmint rifles I have, delivering groups of around .187" for 10 shots at 100 yards when I do my part and not shooting in gale force sleet in Oregon.
Then this can be extended to Remington 700 actions. This one was a bare 700 Action from Brownell's with a Pac-Nor barrel and nut that uses the Savage wrench, the action was equipped with Greg Tannel's dual pin recoil lug, and had the bolt bushed and sleeved:
The above rifle is shown here with a .308 Winchester Pac-Nor 1:10" twist polygonal rifled barrel, but also has a Pac-Nor .22-250 Remington Ackley Improved barrel, that uses the same .308 Win. magazines.
If you are a glutton for punishment, even the Remington 783 can be modified, here with a Criterion .25-06 Remington barrel and nut from Northland Shooter Supply, and Boyd's stock tricked out, the OEM .30-06 barrel is shown below:
And just for giggles and wows, even the ubiquitous AR-15 platform can be cobbled together with different barrels (made around separate uppers), such as this one with a Hart 24" 1:9" twist .204 Ruger barrel with no gas port so it functions as a bolt action. In this case a side cocking upper receiver is used. Since this photo was taken this rifle has blossomed into three, with uppers in .223 Wylde, all as bolt actions. All shoot at or below .5" at 100 yards, are not assault weapons and great for varmint:
Sometimes I feel like a nut, and it's just too much fun. Barrels are from Brux, Criterion, Hart, Krieger, Pac-Nor (their polygonal rifled barrels are superbly accurate) and Shilen. Have it your way. I was considering the Shilen action but never got around to buying one.