what is the proper rate of twist for a 7mm Rem Mag Barrel?

Really depends on if you’re going to go with any of the super bc target/hunting bullets BUT 1-9 will do anything you need with conventional hunting bullets. I built a 1-11 280 AI years ago and accuracy was only so so with 140’s (what I wanted to shoot) but exceptional with 100gr Sierra hp’s. Not terribly useful. I’d just use a 1-9 and call it good.

F Class shooters using 284’s are still using 9 tw, 8 to 8.75 tw being more common for heavy 180gr and up target bullets but that 9 tw will work for most every hunting bullet out there now.

Is this a good deal? large enough muzzle for a 7 Mag?

Douglas premium chrome moly 7mm cal.9 twist,finish at 25",.630 muzzle.$190 plus shipping.

A .630 muzzle is big enough for a 40 caliber. Way more than you need for a 7mm. A 9 inch twist is all you will need.
Pressures at the muzzle are very low. Look at some double rifles; paper thin muzzles.
Where are you getting douglas barrels that cheap?

dpcd

A guy was selling it on another forum. Somebody else just now beat me to it. Probably a good thing anyway if the muzzle is too large.

Maybe change to a .358 norma instead. what is the proper twist on one of those?

No the muzzle was not too large: you asked if it was large enough; it was.
Forget about the muzzle diameter and get a barrel that weighs as much as you want and is as long as you want.
That barrel was a medium to heavy sporter weight, probably.
12 or 14; factory twists are 16 which are fine but some of the longer 250 grain bullets need a faster twist.

It is pretty easy to make a fat barrel thinner. Pretty tough to do the opposite. Regards, Bill