Measure the Remington varmint barrel at the muzzle and then go the barrel makers contour
charts and find one that is the same or slightly smaller if you dont want to open the barrel
channel on your stock.
Barrel maker use different systems for size comparisons and you just have to look and compare.
There are 3 basic shapes of barrels, Straight cylinder, Straight tapered and contoured. Most
factory barrels are contoured.