My experience of one, is that they are as good as any other except for perhaps the very top end barrels from Hart or Krieger.
My .257Roberts built in 1984 used an E.R.Shaw barrel with the "so called" 3" Roberts chamber. It was installed on a 1938 LaCarouna M98 action that was milled, drilled and tapped, turned down Brownells bolt handle installed, and polished and blued with a 400grit finish (very deeply polished blue). A Timney "Sportsman" trigger was also installed. The finished metal was put into a Bishop #3 grade stock that was finished with a hand rubbed finish and checkered with an extensive pointed pattern similar to the Remington M700 Mountain rifle. Finished rifle weighs 7.25lbs with 2x-7x Leupold Vari-X II in Leupold bases and rings, WITH 5rds and sling.
The finished rifle will get 3,100fps with a Hornady 100gr PtSpt over 48.5gr of H4831 and has shot more than one sub 1" 3-shot groups at 200yds. 5-shot groups at 100yds usually ran to about 0.75" After I let it develope some mid-bore pitting, (long story, involves an extended hunt in very wet conditions) It will still shoot MOA until bore gets copper fouled.
In 1987 I dropped a white-tail doe at a surveyed 345yds, and in 1993 a Mule deer at 390yds along the Marias River in uppper Montana. I also have killed the two biggest deer I've ever killed with that rifle. The rifle has also taken over 100 deer over the past 26years.
I've been satisifed with my E.R.Shaw barrel.
If OEM means that it's as accurate as my Remington 700ADL express (sporter taper barrel and synthetic stock) with Remington "OEM" barrel which will "on demand" put 5 Sierra 50, 55, or 63gr bullets into 1/2" or less at 100yds , then OEM is good enough for me.
However, if you want "mediocrity" in a barrel, get an Adams&Bennett. My MkX Mauser in .338/06 is a 2moa barrel. But, it kills anything that its fired at if I do my part. Barrel and installation by gunsmith still cost me less than $100 in 2003. Barrel cost $60 on clearance from MidwayUSA. I still think I paid too much........ gunsmith only charged me $40.00 to screw it on and finish ream the chamber.