I can only speak directly to Contender handgun barrels. In factory TC barrels, my Super 14 223Rem shoots really well, sub 1inch 5 shot groups are the rule. My Super 14 30-30 with a brake shot 1inch to 1.5 inch 3 shot groups pretty regular. My 10inch 22 Hornet (later re-chambered to a K-Hornet) was so-so. Sometimes around an inch but often closer to 2 for 5 shot groups with many different loads. My Super 14 44Mag will keep them in about an inch and half for 3 shots although I have done very little load testing so it may do better if I tried. These are all handguns shot off a rest at 100 yards. I had a couple of acquaintances that were big into Contenders for awhile and tried them all. They swore by MGMs. One had some trouble with a Bullberry 222 that had to go back eventually.
I did have a Virgin Valley (early MGM) Encore rifle barrel in 17 Mach IV that shot very well once I got a pillar-bedded forend on it. 5 shot groups less than a half inch were pretty common.
If accuracy were my goal from the beginning I would order an MGM but that's not to say a factory barrel won't shoot well enough.
