Although I have never done an actual test of this, I noticed years back when I was barreling a lot of different rifles that it seemed to me that cut rifled barrels were significantly slower than buttoned barrels and the fastest by far were the hammer forged barrels by Remington, Winchester and Sako. Each adding about 100 fps to the former. So given my limited observations I would say that for a cut barrel to be 200 fps slower than a HF barrel would be about right. I discussed this at length with Bevan King and he agreed with my observation. He also told me that a buttoned barrel must be installed so the bullet travels in the same direction as the button was run through or velocity and accuracy suffered, and he would know.
It has to do with the internal finish of the barrel, the roughest being cut and the smoothest being HF. The good news is your barrel will smooth up as you shoot it and you can adjust your loads to get more velocity. The first major improvement happens between 100-200 rounds, then clean it good and remove any copper fouling and rework your loads you SHOULD be able to gain some velocity and then again after 500 rounds, the same procedure.
You can also accelerate this by hand lapping your barrels, but this is not something I have ever done so I will leave this process description to someone who knows the correct procedure, as I do not. I do know you can f**k up a brand new barrel if you don't know the correct way to go about it.
The different barrel "break in" procedures you will encounter on here from time to time are left over from the days when all barrels were cut rifled, and when applied to a cut rifled barrel, have some merit. They usually only involve a procedure with the first 10 or 20 rounds which no doubt does help some, but the more rounds down the tube the better it smoothes out and removing the copper fouling allows for this smoothing to happen faster.
