This is from my experiance and may be different from what other members have noticed.
But it seems to me the most results of buying a used barrel will be one of the following:
- Some will lock up and have side to side play. These have potential for a
lot of fusteration trying to get to shoot accurately. Especially if you are using a synthetic forearm. A shim behind the forearm spacer of a wood forearm can help fix this, but is usually only temporary. And accuracy will diminish over time.
- Some will lock up but will have slop between the hinge pin area and barrel lug.This pretty much means that either you or the person before has taken off too much metal from the end of the lug were it meets the hinge pin. In this case you will most likely need to make a metal shim. More info on that in the FAQ's.
-Some will fit up, but will not lock up all the way.These are among the easiest to fix IMO. As they will usually only require you to file off just a tad off the end of the barrel lug area where it meets up to the hinge pin. A round file will be what you need.
When you go to lock it up, hold you rifle side ways and look at were the chamber area of the barrel meets the receiver and hold it up to the light. You will most likely see light at the top half of the barrel, but the bottom will be touching the receiver. Meaning you need to take off ever so lightly, a bit of metal off the lug. Be careful as to not taking off too much, an go slow.
- Some will lock right up without a problem.Enough said

Over all chances I have had are pretty good. And usually will need only slight mods as I mentioned above.
Give it a try. You can always sale or trade off the barrel here to other members.
-Aaron