The typical sleeve for the rem 700 action is made from aluminum and the ID is made just tight enough to slip a Rem 700 action into and glue it in place. The ones I have seen are generaly 1.5" OD and a bit longer than the action this allos for alot more area to be bedded or glued to the stock depending on how the sleeve is made. The extra diameter and length help make the action a good bit stiffer than factory which helps alot if your planning to use a big heavy barrel and float the whole barrel.
Another reason is the look , they make your factory action look like a high end custom action.
I haven't seen a sleeved action in a good while , I think that with the great customs that can be had for such reasonable prices now days your kinda wasting your money spending $200 on a good sleeve , $350 for the action , and another $150 to have the action blueprinted , then you have to deal with having the stock cut out and bedded wihich will run up to $300. Buy this time you could have bought a Lawton !!
