the 5R milspec is based on the M24 sniper rifel.to me from what I can see and say is this.the barrel used to make a 5r milspec is one that did not make it to a M24.and by not useing it for the M24 they put it on an action to sale to use.they started this in 2003 I think may be wrong.
was told one time the barrel and rifeling was built around a 168gn SMK.but most who own one finds out it will shoot a 175gn SMK just as good if not better.the twist is 1:11.250 the rifeling has a rounded face ( not flat )allowing the bullet to travel down the rifeling better with less copper build up.I can say from owning one it does clean up really fast.
I will all so add that the rifel is a great shooter with any type of bullet.even when one can not reload it shoots about anything.but most who do not reload buy the FGMM ammo.eith in a 168 or a 175gn load.but when one can reload its a whole different world.been able to load with a 168gn VLD,168 gn SMK,175gn SMK,and now a 208gn A-max.all give me very good accuracy.just seems to shoot anything you want it too.and thats with little time and effort with the loads of choice.
now,Remington does offer the barre in one or two more rifels.they are not stainless though.forgot just what they are.will have to look and see just which two they are.but for me I would just get the 5R and walk away from the others.the cost is $1000 +/- and you have to get your FFL guy to go through Acusport t get one.or find one on a gun site of some sort.Remington does not show in any way that they even build it.why I cannot say or haven't been told.but they make about 250 each year.so geting one can be hard at times.
as of two years ago the offer two different cals.a 223 with a 1:9 and a 300wm with a 1:10 twist.and both have the same rifeling as the 308.and that the other two rifels/cals shoot just as good.
OK just looked up the other two rifels.one is a M700 Taregt Tactical.sorry its just one other rifel.but both the 5R and the M700 Target Tac have hammer forged 5R rifeling.and yeah almost forgot to say.the 5 stands for 5 grooves.
OK,I hope that I have said just what you wanted to hear.or atleast tried to.