First things first.
Not meaning to be "preachy"...Just like you can't make a winning dragster, dirt bike, or race car by just putting on a bigger carb, your rifle is a SYSTEM and each component needs to be optimised and work with the rest to make a "winning" shooter.
Check out the Sticky's, and FAC's...they are full of information to "accurize" your NEF.
Make sure the forearm is on solid...follow the recommendations posted in the stickys. You might have to free float, full bed, use an O ring, or a combination, and make sure you have full contact with the locking lug. Bedding the barrel to the receiver and shimming will also increase your accuracy by a bunch. NEF's are just as tough or tougher to get to shoot well as any other rifle, you just have to follow all the things others have done.
Forget about barrel polishing for right now...vertical stringing is usually caused by other factors...forearm, load combination, seating, how you hold and how your set the rifle on the bags or if you use a bipod, all the looseness associated with NEF's, and your shooting ability, so you need to address those factors BEFORE you mess around with barrel polishing...It might help, but for the most part trying to polish a barrel without knowing the reasons or haphazardly will only RUIN a barrel and isn't any guarantee to reducing stringing to boot...
I'm working with my 22-243 Encore right now and I can go from vertical stringing to horizontal stringing to nice round 1" group to bughole group just by changing the bullet seating, bullet brand and weight, powder or primer and using unprepped to benchrest prepped brass. This rifle has had all the accuracy "tricks" done to it plus I installed a pillar bedding system for the forearm. There isn't any quick fix to ANY kind of stringing unless it is only in the forearm, then sometimes it is just full bedding, full free floating, rubber O ring or a combination of them. I wish there was an easier way to "benchrest" accuracy, but there isn't.
Start from the beginning...fix the forearm, then do some load testing...at 100 yds...50 yards doesn't mean much as the bullet hasn't settled yet, except to see if your sights are good enough to keep the bullets on target at 100 yds or beyond. While you are doing the forearm you can fix any problems with the locking lug, bed the barrel to the receiver with steel epoxy and make sure the headspace is good. Takes about a weeks worth of time spread over 3 weekends or so if you are a working soul.
Work on seating, powder type and amount, primer brand and your shooting ability. Change only one parameter at a time...i.e., increase or decrease powder by .3 at a time for this size cartridge, change seating by 0.005", etc., and fire 3 round groups until you find that "sweet' spot, then you can go to 7-10 round groups to see how they perform. Shoot 7-10 groups then clean well and I recommend WipeOut for a thourough cleaning at that time, and always clean between powder changes. Shoot groups of ONE parameter change at a time so you have a record of the group change with the parameter change and not a bunch of mixed messes you can't make any kind of assessment with. Always fire a 3 round control group after you fire a 3 round fouling group and keep the fouling group so you know where the bullets are going from a cold barrel.
AFTER these things are done you have the basis for determining an accurate load. Benchrest prep the ammo then be sure the rifle is set up on the bags right. THEN AND ONLY THEN will you be able to determine and correct "stringing".
GOTO
http://www.6mmbr.com/index.html and
http://www.freewebs.com/precisionrifle/accuracyarticles.htm, and visit some of the long range shooting forums, they are chucked full on "insider" information on how to get a rifle and ammo to shoot the best.
Personally, when I'm developing a load I shoot 3 round groups starting in the middle of what a reloading manual lists for the bullet and powder. After I find a good group I fire one or two 7 rounds groups then go hunting, why waste time, money, components and range time trying to get the "perfect" load when none really exist. I will stay with this load for a few hundred rounds as long as I'm hitting more than missing. Once things go sour I will shoot another 7 round target to see whats going on, then futz aroud with the seating...usually going out first in 0.005" increments because the throat usually get chewed up and seating out will solve the problem quicker than futzing with power amounts.
If you don't want to do these things, spend the money to have a good gunsmith "accurize" the rifle, otherwise change ammo brands to see if one shoots better than another. Each rifle likes a certain bullet weight, or brand.
The whole accurizing process, rifle and ammo prep, is nothing more than doing things to change the harmonics of the barrel so the bullet exits the barrel at a null node not right in the middle of a big vibration...in other words it doesn't "flip" the bullet in any direction.
All the information needed to solve your problem is available on this and other sites. You have to realize your rifle ISN'T a benchrester and anything around 1" to 1 1/2" is about average unless you happen to get an exceptional rifle. Tuning the rifle will get you down to the 1/2" - 3/4" range as long as the ammo and your abilities allow this and this accuracy has to be worked constantly to keep it.
Welcome to the wonderful world of NEF rifles.
Good Luck
'Njoy
