I am building a second AR for Accuracy at distances of 3 to 600 yards.  I am looking at working with White Oak Armament.  Does anyone have experience shooting a 20" SPR and a 20" Varmint.  I would like to know what kind of shot group difference I can expect.  Ideally I would like to lighten the weapon without sacrificing accuracy.

Quoted: I am building a second AR for Accuracy at distances of 3 to 600 yards.  I am looking at working with White Oak Armament.  Does anyone have experience shooting a 20" SPR and a 20" Varmint.  I would like to know what kind of shot group difference I can expect.  Ideally I would like to lighten the weapon without sacrificing accuracy.

I am no Expert... But, from what I know 20" is going to be pretty short. In reality you won't get full velocities until you get out about 24" in most cases. But, If you reload... You could go with a 22 or 23" barrel. ANd since you are looking for that 600 range... I won't suggest anything under 24"s Good luck in your quest... You may try maybe a lighter 24" barrel??

Accuracy you can get but, velocities in a 20" will be hard.... Thus making it mosre difficult to judge the drop on the bullet.....

I have a 20" varmint WOA and its shoots in the .40's. A SPR is a 18" and my buddy has one (WOA as well) and it is a good gun but we havnt tested it out to its full potential yet.

Quoted: I am no Expert... But, from what I know 20" is going to be pretty short. In reality you won't get full velocities until you get out about 24" in most cases. But, If you reload... You could go with a 22 or 23" barrel. ANd since you are looking for that 600 range... I won't suggest anything under 24"s Good luck in your quest... You may try maybe a lighter 24" barrel?? Accuracy you can get but, velocities in a 20" will be hard.... Thus making it mosre difficult to judge the drop on the bullet.....

A 20" is PLENTY of barrel for 600 yards.
A WOA SPR barrel is PLENTY accurate.  

There have been LOTS of threads on this site of ARFCOM members with 16" RECCE's and 18" SPR's shooting some AMAZING groups at 600 yards and beyond.

When you're talking about this type of accuracy, it all comes down to whether a .35" group is good enough, or a .25" group is worth the extra 2lb of barrel

If I were building a rifle to fill the role you describe, I would use an 18" WOA SPR barrel with the mid-length gas system from ADCO.  ADCO also has 20" WOA barrels as well.

For what it is worth my current build is a 16" Lilja Recce because the only thing I will lose is FPS's and I reload so I can work with that. I shoot a 60gr VMAX at 3050fps with Varget out of my 20". You loose about 100fps going to a 18". Good luck