I see it all the time. Some tacticool Joe goes out and spends $1,500 on parts to build his AR15 and then puts a $30 scope on top of it. He then goes out and tries to make “sniper” shots and can’t hit the broadside of the barn. “its got a <fill in the name of some high priced barrel> on it. Why doesn’t it shoot well?” is always the follow up to which some harsh truth gets dropped on this poor soul.
When it comes to getting the best accuracy performance out of your rifle, ammo is the biggest influence over performance. After that comes optics, then trigger, and finally barrel. If we take a step back and think about what perfect accuracy is, it is the ability to send the bullet out the barrel over some distance and hit what we are aiming at dead center all in the matter of seconds. When in the barrel, the bullet doesn’t have much room to move around, but once it leaves the barrel all sorts of physics laws impart their harsh reality on it. If the bullet you are shooting has a low ballistic coefficient, then the bullet will go off course easier. Likewise, if your optic doesn’t provide a clear target image due to cheap glass or poor parallax adjustments, the barrel of your rifle may not be lined up with target even though the cross-hairs say they are. Last, but definitely not least, if your trigger is too stiff then what ends up happening is you apply so much pressure that you pull the barrel off target when the hammer gets released. All of these things can result in fractions of an inch change which translates to feet off target down range.
The bottom line is that the barrel has not as much influence on the overall accuracy of the gun as most people think. Yes having a barrel from a good manufacturer is paramount to accuracy, but to be honest its more about their QC processes than anything else. I have shot both high dollar rifles and budget ones and I have shot well and horribly with both. At the end of the day it’s your money and you get to decide what to do with it, just don’t be surprised if that $300 barrel with a $20 scope pairing doesn’t make dime sized groups.