What ever the legal limit is, for a rifle, is too short. If it is 16", then 16" is too short. X7 barrels at 24", are not too short.

In my experience 300 yard is stretching it for a 50 caliber rifle. What is happening out there is the bullet is slowing through the speed of sound, and it doesn't seem it will be as accurate out there, as it was at shorter ranges. My mind tells me this, and so does actual shooting. However 45 caliber rifles may be accurate a way beyond 300 yard, because their bullet, at 300 yard, are still traveling a way faster than the speed of sound.

So..............in my opinion accuracy is not limited by barrel length. Accuracy is limited by the range at which the bullet slows to the speed of sound.

Actually, my opinion is, a shorter barrel is more likely to be accurate, than a longer barrel. A heavy barrel is more likely to be accurate than a lighter barrel. Accuracy suffers when the bullet slows through the speed of sound. Just my opinion.