Watched this video by John Barness.

Don't have fancy equipment like concentricity gauges but a few things were said in the video find difficult to believe.

John states that a bullet shot out of a case without concentricity within 0.002" will result in the bullet spinning lopsided down the barrel and poor accuracy.

It is difficult for me to believe that a bullet will oscilate once engaged by the rifling. Bullet goes into rifling and is put straight.

My experience is the largest factor for good accuracy is the consistency of velocity that the bullets exit.

The barrel whips during the shot and having the bullets exit at the same rate is most important.

I haven't seen the video, but a recent article in Handloader magazine showed that damage to the base of a bullet had significantly more impact on accuracy than damage to the tip of the bullet.

I can believe that a bullet that doesn't enter the tube perfectly straight could deform slightly when impacting the rifling... I can see accuracy degradation occuring - how MUCH is up to debate. I suspect that depends on a great many other variables...

As to barrel whip? Dunno. Go case a barrel in concrete and let me know!

AR Corey,

Consider that the degree of inaccuracy which is being discussed is not quite as great as it may sound. For extreme accuracy it is a known and proven fact that concentric bullets, both structurally and as a loaded component are more accurate than lopsided. In the long range accuracy games, most competitive shooters agree that around that .002 cutoff is where the dedregation of accuracy begins.

In several articles Barsness has said <.005
runout for big game rifles and less <.003 for varmit/target rounds. I believe what happens with too much runout is bullets can enter crooked and get slightly deformed when jamming into the rifling affecting accuracy. This is the same concept of why it's generally a good idea to seat bullets close to the rifling vs further away (bullet has less chance to lean slightly).

Lou

Corrected to say Barsness recommends no more than .002 at case neck to ensure runout at bullet would be less than .005.

Lou

Okay understand now.

Deformation of bullet can cause flight problems.