Why does smaller necks improve accuracy?

[crunch]

Many of you turn the neck smaller to gain accuracy. I was curious as to why doing this improves accuracy.

 

[Cheechako]

crunch

The primary reason to turn case necks is to ensure concentricity. Much brass has lopsided neck wall thickness which puts the bullet off center with the bore. That's a bad way to start the bullet on it's way.

Another reason to turn necks is to match the loaded neck diameter to a custom chamber neck. For example, if you have a chamber neck that is .265" you would strive to make your loaded cartridges with a .263" diameter. That .001" on each side is more than enough to allow the bullet to release from the neck and it also means that you will need a very minimum of neck resizing to seat a new bullet. less resizing means brass longevity.

Turning case necks becomes wasted effort beyond a certain point. It generally does little to nothing in a factory rifle. Turned necks for Grandaddy's 30-30 will produce absolutely no gain. Even such cartridges as the 30-06 may see little gain from it. It's only when you get into the super accurate Benchrest and varmint cartridges that you will realize results. Even then we may be talking about shrinking groups only by .125" to .250" at best. But that is enough to move you from first-loser to first-place.

Ray

 

[DickG]

Turning necks for concentricity aids accuracy, turning necks smaller only increases amount brass is worked. You must also typically have a smaller neck size chamber to reap the full benefit.

Dick

 

[acloco]

If you have a small neck chamber, you must turn necks.

But, IMHO, the biggest advantages of turning necks - necks are coencentric now,inside & outside circles are round and have the same center point) AND...the bullet pull is the same all the way around.

In all of the reloading operations, you are trying to remove variables. Round necks with the same bullet pull on top of straight brass is the goal.

 

[mysticplayer]

Besides what has been mentioned, I neck turn to improve consistency of neck tension which makes for truer bullet release. The assumption is that if the neck material is the same thickness, it will have the same level of elasticity releasing the bullet in a more 'true' manner.

In factory chambers and reg commercial brass, I just want to clean up 80% of the neck as getting necks too thin will lead to neck splits.

Sizing and seating concentricity will pay much great dividends then a bit of neck turning in a SAAMI chamber - too much slop.

Jerry