Hornady Neck Wall Thickness Variance

[P_Mo80]

Question about neck wall variance in new (unfired) batch of Hornady 308 Match Brass:

Wall thickness Average = .029
68% were within a .001 variance
32% were within a .0015 variance

With this brass, I'm going to be on bench and nothing more than 600 yards. Is the .0015 variance acceptable (won't cause a run out issue that will affect accuracy within that 600 yard range)?

 

[Howland]

Did you get your numbers by subtracting .308 from loaded round neck thickness? It sounds like it because those measurements would be very thick. I'm guessing they would be half that.

If you're pinging steel or just trying to get the most out of your rifle at 600 yards I would not worry. If you're planning to compete in matches you might end up turning necks or at least using a mandrel to final size your necks. Or maybe neither. Let your targets tell you. Are you even measuring concentricity or just neck thickness?

 

[straightshooter1]

Question about neck wall variance in new (unfired) batch of Hornady 308 Match Brass:

Wall thickness Average = .029
68% were within a .001 variance
32% were within a .0015 variance

With this brass, I'm going to be on bench and nothing more than 600 yards. Is the .0015 variance acceptable (won't cause a run out issue that will affect accuracy within that 600 yard range)?

Yes, that neck variance can cause enough run out to effect "precision" at 600 yds. Whether that's really an issue depends on whether you're trying to get in an X-ring on a target or just ringing steel. If you're just ringing steel at that distance, the amount of run out induced by that variance shouldn't be much of an issue.

That variance is pretty normal for a lot of brass. And I would say in your case, you can mitigate the run out from it if you use the brass processing technique of running an expander mandrel through the neck to set your neck tension. Doing this will move the variations mostly to the outside, which helps in reducing the bullet's run out. If you're using a bushing die type sizing die, that bushing tends to move that variance to the inside, especially if you're also not using an expander ball. The best approach, IMHO, if you're using a bushing die is to not use an expander ball and let the bushing size down the neck and then use an expander mandrel to size the neck to the neck tension you want.

 

[Steel head]

1.5 thousandths neck variance is actually pretty decent for non premium brass.
Really a non issue unless your shooting BR or high level f class.

You really need a ball micrometer to measure neck thickness properly.
I’m guessing you’re measuring across loaded rounds as it should be .012-.018 thick and half of .029= .0145 which in the normal range.
if your getting .0015 across the neck variance your brass is in the premium brass range of variance.

 

[DMP]

May I suggest you weigh sort. The last time I used Hornady, I had six cases in a lot that were 7 grains lower than the next lowest weight.

 

[Steel head]

May I suggest you weigh sort. The last time I used Hornady, I had six cases in a lot that were 7 grains lower than the next lowest weight.

Most of the variance is on the rim cut.
weight sorting is a waste of time.
Volume sorting is a better option if you want to be picky.

 

[vinniedelpino]

I'd get a collet die and go from there.

 

[P_Mo80]

Yes, that neck variance can cause enough run out to effect "precision" at 600 yds. Whether that's really an issue depends on whether you're trying to get in an X-ring on a target or just ringing steel. If you're just ringing steel at that distance, the amount of run out induced by that variance shouldn't be much of an issue.

That variance is pretty normal for a lot of brass. And I would say in your case, you can mitigate the run out from it if you use the brass processing technique of running an expander mandrel through the neck to set your neck tension. Doing this will move the variations mostly to the outside, which helps in reducing the bullet's run out. If you're using a bushing die type sizing die, that bushing tends to move that variance to the inside, especially if you're also not using an expander ball. The best approach, IMHO, if you're using a bushing die is to not use an expander ball and let the bushing size down the neck and then use an expander mandrel to size the neck to the neck tension you want.

Good info ... I was thinking of approaching it via the use of an expander mandrel. 2 thousands of neck tension calls for the use of a .306 mandrel, correct? Do I need to accomodate for spring back? If so ... half a thousandth (.0005)?

 

[P_Mo80]

1.5 thousandths neck variance is actually pretty decent for non premium brass.
Really a non issue unless your shooting BR or high level f class.

You really need a ball micrometer to measure neck thickness properly.
I’m guessing you’re measuring across loaded rounds as it should be .012-.018 thick and half of .029= .0145 which in the normal range.
if your getting .0015 across the neck variance your brass is in the premium brass range of variance.

Yea, I used a Hornady Vernier Ball Micrometer. Ok, that is good to know! thank you!

 

[P_Mo80]

Did you get your numbers by subtracting .308 from loaded round neck thickness? It sounds like it because those measurements would be very thick. I'm guessing they would be half that.

If you're pinging steel or just trying to get the most out of your rifle at 600 yards I would not worry. If you're planning to compete in matches you might end up turning necks or at least using a mandrel to final size your necks. Or maybe neither. Let your targets tell you. Are you even measuring concentricity or just neck thickness?

I used a Vernier Ball micrometer ... each side was averaging .0145 ... I just reported it as it's combined thickness.

 

[straightshooter1]

Good info ... I was thinking of approaching it via the use of an expander mandrel. 2 thousands of neck tension calls for the use of a .306 mandrel, correct? Do I need to accomodate for spring back? If so ... half a thousandth (.0005)?

If you're not annealing, yea . . . .0005 would be a good allowance to get to the .002 your after. So, you're probably going to want to go with a .3065 mandrel.

 

[P_Mo80]

and I do anne

If you're not annealing, yea . . . .0005 would be a good allowance to get to the .002 your after. So, you're probably going to want to go with a .3065 mandrel.

Ok, and I do anneal, will that reduce the amount of spring back?

 

[straightshooter1]

and I do anne

Ok, and I do anneal, will that reduce the amount of spring back?

Annealing will reduce the amount of spring back. Too much annealing and you'll not have any. Too little annealing will not. When I anneal my .308 cases (typically Lapua, Peterson or even Federal), I get very little spring back, which often doesn't show up until the next day or so.

PS: I use a .3065 mandrel to get the .0015 neck tension I'm after for my .308 and I turn my necks to get a uniform .014 thickness.