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Topic: Neck Consistency/uniformness for Lapua Brass prep (Read 204 times) previous topic - next topic

Neck Consistency/uniformness for Lapua Brass prep

So after several reloading cycles and a decent variance in my ES/SD number i have started paying closer attention to each step. That being said my ES/SD numbers are in the mid single digits but i am trying to get them lower...

The problem: While prepping new Lapua brass i noticed that the necks have some flat spots. My only tool that  have currently is the depriming rod that came with my Redding FL/bushing die (does the necks and body in one pass). On that rod there is an expanding ball (i think that is what you call it) right before the depriming pin. When i find a case with this flat spot i run the through the "expanding ball a couple times to make everything circular. So after looking at the top of the neck i can see that even after i have passed it through the ball there is some small variance.

The question: How do ya'll make 99.9% sure that the necks are uniform? What tool do ya'll use to make this correction?

Re: Neck Consistency/uniformness for Lapua Brass prep

Reply #1
When you say flat spots do you mean its similar to when you drop a case and it falls on the neck and flattens out? Should that be the case then just running it throgh a Lee collet die will fix your problem.I do that if my cases fall on the floor and it turns out perfectly circular.

Re: Neck Consistency/uniformness for Lapua Brass prep

Reply #2
When you say flat spots do you mean its similar to when you drop a case and it falls on the neck and flattens out? Should that be the case then just running it throgh a Lee collet die will fix your problem.I do that if my cases fall on the floor and it turns out perfectly circular.

Yeah that is exactly what i am talking about....

Re: Neck Consistency/uniformness for Lapua Brass prep

Reply #3
I wonder what's causing the flat spots? I'm sure it's not the rifle chamber, tumbling maybe?

I don't use Lapua brass, the only time I've seen out-of-round necks is when I mess up while lubing and send a few to the garage floor. The Lee collet puts them back in line.
Chris

Re: Neck Consistency/uniformness for Lapua Brass prep

Reply #4
Wow, if your ES/SD are in the single digits, whats the problem
People would kill to have that. It doesn't mean everything, but
your very lucky and shouldn't worry about getting them lower.

You can buy a custom sized mandrel or just buy one
they are tapered and just run it down far enough to straighten
out the mouth.

https://kmshooting.com/case-neck-expanding/expanding-mandrel-kits.html

Re: Neck Consistency/uniformness for Lapua Brass prep

Reply #5
So after several reloading cycles and a decent variance in my ES/SD number i have started paying closer attention to each step. That being said my ES/SD numbers are in the mid single digits but i am trying to get them lower...

The problem: While prepping new Lapua brass i noticed that the necks have some flat spots. My only tool that  have currently is the depriming rod that came with my Redding FL/bushing die (does the necks and body in one pass). On that rod there is an expanding ball (i think that is what you call it) right before the depriming pin. When i find a case with this flat spot i run the through the "expanding ball a couple times to make everything circular. So after looking at the top of the neck i can see that even after i have passed it through the ball there is some small variance.

The question: How do ya'll make 99.9% sure that the necks are uniform? What tool do ya'll use to make this correction?
What rifle are you shooting? Some autos will flatten a spot on the neck but I have never seen a bolt do it. Single digit es/sd means you should be teaching the rest of us not asking us. I have been lightly using the small Lee crimp die and getting good results though I only occasionally get single digits.

Re: Neck Consistency/uniformness for Lapua Brass prep

Reply #6
First off, good job on single digit standard deviations.  As this statistic gets smaller (approaching zero) it becomes harder to determine if the differences are significant.

Let's look at a five shot string: 2800, 2805, 2810, 2815, and 2820.  The standard deviation is estimated at 7.9.
Let's look at a three shot string: 2800, 2801, and 2815.  The standard deviation is estimated at 9.4.

Because of the small sample sizes it is difficult to determine which group is better.

Using five shot groups to estimate the standard deviations is more robust.  When we are trying to isolate an effect of variation (i.e. neck consistency) we may test the variances.  Five shot standard deviations can be calculated with higher confidence in determining significantly different outcomes.

Let's form a hypothesis stating that sub standard casing necks are causing more variation in terms of velocity.  How can we be sure?  Run a small scale isolated experiment where the only factor we are altering is the introduction of sub standard casings.  Let's say five shots of good necks and five shots of bad necks.  What are the standard deviations of the two strings (control = good neck and treatment = bad neck)?

This example tests them for significance.   SD1 (bad necks) = 9.  SD2 (good necks) = 4.  The factor to remember and use with 5 shot strings is 3.4 (write that down).  9 squared equals 81 and 4 squared equals 16.  81 divided by 16 equals 5.1.  5.1 is larger than 3.4 so bad necks have significantly more variation in velocity than good necks.  If the outcome of our variance test is less than 3.4 then the hypothesis is most likely false.

For reference (somebody will ask), the factor to use for 3 shot standard deviations (you're too good for that) is 5.4 (from the F tables).  Too add credence (pun intended) to any test, repeat the experiment and see if you get the same results. 

I have my doubts about putting too much faith in a chronograph.  I try to know where my load is, always track my three shot group from a cold bore, and not run out of H4350.  That's more than enough factors for me come Monday morning.

Good luck isolating the cause of the flat spots (pictures always help and are more entertaining) on your casing necks.
  
See you at the range.

Re: Neck Consistency/uniformness for Lapua Brass prep

Reply #7
Sometimes if you have a really stiff ejector spring when you pull the case from the chamber once it comes out the ejector slams it again the action wall creating a flat spot on the case neck
Grant

Re: Neck Consistency/uniformness for Lapua Brass prep

Reply #8
Never had that issue with the Lapuas going through my Bergara HMR
In adversity remember to keep an even mind, train hard and fight easy.
                            Horace and Alexander Suvorov

Re: Neck Consistency/uniformness for Lapua Brass prep

Reply #9
Sometimes if you have a really stiff ejector spring when you pull the case from the chamber once it comes out the ejector slams it again the action wall creating a flat spot on the case neck
Truth. This would happen on my TAC30.
RIP Chris Cornell

Re: Neck Consistency/uniformness for Lapua Brass prep

Reply #10
I have to agree with Lathoto above. 

If you really, really, really already have ES in the mid-single digits a 20 shot string you're already reloading with the best in the world and the number of shots you're going to have to fire to figure out if doing something differently will get you from 5->4 probably isn't worth the effort.

Now if you occasionally shoot a 3 shot string with an ES of 5 but if you actually go measure 20 shots and its an ES of 30, its going to be much easier to diagnose and improve upon.

So I gotta ask - which camp do you really fall into?

Re: Neck Consistency/uniformness for Lapua Brass prep

Reply #11
Only thing I would add to what’s been said is if your on several firings your brass is probably getting work hardened and needs annealed. I can usually start to feel the difference in the sizing step when my brass starts getting hardened and needs annealed. Everyone that reloads has a diffrent  take on annealing match guys may anneal every firing or every other, once every third firing maybe enough to preserve accuracy I usually go every 5-6 firing or more on my 223 brass and about every 3rd on my 6.5 I don’t own an annealeze so its a pain in my a/:$$ to do it more often.