CBTO and neck tension

[marchx]

I must confess not to segregate 6BR brass in separate containers according to the number of firings. My bad.

So, after cleaning my brass I anneal it (2.7s in my induction annealer. Tempilaq changes its colour at 2.6s). However in one batch of brass I can have 2 cases fired 3 times, 1 case fired one time and 30 cases fires 4 times. Even though I anneal the brass I think that still the brass fired one time has a different level of hardness than a piece of brass fired 4 times and annealed after every firing.
When I seat a bullet in a case fired one time the CTBO is 0.003 shorter in comparison to seating a bullet in a 4-times fired case (annealed).

In order to achieve the same CBTO I seat the bullets long and see where I am at. Then I adjust the final seating depth.
I understand that the difference in neck tension is still there. What should I do?

 

[rwj]

That small amount of difference could be attributed to the variation between bullets as your comparator and seating stem likely contact the bullet nose at different locations…

 

[bozo699]

Once annealed they should be the same or very close that’s the purpose of annealing. As stated above I would measure your bullets and sort them if that don’t work I would check the see if your shoulder bump is consistent if not fix that problem ,.. lube issues or die setup. Also do you have squeaky clean necks from using as pins or detergent? Or do you still have carbon in your necks?
Wayne

 

[marchx]

I measured the whole box of bullets. There was .001 difference in total between bullets in ogive, so not bad. I also measured the bullets 2 times to avoid error.

 

[marchx]

Once annealed they should be the same or very close that’s the purpose of annealing. As stated above I would measure your bullets and sort them if that don’t work I would check the see if your shoulder bump is consistent if not fix that problem ,.. lube issues or die setup. Also do you have squeaky clean necks from using as pins or detergent? Or do you still have carbon in your necks?
Wayne

I am wondering if I anneal them properly. Ok, I stop annealing .01s after tempilaq changes its colour. Too long? too short?I clean my brass in ultrasonic cleaner, I don't clean necks. When I use expander mander, I use redding dry lube. The shoulder bump is pretty much consistent- I encounter 0.001 variation. I have no idea what do you mean by die setup (I assume you mean seating die).

 

[Texas10]

You don't mention how much neck tension you're creating during sizing. Neck tension, neck internal coatings such as fouling, and surface finish all play a role in how much effort the seating stem will exert on the bullet, and that changes how much the stem will ride down on the ogive.
Another possibility is that your seating stem it actually pushing against the bullet meplat instead of the ogive, and variations in bullet OAL is what is driving your seating variations. Have you pulled the stem and checked the fit to your bullet of choice?

 

[rwj]

I measured the whole box of bullets. There was .001 difference in total between bullets in ogive, so not bad. I also measured the bullets 2 times to avoid error.

Can you measure length using the die seating stem that will likely contact closer to the bullet tip? If it’s contacting the tip as @Texas10 noted above, you’ll need a different one.

 

[HTSmith]

I measured the whole box of bullets. There was .001 difference in total between bullets in ogive, so not bad. I also measured the bullets 2 times to avoid error.

That is outstanding consistency! Do tell what bullets you are using.

 

[marchx]

Can you measure length using the die seating stem that will likely contact closer to the bullet tip? If it’s contacting the tip as @Texas10 noted above, you’ll need a different one.

I apologize but I don't quite understand why this should matter. The die is set up in certain way and the stem touches the bullet the same way every time. My question refers to consistency in seating bullets. In other word, I am interested in improving my process and excluding variations in seating depth.

 

[JFrank]

I must confess not to segregate 6BR brass in separate containers according to the number of firings. My bad.

So, after cleaning my brass I anneal it (2.7s in my induction annealer. Tempilaq changes its colour at 2.6s). However in one batch of brass I can have 2 cases fired 3 times, 1 case fired one time and 30 cases fires 4 times. Even though I anneal the brass I think that still the brass fired one time has a different level of hardness than a piece of brass fired 4 times and annealed after every firing.
When I seat a bullet in a case fired one time the CTBO is 0.003 shorter in comparison to seating a bullet in a 4-times fired case (annealed).

In order to achieve the same CBTO I seat the bullets long and see where I am at. Then I adjust the final seating depth.
I understand that the difference in neck tension is still there. What should I do?

Probably get torched for saying...I tried annealing brass at one time, my biggest take away was inconsistent seating after the deed. Now days I just brush the necks and wipe down the cases.

 

[rwj]

I apologize but I don't quite understand why this should matter. The die is set up in certain way and the stem touches the bullet the same way every time. My question refers to consistency in seating bullets. In other word, I am interested in improving my process and excluding variations in seating depth.

The issue is variation in the nose profile of the bullet. You're seating via the die stem that contacts the bullet at a different axial location than where you’re measuring the result. Any variation in the nose profile between these two contact points will be reflected as CBTO length variation.

 

[PhilKeil]

The issue is variation in the nose profile of the bullet. You're seating via the die stem that contacts the bullet at a different axial location than where you’re measuring the result. Any variation in the nose profile between these two contact points will be reflected as CBTO length variation.

I sort by take the seating stem out of my die. And sort by base to seating stem contact point. among other dimensions. It does not take very much change in the profile of the bullet for the tip of the bullet to contact the stem in a different spot or even not touch the meplat and just the tip to influence your results.

As i have jumped into this rabbit hole I have found with mass made commercial bullets manufactures hold tolerances in different areas of the bullet differently. ex manufacturer x bto may be closer than manufacturer y. but ogive to tip may vary greatly. conversely i have seen oal consistent but the bto vary.

That is why meplat trimmers and bullet tipping tools are made to uniform the mass made bullets after you sort them.

That is where the custom bullets come into play as well as the cnc offerings. Very consistant in all dimensions. good luck

 

[mikecr]

Maybe constant annealing isn't working so well.
You could take a break from all that. Like SPJ above

 

[marchx]

The issue is variation in the nose profile of the bullet. You're seating via the die stem that contacts the bullet at a different axial location than where you’re measuring the result. Any variation in the nose profile between these two contact points will be reflected as CBTO length variation.

How are you supposed to address this issue?

 

[marchx]

Maybe constant annealing isn't working so well.
You could take a break from all that. Like SPJ above

I am slowly playing with this idea.

 

[rwj]

How are you supposed to address this issue?

@PhilKeil said it well in his response above…

 

[Straightshooter1]

I sort by take the seating stem out of my die. And sort by base to seating stem contact point. among other dimensions. It does not take very much change in the profile of the bullet for the tip of the bullet to contact the stem in a different spot or even not touch the meplat and just the tip to influence your results.

Likewise, I sort based on seating stem contact point. Though there's variation between the BTO and the seating stem contact point, the issue for me is getting consistent seating depth at the base of the bullet, which is more import than the variations in jump that variations in CBTO will produce. And the best way to do with is sorting in this way. Of course, it's best when one can have both consistent CBTO and seating depth.

 

[1bamashooter]

That is outstanding consistency! Do tell what bullets you are using.

I'd like to know this too

 

[JFrank]

Likewise, I sort based on seating stem contact point. Though there's variation between the BTO and the seating stem contact point, the issue for me is getting consistent seating depth at the base of the bullet, which is more import than the variations in jump that variations in CBTO will produce. And the best way to do with is sorting in this way. Of course, it's best when one can have both consistent CBTO and seating depth.

How does ogive difference correlate to meplat? Heres is a ogive chart, wish I knew how to read it.

My rifle does, I dont.

 

[243winxb]

As the neck and shoulder are annealed, the case body is stress relieved, if temperature reaches 400F.

Keep brass sorted by lot & number of firings.