.223 Lapua Case Neck Thickness Grows After One Firing

[Fire4Effect]

I have been using a variety of different manufacturers of .223/5.56mm brass such as Winchester, IMI, IVI and Lake City. I had been turning the necks on the aforementioned brass and found on many cases that portions of the necks were below 0.011”. Some almost 0.010”. I found this unacceptable and decided to move to Lapua 223 Match brass. I found the Lapua case necks varied from 0.012” to 0.013” as I moved around the circumference and turned the necks on the new brass to 0.012”.

After firing and resizing the cases I found the Lapua necks were 0.013”. I have never seen the neck thickness on any of the previous manufacturer’s case necks grow after one firing. Can someone explain what is going on?

Thanks

 

[243winxb]

After firing and resizing the cases

Gun, load & dies used may help? Did you brush the crud out of the necks ID before taking measurement?

 

[Fire4Effect]

I decap, clean primer pockets, brush out neck and run in a vibratory cleaner for several hours. Then I anneal and run in the vibratory cleaner again before resizing. I use Whidden full length resizing dies.

Firearm: Daniel Defense MK12.
Brass: Lapua 223 Match.
Primers: CCI #41
Powder: 23.6gr IMR 8208 XBR
Bullets: 77gr SMK

 

[Chubbs]

Is there carbon still on the inside of the necks after cleaning or do you wet tumble.

 

[boltfluter]

The neck needs to be squeeky clean to get an accurate reading. As we know .001 is very small.

 

[fkimble@charter.net]

The .013 case neck pic shows a case that looks crooked, not on the spud square, this will add to the apparent measurement.

Frank

 

[Fire4Effect]

I just measured some twice fired TZZ 91 cases from a few weeks ago that were neck turned to 0.011” after being once fired. They had the identical load as the aforementioned loaded Lapua brass and the necks measure exactly 0.011” after the second firing. Carbon is obviously not the issue.

 

[Fire4Effect]

The .013 case neck pic shows a case that looks crooked, not on the spud square, this will add to the apparent measurement.

Frank

Looks can be deceiving.

 

[Fire4Effect]

Is there carbon still on the inside of the necks after cleaning or do you wet tumble.

Vibratory cleaning always leaves some carbon behind that is not significant.

 

[Fire4Effect]

The neck needs to be squeeky clean to get an accurate reading. As we know .001 is very small.

I only vibratory clean. I tried ultrasonic cleaning and the squeaky clean case necks cased problems with seating pressure.

 

[Fire4Effect]

The only difference between the Lapua case necks I turned and the IMI, Winchester, Remington and IVI case necks I turned are that the Lapua cases were unfired and the other cases were once fired before neck turning. All the once fired cases were unchanged after once or multiple firings.

 

[RegionRat]

By chance, did you take a measurement over the loaded round on the first turn, and if so, did those numbers agree with the tube mic?

Sometimes the two values are close when the cut is smooth, but sometimes the dimension over the bullet are the real story because of the surface defects causing differences in the contact area under the mic anvils.

Surface roughness and waviness can affect the differences in measurements. The two line contacts of the flat anvils tend to ride differently than a line against a compound radius between the two styles of measurements. If the ball anvil of the tube mic settles into a valley and punches in, it gives the impression of a lower dimension compared to the line contacts of being measured over a bullet.

Depending on the smoothness of my cut, I have seen some noise in the measurement method that accounts for several tenths, nut not a full thousandth. My picky BR friends will usually take a second pass after the first firing after the turn, and that is enough for even the picky folks.

If the before/after difference issue is as large as 0.001", then a second cut will clean the whole surface if the first turn cleaned the whole surface. If the second turn just takes off high spots, it could be that the first turn was just a little rough. But either way, it isn't uncommon for picky folks to take a second pass.

If you didn't take a number over the bullet the first time, I would take one the next time to compare to the value with the tube mic.

 

[Fire4Effect]

By chance, did you take a measurement over the loaded round on the first turn, and if so, did those numbers agree with the tube mic?

Sometimes the two values are close when the cut is smooth, but sometimes the dimension over the bullet are the real story because of the surface defects causing differences in the contact area under the mic anvils.

Surface roughness and waviness can affect the differences in measurements. The two line contacts of the flat anvils tend to ride differently than a line against a compound radius between the two styles of measurements. If the ball anvil of the tube mic settles into a valley and punches in, it gives the impression of a lower dimension compared to the line contacts of being measured over a bullet.

Depending on the smoothness of my cut, I have seen some noise in the measurement method that accounts for several tenths, nut not a full thousandth. My picky BR friends will usually take a second pass after the first firing after the turn, and that is enough for even the picky folks.

If the before/after difference issue is as large as 0.001", then a second cut will clean the whole surface if the first turn cleaned the whole surface. If the second turn just takes off high spots, it could be that the first turn was just a little rough. But either way, it isn't uncommon for picky folks to take a second pass.

If you didn't take a number over the bullet the first time, I would take one the next time to compare to the value with the tube mic.

Thank you for your thoughtful response.

I solved the mystery. I decided to turn the necks again, but this time set the cutter slighter larger than 0.013” and gradually bring it in. Upon first contact with the neck the cutter removed a thin band at the mouth of the neck and at the neck shoulder junction. I decided to take a measurement before cutting more and the case neck measured 0.012”. It was the narrow raised portion at the mouth of the neck that was measuring 0.013” and distorting the overall case neck thickness measurement.

I tried chamfering the outside of a case mouth to see if that would remove the raised area, but it did not. I will run the entire lot of cases back through the cutter to make them consistent.

Thanks everyone that took the time to read my post and consider my question.

 

[Fire4Effect]

Further research has identified what is creating the increased thickness at the case mouth. Prior to receiving the Lapua brass I used a bushing die to give me the neck tension I desired. My standard Whidden full-length non-bushing resizing die reduced the neck diameter to .244”, but I needed .243”, which my Whidden full-length bushing resizing die achieved. I did not use a mandrel after resizing because the only expanding mandrel I had was a .223”.

To allow me to finish using the preferred process I ordered a 23st Century .221” expanding mandrel, which I started using with the new Lapua brass. After going back through all the steps and measuring at each step I have identified that the 23st Century .221” mandrel was creating the thin raised area at the case mouth.

 

[RegionRat]

Glad that worked out.
I would still be of the opinion you should study both the numbers from a tube mic, as well as the dimension over a bullet, once you are settled in with your prep process. Good Luck!

 

[boltfluter]

I only vibratory clean. I tried ultrasonic cleaning and the squeaky clean case necks cased problems with seating pressure.

Fire,
I agree. This recommendation was only for getting an exact reading, for your test. Happy shooting.
Paul

 

[butchlambert]

Fireform without a bullet first and before turning