View Full Version : measuring case necks

04-12-2016, 10:53 AM
There is a good thread going on now "neck turning of cases" and this question pertains to that thread, but I did not want to hijack.

I come from the J.M. school of case making :cool: (Al Nyhus, Randy Robinett, Mike Bigelow), so I feel my case prep procedure is pretty sound. However, I have found that when I measure my case necks, with a seated bullet, that the measurement changes based on where I put the micrometer. If the micrometer is closer to the mouth the measurement is smaller. The farther back (towards the shoulder) I go = the bigger the measurement. It is very difficult to get a repeatable measurement even on the same round let alone on different rounds. :( However, all rounds follow the same basic trends. I have found this to be true on all 3 of my bench rifles (LV 30BR, HV 30BR, Hunter 30x47) Is this normal? The monkey wrench is that 2 of these rifle setups are shooting really well. The 3rd one I am still developing.

Just curious what you have to say before I talk to the "Jedi Masters" at the next match.

Thanks in advance for any thoughts/replies

jackie schmidt
04-12-2016, 11:03 AM
If your bullet has a "gas ring" at the base, then where ever that ring happens to be in relation to the neck is where it will measure the largest. When turning your necks, this has to be taken into consideration.

Some brands of custom bullets exibit hardly any gas ring, while others might be as much as a half thousandth of a inch+ larger than the rest of the bullets body.

If your neck's wall thickness is does not vary, and the loaded round measures what you want it to at that point, don't worry about it.

Boyd Allen
04-12-2016, 11:05 AM
When you turn your necks, is it done with a hand held tool or do you force them over a mandrel on a lathe, that turns with the case?

04-12-2016, 11:43 AM
Jackie - I shoot BIB bullets and the pressure ring on the 112-7 measured .3086 on my micrometer. Not sure what his 118-10 measures, I think it is pretty closer to that.

Boyd - I use a mini-lathe with a case holder that your wrote about (forgot the name) - has a little rubber gasket that goes in the primer pocket. I had Roger Miller at K&M shooting make me several mandrels/pilots? (I get mandrel and pilot mixed up a lot) in .001 increments that go into my K&M turner to fit the inside of my case necks.

In my process, I inside neck ream following my case neck expansion (after running the cases through a resizing die with a bushing as close to the neck diameter that I can get). I have several reamers (in .001 increments) made by Wilson. I want to barely touch the mouth of the case but get rid of the "funnel" shape as you progress down the case necks.


Al Nyhus
04-12-2016, 07:10 PM
Hey Jason...is your micrometer a tubing mic. or does it have flat anvils? -Al

04-12-2016, 08:28 PM
When measuring case necks over a seated bullet;

Look where the end of the bullet body expands the case neck. In good light this is easy to see. Measure ONLY in that area, actually about 2/3 or 3/4 of that area.

If you notice closely there are 3 diameters visible in the resized case neck. First where the bullets major diameter is visible, and where the neck sizer stops, and, the area between where the sized area ends and the case shoulder.

You only need to control where the bullet body resides. The other two diameters are not of consequence to performance or safety.


04-12-2016, 09:08 PM
Seat three bullets at three different depths,
now measure at the base of each seated bullet,
and see if they are the same.

04-13-2016, 09:55 AM
"I can get you a toe by 3 o'clock - with nail polish" :D
2 flat anvils. Miss you Al!
My idear is that maybe I am not taking out all of the "funnel" when I inside neck ream?

Cmaier - that is a good idea - thanks. I will try it this summer. I have a match coming up in 2 weeks and don't really want to change my seating die. Yea - I know I can always put it back - just something I don't want to mess with right now.


jackie schmidt
04-13-2016, 10:25 AM
Hey Jason...is your micrometer a tubing mic. or does it have flat anvils? -Al

I can't understand why you are getting a "funnel" inside your necks.

When you turn neck, the turning mandrel extrudes the inside of the neck straight, which is then transferred to the outside diameter. You cut this irregularity way when you turn the necks.

The only time I have seen reaming the inside of a neck to be of any use is when a shooter necks a
Case up or down to change caliber size and is wanting a no-neck-turn case. Then all of the irregularities would be transferred to the necks ID.

Reaming necks when making a 6PPC from a 220 Russian or a 30BR from a 6BR seems counterproductive if you are using a chamber that requires the necks to be turned.

04-13-2016, 11:21 AM
Thanks Jerry. I will try that tonight and see if I can get more consistent results.
Thanks for the reply Jackie. I always appreciate what you have to say.
I do not know why the funnel occurs - but it happens when I expand from 6 to 30. If I stick my K&M pilots/mandrels in the case neck (without neck reaming) they get "stuck". The bigger the diameter of pilot, the farther up the neck they get stuck. I do not have pin gauges, so do not know the actual dimension of the "funnel". If I try and turn without reaming - it seems like I have to push really hard to get the pilot in the case neck (maybe it was pushing the material out - like you mentioned?) - I did not think that was good. That was when Al talked to me and mentioned neck reaming. Inserting the pilot is a pretty smooth feeling after reaming.

Al Nyhus
04-13-2016, 12:30 PM
Jason, remember that when you push the shoulder back to resize and it comes back forward again when fired, that brass wants to go somewhere...usually wants to 'creep' up the neck. Especially if the cases have enough 'stress relief' done to them ('annealing', for lack of a better term). Ain't a bad thang...just a thang. ;)

"Put the piece away, Walter...they're callin' the cops!" :cool:

04-13-2016, 05:29 PM
Is your neck turning mandrel matched by the same manufacturer as the mandrel on the neck expanding die?

Sinclair actually mentions this in their catalog under 'Sinclair Stainless Steel and Carbide Mandrels.
"Turning mandrels are sized .002" under bullet diameter and expander mandrels are .001" under bullet diameter.
Had a similiar problem that went away when I purchased the 2 correct mandrels from the same manufacturer.

Butch Lambert
04-17-2016, 07:17 PM
Jason, fireform a couple pieces of your new brass without a bullet. I personally use Bullseye and a wax plug. It leaves you less to expand and makes a better neck.

04-17-2016, 10:42 PM
If the largest neck measurment is less than the chamber neck measurement you're good to go. Forget about everything else and think about something more pleasurable. You stated that the rifles shoot pretty good...why worry about something that bothersome when it really doesn't matter?

I suspect that you're sizing way too much but some feel the need to do that and it doesn't seem to hurt anything...

Boyd Allen
04-18-2016, 10:39 AM
When I use the Bullseye method, for my .262 neck PPC barrels, I expand to .22 and turn to about .010 first. this leaves me less expaning (but some) to do. It is the axial force that happens during expanding that causes case necks to become cocked. By reducing the amount of expanding done with a mandrel, cases are straighter, which gives more uniform results and a more even cut on the shoulder.

04-21-2016, 06:03 PM
So fireform a 6BR with Bullseye and wax plug, then expand and turn to appropriate diameter?
Thanking you in advance, willy

Butch Lambert
04-21-2016, 06:15 PM
I'm not answering for Boyd, but that is how I do it. It takes very little to finish expanding the neck and does not push the neck to the base of the case. My brass is about .015 longer doing it this way.

Boyd Allen
04-21-2016, 07:07 PM

I am a little confused by your mention of a 6BR. The whole bullseye and wax plug is for making 6PPC brass from .220 Russian cases that involves quite a bit of blowing out to the 6PPC chamber. I would NOT try to use the identical procedure for cases that start out as the same caliber as the chamber that they are to be fired in. For those, I would simply chamfer the necks, lube their IDs, expand them with an expanding mandrel that was a proper match for my turning mandrel, turn, and then load them with the powder that I planned on using and a suitable bullet. Again, I would not use the Bullseye and wax plug for your situation. With the case fill of Bullseye that I use for making 6PPC cases from .220 Russian, I think that it would be likely that you would end up with too much pressure. I am half way up the shoulder. You are in an entirely different situation.


04-21-2016, 08:47 PM
Dial indicator with 1/10,000 graduations.

04-29-2016, 06:47 PM
Boyd ,
Sorry for the confusion, If I'm not mistaken, Apollo asked about his 30BR loadings? My inquiry was for 30BR also. Thanking you in advance.