Neck Measurement(s) Questions

[Intheshop]

First thing that happens here on every new barrel.... be it a factory(assembly) gun or replacement...

The chamber's ID neck diameter.

Two types of small hole gages. There's the "std" full ball and then there's the flat bttm style. Choose the latter. I use an aluminum arrow that's a mild press fit on the gage's knurled end. Aluminum vs tool steel of gage is a no brainer.... the arrow ain't gonna scratch the tool. This allows for measuring assembled brrl/action.

From there it's pretty elementary to make precision measuring of the existing chamber. Once that's been recorded .... now we have a target number for loaded round neck OD..... which gets recorded. Make notes...the more the better. But until you have those two numbers you're just chasing tail.

 

[Coyotefurharvester]

What/how are you measuring the inside neck diameter? What is the +- error of your measurement tool?

 

[Gargoyle]

First thing that happens here on every new barrel.... be it a factory(assembly) gun or replacement...

The chamber's ID neck diameter.

Two types of small hole gages. There's the "std" full ball and then there's the flat bttm style. Choose the latter. I use an aluminum arrow that's a mild press fit on the gage's knurled end. Aluminum vs tool steel of gage is a no brainer.... the arrow ain't gonna scratch the tool. This allows for measuring assembled brrl/action.

From there it's pretty elementary to make precision measuring of the existing chamber. Once that's been recorded .... now we have a target number for loaded round neck OD..... which gets recorded. Make notes...the more the better. But until you have those two numbers you're just chasing tail.

What is optimal clearance between loaded round and ID of chamber neck?

 

[Gargoyle]

What/how are you measuring the inside neck diameter? What is the +- error of your measurement tool?

Digital calipers

 

[Intheshop]

What is optimal clearance between loaded round an ID of chamber neck?

That's what you're trying to figure out. Each barrel/bullet/load is going to have it's likes,and dislikes.

Me telling you what makes bugholes with HV cast in any one of my rigs isn't doing you a bit of good. I change bullet diameter,moreso than skimming or turning necks. You are going to have to test in your rig. Make the adjustments,for instance neck tension far enough apart to actually be measured. Say,.002 vs .004 . Just sayin,your cases are going to have a hard(haha) time distinguishing very small changes..... well,at least until you've done the foundational work.

 

[Gargoyle]

That's what you're trying to figure out. Each barrel/bullet/load is going to have it's likes,and dislikes.

Me telling you what makes bugholes with HV cast in any one of my rigs isn't doing you a bit of good. I change bullet diameter,moreso than skimming or turning necks. You are going to have to test in your rig. Make the adjustments,for instance neck tension far enough apart to actually be measured. Say,.002 vs .004 . Just sayin,your cases are going to have a hard(haha) time distinguishing very small changes..... well,at least until you've done the foundational work.

So, brass has springback of .0005" generally? If the case neck expands to fill the ID of the chamber neck and springs back .0005" couldn't one just add that for the chamber neck ID?

 

[Bronsin]

Digital calipers

There's the descrepancy. Calipers aren't precision enough to give you an accurate number for what you're measuring. Digital or not.

 

[Straightshooter1]

ID of sized neck .305"
Bullets OD .3085"
.3085" minus .305" = Difference .0035"

OD sized neck .3375"
OD with bullet .3395"
.3395 minus .3375" = Difference .002"

In popular terms of "neck tension" which do I say is my neck tension?

Did you use the same case?

What instruments did you use to take these measurements?

If you're using a caliper, you're not going to get very accurate ID measurements. And if you're using two different cases, there could be significant difference in the wall thicknesses. Putting it all together, it's easy enough to have that kind of variation.

 

[Gargoyle]

Did you use the same case?

What instruments did you use to take these measurements?

If you're using a caliper, you're not going to get very accurate ID measurements. And if you're using two different cases, there could be significant difference is new wall thicknesses. Putting it all together, it's easy enough to have that kind of variation.

Calipers. I did different cases. I used a new case, measured the same case and came up with .002" (OD of sized case neck vs OD of loaded case neck) I also see the tips of the calipers read different than the large flats.

 

[Gargoyle]

There's the descrepancy. Calipers aren't precision enough to give you an accurate number for what you're measuring. Digital or not.

Is it not a relative measurement?

 

[gunsandgunsmithing]

What is optimal clearance between loaded round and ID of chamber neck?

This dimension is far more critical if it's too tight vs too loose. IOW, a little looser won't hurt but too tight or no clearance can cause accuracy problems or become dangerous if the case can't expand.
General rule of thumb..no less that .002" clearance and I like to keep it no more than .004.
You've got some room there that makes it "good enough" if you just use a fired case to get a measurement from. Course, that first round is the one that you don't have yet. Generally, there's a print or the previous owner is of help there. If not, I cheat and turn one thin in a lathe, without regard for quality, just that it fits easily and then fire and measure. And, you can use a moderate load for this first firing. Some basic knowledge of the cartridge you're fooling with is part of it, like..not many 6ppc's that won't chamber a .260 loaded round. So, that or a tad thinner is what I'd look for on that first one.

 

[Gargoyle]

This dimension is far more critical if it's too tight vs too loose. IOW, a little looser won't hurt but too tight or no clearance can cause accuracy problems or become dangerous if the case can't expand.
General rule of thumb..no less that .002" clearance and I like to keep it no more than .004.
You've got some room there that makes it "good enough" if you just use a fired case to get a measurement from. Course, that first round is the one that you don't have yet. Generally, there's a print or the previous owner is of help there. If not, I cheat and turn one thin in a lathe, without regard for quality, just that it fits easily and then fire and measure. And, you can use a moderate load for this first firing. Some basic knowledge of the cartridge you're fooling with is part of it, like..not many 6ppc's that won't chamber a .260 loaded round. So, that or a tad thinner is what I'd look for on that first one.

Fired is coming in at .345" measured 5 cases like clockwork .345". My loaded rounds are .340".

 

[Bill Norris]

Fired is coming in at .345" measured 5 cases like clockwork .345". My loaded rounds are .340".

.005 is plenty of room for bullet release.

 

[Bronsin]

Is it not a relative measurement?

No, and the reason is because calipers aren't accurate enough to reliably give consistent results. The jaws on them used to measure the I.D. of a hole are notoriously bad, and brand doesn't matter either. No one in the machining Industry trusts the ID measurement of calipers for anything that requires real precision. They're good for measuring a drilled hole, but that's about it.

If you know the OD of the neck before and after seating a bullet, that's really all you need anyway. Knowing the ID of the case neck is redundant.

 

[Gargoyle]

No, and the reason is because calipers aren't accurate enough to reliably give consistent results. The jaws on them used to measure the I.D. of a hole are notoriously bad, and brand doesn't matter either. No one in the machining Industry trusts the ID measurement of calipers for anything that requires real precision. They're good for measuring a drilled hole, but that's about it.

If you know the OD of the neck before and after seating a bullet, that's really all you need anyway. Knowing the ID of the case neck is redundant.

OK, F those IDs then!

 

[gunsandgunsmithing]

OK, F those IDs then!

Yes...case ID's. They mean nuttin

 

[Gargoyle]

I'm all happy with the Redding FL die "neck tension" at .002. I read/see where the expander button isn't the best way (pulling up through the case) to set the case neck. Supposedly mandrels are better for that. SO I think I should:

1. Get a Lee decapper die
2. Get 21st Century mandrel holder and .305, 3055 mandrels
3. Size with Redding die with button removed

 

[gunsandgunsmithing]

Then, a check to make sure you have what most call sufficient clearance is if a bullet slips inside of a fired case with no resistance.

 

[gunsandgunsmithing]

I'm all happy with the Redding FL die "neck tension" at .002. I read/see where the expander button isn't the best way (pulling up through the case) to set the case neck. Supposedly mandrels are better for that. SO I think I should:

1. Get a Lee decapper die
2. Get 21st Century mandrel holder and .305, 3055 mandrels
3. Size with Redding die with button removed

Some use mandrel and some don't. Long story and you can do a search on here but you don't have to use a mandrel at all. Are your dies bushing dies? You can control neck tension with the bushing without any mandrel or rod touching the neck. Been done for ages that way.

 

[Gargoyle]

Then, a check to make sure you have what most call sufficient clearance is if a bullet slips inside of a fired case with no resistance.

They slip in and out just fine!