Full Length or Neck Only; What's Best Resizing for Accuracy?

[Mram10us]

Don't dies have to be smaller than chambers? If their dimensions match the chamber, they cannot size fired case dimensions smaller.

Rimless bottleneck full length sizing die headspace, for example. They're typically. 004" to .005" less than the cartridge GO headspace gauge. Measure your die's headspace to see what it is.

I'm guessing he means hone so you don't have the saami .001" wall slop??? That's what I gathered.

edit: correct the .010" to .001"

 

[Alibiiv]

Hear is my take on this.
All necks should have a minimum of .004 thousandths clearance to the neck chamber to allow the bullet to be released without pressure going up. Tight neck to chamber dimensions can work if you load down. This will help align the bullet but cost lots of velocity. Also when running a tight neck chamber the case necks must be turned.

So if the neck clearance is .004 and the necks have been turned, the bullet will have to rely on case fit. the better it fits the chamber, the better the bullet will align with the bore.

I started loading buy just full length sizing and about the best I could get was 1/2 MOA. Wanting/needing better accuracy, I started full length sizing just enough to feed well. Accuracy improved again. When I joined this group, I went all out and used/tried everything I knew and what I was told about loading accurate and consistent ammo.

That is when I realized that i couldn't miss a single step. Some have had better luck than I apparently with full length and no neck turning, but not me. I also really found out what my ammo quality was when I bought a concentricity tool from Sinclair. that tool made me re evaluate my dies, press and technique.

Some have questioned why some others are not satisfied with 1/4 MOA, and I cant answer for others, but that's just what I want. I want to get where I can stay well below that consistently if possible. don't know if I can do it but for sure I can't if I don't try.

J E CUSTOM

Question, how do I determine "case neck clearance"? I don't have a copy of the blueprint for the reamer, it's a .270 AI, and getting a copy of the reamer blueprint is not an option as the gunsmith does not have one. Can the case neck clearance be determined from measuring a fired case?

 

[Bart B]

I'm guessing he means hone so you don't have the saami .010" wall slop??? That's what I gathered.

What's the SAAMI .010" wall slop?

Never heard of that.

The die headspace I'm referring to is the distance from the shellholder base to die shoulder reference diameter when the die is touching the shellholder.

Forster hones their die neck diameter to the dimension customers want. Typically a thousandth or 2 less than loaded round neck diameter.

 

[Orange Dust]

Question, how do I determine "case neck clearance"? I don't have a copy of the blueprint for the reamer, it's a .270 AI, and getting a copy of the reamer blueprint is not an option as the gunsmith does not have one. Can the case neck clearance be determined from measuring a fired case?

Question has two answers. Do you want to know if you have "Enough" or exactly what it is? Finding out if you have "Enough" is easy. Just measure the neck of a case before and after firing. There is some spring back, but cloes enough for the most part. Otherwise you will have to have a chamber cast. Useful, but there is also some shrinkage.

 

[Alibiiv]

Question has two answers. Do you want to know if you have "Enough" or exactly what it is? Finding out if you have "Enough" is easy. Just measure the neck of a case before and after firing. There is some spring back, but cloes enough for the most part. Otherwise you will have to have a chamber cast. Useful, but there is also some shrinkage.

I'd just like to know if I have "enough" brass to be able to turn the necks without getting too much clearance. Was more concerned about spring and getting an accurate measurement. I'm just about barely skimming my brass now, but would like to be able to really clean up the brass without too much clearance and also maintain neck tension. Presently using Nosler .270 Winchester brass to fireform the .270AI, I will be going to Norma brass as soon as I can find some as it is either hit or miss with Norma.

 

[Mram10us]

What's the SAAMI .010" wall slop?

Never heard of that.

The die headspace I'm referring to is the distance from the shellholder base to die shoulder reference diameter when the die is touching the shellholder.

Forster hones their die neck diameter to the dimension customers want. Typically a thousandth or 2 less than loaded round neck diameter.

Here's an example of the difference in case wall measurement v chamber measurement. The saami prints I've used seems to be ~.001" difference.

edit! Sorry, I put .010" in the prior post!

 

[Bart B]

Question, how do I determine "case neck clearance"? I don't have a copy of the blueprint for the reamer, it's a .270 AI, and getting a copy of the reamer blueprint is not an option as the gunsmith does not have one. Can the case neck clearance be determined from measuring a fired case?

Yes, except fired case necks are often a thousandth or 2 smaller.

Use a hole micrometer to measure chamber neck diameter then subtract case neck diameter.

 

[Orange Dust]

I'd just like to know if I have "enough" brass to be able to turn the necks without getting too much clearance. Was more concerned about spring and getting an accurate measurement. I'm just about barely skimming my brass now, but would like to be able to really clean up the brass without too much clearance and also maintain neck tension. Presently using Nosler .270 Winchester brass to fireform the .270AI, I will be going to Norma brass as soon as I can find some as it is either hit or miss with Norma.

Don't take any more off than you have too or you will lose accuracy. Since you are turning necks measure fired/unfired. If you are .006 or more I wouldn't take any more off, even though they do look prettier if you do.

 

[Bart B]

Here's an example of the difference in case wall measurement v chamber measurement. The saami prints I've used seems to be ~.001" difference.
View attachment 168868
edit! Sorry, I put .010" in the prior post!

You're using the case and chamber body diameters?

Note the tolerances allowed will easily cause greater differences.

 

[Mram10us]

Yes. Are they honing case walls and neck? Shoulder is already adjustable.

 

[Bart B]

Yes. Are they honing case walls and neck? Shoulder is already adjustable.

Only the neck is enlarged.

Body diameters can be egg shaped and have uneven diameters but the case shoulder centers perfectly in the chamber shoulder aligning the case neck well centered in the chamber neck. No part of the body between shoulder and pressure ring touches the chamber when fired.

 

[Bart B]

If anyone thinks a 25 to 30 pound firing pin spring driving a 2 to 3 ounce firing pin near 20 fps won't force a 1 ounce cartridge to move a couple thousandths into the chamber shoulder denting the primer at least .015" to fire it should do their own tests. Cut one turn off the firing pin spring, load then fire a primed case. Cut off another turn then pop another primed case. Repeat until the spring is too weak to fire the primer. How deep does the pin dent that unfired primer?

If you measure case headspace before and after firing the primer, you should see how much case shoulder set back is from firing pin impact.

If you think the extractor holds case heads against bolt faces, remove the extractor then do this test.

 

[Mram10us]

Only the neck is enlarged.

Body diameters can be egg shaped and have uneven diameters but the case shoulder centers perfectly in the chamber shoulder aligning the case neck well centered in the chamber neck. No part of the body between shoulder and pressure ring touches the chamber when fired.

We need to start a thread for all this because I like the discussion but don't want to hijack the thread anymore than we already have sorry OP

 

[J E Custom]

Question, how do I determine "case neck clearance"? I don't have a copy of the blueprint for the reamer, it's a .270 AI, and getting a copy of the reamer blueprint is not an option as the gunsmith does not have one. Can the case neck clearance be determined from measuring a fired case?

Measure a fired case neck and then size and load it. then measure the loaded neck diameter to get the difference. The difference will be very close to the clearance depending on the pressure of the load. If you load concentric ammo 1/2 this dimension will be the clearance on each side. If you don't turn the brass and one side of the neck is thicker than the other, then the difference will be the overall clearance.

Example= if you have a neck thickness difference on one side of .002 and the total of .004 clearance you could be touching one side and have the total of .004 on the other side. This is still safe but it will offset the neck after firing.

This is the best way as far as I am concerned because this measures the actual chamber dimensions. With the SAMMI allowable's in the reamers, they can vary
A small amount and this assures that the dimensions are very close.

You have to depend on the reamer manufacture and the smith to get it right, But you also need to know what your chamber actually is.

J E CUSTOM