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

Bart B

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Does one method end up with bullets better centered in the bore when fired? If so, why?
 

J E Custom

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Does one method end up with bullets better centered in the bore when fired? If so, why?

In my opinion Yes.
But there is more to centering the bullet than just neck sizing. cases need to be prepped and turned before they are ever fired. Then with minimum sizing or Neck sizing the chamber will hold the cartridge in perfect alignment. The concentricity of the loaded ammo also has a bearing on centering the bullet.

So keep In mind that one or the other method may not be any better if all the other conditions are not dealt with.

J E CUSTOM
 

Orange Dust

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In my opinion Yes.
But there is more to centering the bullet than just neck sizing. cases need to be prepped and turned before they are ever fired. Then with minimum sizing or Neck sizing the chamber will hold the cartridge in perfect alignment. The concentricity of the loaded ammo also has a bearing on centering the bullet.

So keep In mind that one or the other method may not be any better if all the other conditions are not dealt with.

J E CUSTOM
THIS... AND to back up what he said, if you don't skim turn and square up the necks to true them, I don't feel either method has any effect on accuracy whatsoever as long as they are sized properly. In fact, there is a faction that believes if you don't prep your brass you are actually better off using small base dies and completely sizing cases back to nearly new factory dimensions. They feel this allows the case to self align in the chamber somewhat, like a factory round. For our purposes (a long range precision rifle) I feel very strongly every round of brass should be fully prepped and sorted. Great loads cannot be either consistent, or duplicated without this step. Leave this step out and you will always be chasing your tail for accuracy. You can find a load that shoots the magic 1/4" group. Go home and load up a bunch and the next group just may be 1-1/4". Doesn't take long to turn, trim and chamfur the necks, ream the flash holes and primer pockets on 100 cases. Doesn't take long to sort them by weight either. I don't sort them until they have been fully prepped.
 

Mram10us

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From a hunting stand point I always full length, just do not want to risk a loading problem. I never jam the bullet either. If I was a target guy would likely neck size.
Most target guys FL size now days.

It seems neck sized would line up better because the .010” of slop from case walls to chamber wall would be taken out. It doesn’t seem to improve accuracy.
 

Bart B

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Where is a rimless bottleneck cartridge in the chamber when the primer fires?

A. Held against the bolt face by the extractor.

B. Resting on the chamber bottom.

C. Pushed into the chamber shoulder by the firing pin. And the bolt face ejector, if used.
 

Mram10us

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Where is a rimless bottleneck cartridge in the chamber when the primer fires?

A. Held against the bolt face by the extractor.

B. Resting on the chamber bottom.

C. Pushed into the chamber shoulder by the firing pin. And the bolt face ejector, if used.
I’m interested in the point you’re getting at :)
 

Mram10us

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Where is a rimless bottleneck cartridge in the chamber when the primer fires?

A. Held against the bolt face by the extractor.

B. Resting on the chamber bottom.

C. Pushed into the chamber shoulder by the firing pin. And the bolt face ejector, if used.
Assuming headspace is correct, the shoulder of the case is slightly wedged in the chamber. neck has slop. case body has slop. To me, it seems the most important part is the face of the shoulder having light contact with the chamber.

Walls will have .010” ish slop
Neck will have .002” ish depending on how much you turn
Shoulder should have .002” if that is how you resize.
Check my numbers though
 

J E Custom

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Most target guys FL size now days.

It seems neck sized would line up better because the .010” of slop from case walls to chamber wall would be taken out. It doesn’t seem to improve accuracy.

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
 

Bart B

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Assuming headspace is correct, the shoulder of the case is slightly wedged in the chamber. neck has slop. case body has slop.

Walls will have .010” ish slop
I think a 2 to 3 ounce firing pin pushed near 20 fps by a 25 pound spring force would very tightly press the case shoulder into the chamber shoulder. Sometimes setting the case shoulder back a couple thousandths.

Is the back of the chambered case body ever pushed against the chamber by the extractor claw?
 
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Orange Dust

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Ok guys, after reading this thread, you may be scratching your head and wondering if all the trouble JE and I are talking about is worth it. I will assure you it is not necessary if you want to shoot game at 400yds or less. If you want to shoot far it absolutely is. Allow me to share a story with you. The other day a friend of mine missed a deer. He asked me to go with him to check his rifle. He shoots a shelf rifle with factory loads from Wal-Mart. I loaded everything in the SxS and we went to where we have a range set up on our place. I put my rifle in since deer season was open. We sighted in his rifle without incident. He said "lets see you shoot that fancy rifle with those reloads you shoot". I said "ok, put up a clean target. He did, and I told him to get in the SxS. Started driving back toward camp. Went across the field we were in and kept going. When we got half way across the next one he asked if I was going to shoot or if I was chicken. I stopped, and ranged the target. 597. He said he couldn't even see it. Got my rifle, and down on my belly. Wind was 1mph right to left. I dialed 1.5Mils U and .1Mils R and let one fly. Then another. We drove back to the target and all he had to say was "Can you teach me?".
28N 600yd (600x800).jpg
I explained to him that the fact they hit right beside each other was irrelevant. What matters is the vertical. I would have also been happy if they had been 2-3" apart with no vertical. This is a good load. Once I finish load development in a hunting rifle I don't shoot groups any more with that load. Just a cold bore and a follow up. Target is 1" squares, and his rifle does not shoot this well @100. He was utterly amazed. I told him it is really no big deal, and not really that hard to do. It does take patience and attention to detail.
 
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