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

[fiftybmg]

If you've ever watched a bottleneck case neck position in the chamber neck, you'll notice it centers perfectly from ejector and firing pin force raising the case body off the chamber bottom when in the firing position with the case shoulder well centered in the chamber shoulder aligning the case neck in the chamber neck center.

You are saying that if you spray the loaded round with engineering marking blue and chamber it, it will be marked perfectly symmetrically along it's entire length.

Because it if doesn't, then it isn't.

 

[Bart B]

You are saying that if you spray the loaded round with engineering marking blue and chamber it, it will be marked perfectly symmetrically along it's entire length.

Because it if doesn't, then it isn't.

No, not saying that at all. The case is smaller than the chamber.

If there's an ejector in the bolt face, the case shoulder will be marked by the chamber shoulder.

If the extractor has to slip over the case rim, that'll also cause the case shoulder to be marked by the chamber shoulder as it's pressed into the chamber.

The case body will be marked wherever it slid against something on its way to being chambered.

If the case head is fit against the bolt face behind the extractor claw then chambered and there's no ejector pushing out of the bolt face, there usually won't be any touch marks on the case shoulder; if case headspace is less than chamber headspace.

 

[Rich Coyle]

Your ammo is not consistent when you neck size. /QUOTE]

Upon what do you base this proclamation? No ammo is consistant if one doesn't follow a good protocol.

 

[Rich Coyle]

I have a wildcat I named 6.5SLR for Sue loves Rich. That's what's on the reamer. What did he put on the barrel? 6.5 Coyle.

Ammo specs have a maximum and minimum dimension . So You cut a chamber to SAMMI specs, These dimensions are the standard for Ammo manufactures. They have Minimum and maximum Dimensions so they will chamber. Some ammo manufactures go with the minimum and others go with the maximum instead of the middle of the tolerance. This is why factory is so poor in many cases and so different batch to batch. As a builder I have to go with the SAMMI chamber dimension and let the loader adjust his ammo to suite him. Some want me to adjust the dimensions to suite there ammo but I cant take that liberty because if I/we did the same brand of ammo from a different batch could cause problems.

I have even seen factory ammo that would not fit a SAMMI chamber. Most of the time it is belted ammo and the belt wasn't machined to the correct dimensions. with shouldered cases even if it is to long as long as it is not to far out of spec. You can close the bolt on it. Also some military cartridge case are thicker and it is recommended that these necks are turned if you use them, unless you have a loose chamber that Is a SAMMI maximum. Chamber drawings are very useful to the re loader because he can decide if he wants everything tight (Close to minimum dimensions, or loose dimensions for semi auto's and easy feeding.

So keep in mind that the top drawing is for the AMMO and is for the ammo makers. The bottom drawing is for the reamer maker so That he cant go beyond these Dimensions and the smith and cannot confused or substituted one with the other.

The only time a reamer maker can deviate form the SAMMI dimensions is for wildcats (Anything that is not SAMMI specifications) and he has to mark the reamer with a different name or identify the change. The smith then has to mark the barrel with the name on the reamer so the owner cant wont get confused and place the wrong ammo in the weapon.

J E CUSTOM

 

[J E Custom]

I have a wildcat I named 6.5SLR for Sue loves Rich. That's what's on the reamer. What did he put on the barrel? 6.5 Coyle.

On wildcats, it is a decision that the smith should make after contacting the owner.
Any time I build a rifle that has to many changes to the chamber that would make it impossible to list the changes, I would identify it as a 6.5 Improved or as he did the person on the reamer drawing 6.5 Coyle. If it was built for someone, I would include there name or as you said Sue Loves Rich below the cartridge ID. Often the owner wants to make the rifle special and commemorates them in the barrel ID.

The main thing it to let people know that the chamber is NOT SAMMI. If it is a SAMMI Chamber, I simply place the persons commemoration below the chamber ID. I am not sure that there are any other 6.5 SLR so It may not cause a problem except someone else gets it (That Is not Likely that she would ever let it go) but stranger things have happened. So the smith should have ID'ed the barrel with what was own the reamer
because it should set it aside from the SAMMI spec.

Often I am ask to place a saying on the barrel and do so but the barrel ID still has the chamber designation on it. I built one for my brother in law that has 5.56 on one side of the barrel and "All gave some, Some gave All" (he is a Vietnam vet).

I am not sure how other Smiths handle this, But I will always identify the chamber for what it is Sammi or not, so it is very clear to the owners. I know if the rifle had a Sammi chamber you would not have gone to all the trouble and cost to have the reamer maker grind you another standard reamer for the chamber.

J E CUSTOM

 

[Alibiiv]

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

Thanks, got it! Makes sense and that's easy to do!

 

[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.

There is a way to get "Enough" to do what you want to do. If you neck down a larger round the neck thickness will increase. In other words it will be a little thicker if you start with .280 brass instead of .270. You can neck down '06 in 2-3 steps. Playing with this will allow you to fit the brass to your chamber if you want to go to the trouble.

 

[Alibiiv]

There is a way to get "Enough" to do what you want to do. If you neck down a larger round the neck thickness will increase. In other words it will be a little thicker if you start with .280 brass instead of .270. You can neck down '06 in 2-3 steps. Playing with this will allow you to fit the brass to your chamber if you want to go to the trouble.

Good idea and not it's not too much trouble. Thank you

 

[Orange Dust]

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

You said the exact same thing I did, but 'splained it better. Thank You.

 

[J E Custom]

You said the exact same thing I did, but 'splained it better. Thank You.

Sorry
I must have missed your post. Normally If I see a post that is pretty much like I would post I give them a like and move on.

J E CUSTOM

 

[keithcandler]

A lot of Sins are forgiven by a gunsmith that centers the bore to the .0001 in a high quality barrel that is uniform from end to end. Chamber in perfect alignment with the bore is worth good money.

A lot of the other stuff is just chasing rabbits.

 

[bigedp51]

The Rifleman's Journal
Germán A. Salazar

"a full-length sized case in which the neck is also fully sized. There is clearance at the neck and in the body of the case, the closest fit anywhere is the bullet in the throat. If the neck to bullet concentricity is good (although it needn't be perfect), then the bullet will find good alignment in the throat and the case body and neck will have minimal influence. Let's not forget that the base of the case is supported by the bolt face or the extractor to a certain degree as well; this is yet another influence on alignment. As you can see, there are several points from base to bullet that can have an effect. My procedure is to minimize the influence of those that I can control, namely the case body and neck, and let the alignment be dictated by the fit of the bullet in the throat and to some extent by the bolt's support of the base. Barring a seriously out of square case head, I don't think the bolt can have a negative effect on alignment, only a slightly positive effect from minimizing "case droop" in the chamber. Given that a resized case will usually have a maximum of 0.001" diametrical clearance at the web, this isn't much of a factor anyway.

In conclusion, I believe that allowing the bullet to find a relatively stress-free alignment in the throat by full length sizing (including the neck) and turning necks to enhance concentricity gives the bullet the best probability of a well-aligned start into the rifling."

 

[keithcandler]

Only if the chamber is not cocked going into the bore.

Full length sizing is the rage now. Full length sizing means different things to different people...advanced full length sizing vs partial full length sizing vs std full length sizers.

Advanced full length sizing is based on reamer design vs sizer design, including spring back. Pass the Zanex.

 

[Bart B]

Germán A. Salazar forgets to mention the primary case part that centers the cartridge neck in the chamber neck. If the case neck is centered on it. It's the closest fit anywhere and its not the bullet or case neck.

It's the case shoulder physically centered in touching the chamber shoulder. If the case neck is centered on the case shoulder, it's centered in the chamber neck. The bullet goes along with it.

His diametrical clearance at the case web is misleading because that part of the case in front of the extractor groove is typically pressed against the chamber wall by the spring loaded extractor. Which means the case is a tiny bit crooked in the chamber.