Neck tension starting point

[dellet]

You generally don't. You don't crimp for accurate rifles, and it doesn't matter for the ones you do crimp (lever actions, etc).

Are you saying Mil Spec ammo and rifles aren't accurate?

 

[dcali]

Are you saying Mil Spec ammo and rifles aren't accurate?

Yes, by my definition. By "accurate", I mean something comparable to benchrest, f class, or high end varmint rifles - something capable of repeatable sub 1/2 MOA precision. Military rifles and ammunition, in general, don't meet that bar. Neck tension is not a factor when bullets are of poor quality and rifles are designed for fighting, serviceability and cost. It just doesn't matter.

 

[fguffey]

What is the proper unit of measure for “tensions”?

What is the unit of measure for tensions? I do not have a conversion chart of tensions to pounds, I have tensions gages that measure in pounds but I find it impossible to convert tensions to pounds. The first tension gage I saw was overhead, I was working on the floor of a triple. At the time it seemed important to know how much weight was supported by all of the cables hanging from the top of the rig. I was impressed when I was told we had to multiply the indicated weight by the number of cables. I was 15 at the time.

Tensions is a cute term that is used by reloaders when they do not understand what is going on, something like 'fire form', I chamber a round, pull the trigger and then eject a fired case, reloaders pull the trigger and then become 'fire formers'. I form first and then fire.

F. Guffey

 

[dellet]

Yes, by my definition. By "accurate", I mean something comparable to benchrest, f class, or high end varmint rifles - something capable of repeatable sub 1/2 MOA precision. Military rifles and ammunition, in general, don't meet that bar. Neck tension is not a factor when bullets are of poor quality and rifles are designed for fighting, serviceability and cost. It just doesn't matter.

So if I aspire to have ammo better than 2 MOA, which I think is Mil Spec, I might want to look elsewhere for for loading tips?

If I start at .002", what am I looking for that says I need to try something else?

 

[Bart B.]

So since the talk has turned to Mil spec and or commercial standards for the amount of pressure to start a bullet moving. Arguing to use that as the gold standard.

How do you factor in the crimp?

One way to see the crimp factor is comparing bullet extraction force specs for 7.62 NATO M118LR and M80 ammo; only M80 ammo is crimped. Their bullets have about the same clearance to case necks and use the same sealant.

M118LR, 20 pounds minimum.
M80, 60 pounds minimum.

 

[fguffey]

And then there was the older shooter that was handed a rifle and ammunition at the contest; he came to the shoot without a rifle. He requested another rifle because the rifles available at the contest 'just would not shoot'. They took him to an armory, he picked a rack rifle and returned. With the rack rifle he scared a few and made the trip worth while for all the rest in attendance. The point? They did not give him different ammo, he used the same ammo with a different rifle.

F. Guffey

 

[dellet]

One way to see the crimp factor is comparing bullet extraction force specs for 7.62 NATO M118LR and M80 ammo; only M80 ammo is crimped. Their bullets have about the same clearance to case necks and use the same sealant.

M118LR, 20 pounds minimum.
M80, 60 pounds minimum.

And how exactly does that relate to repeatable performance?

 

[Bart B.]

From Lake City ammo plant, 7,62 NATO M118LR specs,

BULLET: 175 gr Sierra HPMK, Reverse Drawn Copper Jacket with Boat-Tail and Lead Core

VELOCITY: 2,575 ± 30 ft/sec (78 ft from muzzle)

ACCURACY: Average horizontal and vertical standard deviation maximum:
Horizontal: 10.3 in @ 1000 yds)
Vertical: 14.0 in @ 1000 yds)
- or -
Horizontal: 1.3 in @ 200 yds)
Vertical: 1.5 in @ 200 yds)

Tested with match grade barrels in bolt actions

Extreme spread is 2 to 3 times standard deviations.

 

[UltraBR30]

What is the unit of measure for tensions?

The unit of measure for neck tension is Inches.
SAAMI definition for Neck Tension:
The circumferential stress that the case neck exerts on the seated bullet, as a result of the interference fit provided by the case neck inside diameter and the bullet outside diameter.

It don't get much simpler
Phil

 

[Bart B.]

And how exactly does that relate to repeatable performance?

Consider how the bullet pull force can change muzzle velocity spread if each has a 30% spread.

Then drop extraction forces down to 3 and 9 pounds and use the same 30% spread.

 

[dcali]

So if I aspire to have ammo better than 2 MOA, which I think is Mil Spec, I might want to look elsewhere for for loading tips?

If I start at .002", what am I looking for that says I need to try something else?

To do better than 2 MOA, you need two things. One is a rifle that is capable of it. In my experience, an off the shelf AR or M1A is sufficient. A typical AK is not. The second is good bullets. Military style fmj’s wont hack it in general. You need match grade HPBTs like Sierra matchkings. At that point you’ve done just about as much as you can do, although you might make further gains but testing charge weights and seating depths (if the rifle will allow for it). The finer points of reloading are wasted effort when you’re dealing with military grade weapons.

 

[BoydAllen]

A neck tension story: A while back I was helping a shooter get started with a 6PPC. He had bought a large amount of LT32 and in our discussion I asked him how much neck tension he was using, which turned out to be what I thought more appropriate for 133 than LT32. I suggested that he reduce his neck tension and his groups improved. My point is that different powders can have different neck tension "preferences".

In the past, when I was loading at a match, seating bullets with an arbor press, if I noticed differences in the effort required to seat bullets, I would group loaded rounds in as many as three groups and try to use those with the same feel on the same target. If there were only a couple that felt strange, I would use them for after cleaning foulers. In this sport scientific proof can be hard to come by.

 

[Bart B.]

To do better than 2 MOA, you need two things. One is a rifle that is capable of it. In my experience, an off the shelf AR or M1A is sufficient. A typical AK is not. The second is good bullets. Military style fmj’s wont hack it in general. You need match grade HPBTs like Sierra matchkings.

The best rebuilt M1 and M14 service match grade rifles would shoot 7.62 M118 match ammo rebulleted with Sierra 180 HPMK'S that tested well under MOA at 600 yards; about MOA at 1000. Those military 173 grain FMJBT match bullets were not so good.

The US Army's rebuilt AR10's shot in the 2012 Nationals 1000 yard service rifle matches did somewhat better shooting Berger 185 VLD'S.

 

[dellet]

A neck tension story: A while back I was helping a shooter get started with a 6PPC. He had bought a large amount of LT32 and in our discussion I asked him how much neck tension he was using, which turned out to be what I thought more appropriate for 133 than LT32. I suggested that he reduce his neck tension and his groups improved. My point is that different powders can have different neck tension "preferences".

In the past, when I was loading at a match, seating bullets with an arbor press, if I noticed differences in the effort required to seat bullets, I would group loaded rounds in as many as three groups and try to use those with the same feel on the same target. If there were only a couple that felt strange, I would use them for after cleaning foulers. In this sport scientific proof can be hard to come by.

If I understand this correctly.

Changing neck tension, defined in this purpose as the amount of force needed to overcome the hold the neck of the case has on the bullet, can influence the burn rate of the powder.

If this is true, all other factors such as neck, body, headspace, and bullet jump clearances as well as load density, will also need to be factored in, because the rate and efficiency the gasses expand, is determined by how tightly they are contained.

Could this be the reason why trying to assign a certain number or formula to compensate for an almost endless number of variables is basically pointless?

The OP asked for a good place to start, .002" sure seemed to come up a lot. One bushing either way will probably just about cover every number thrown out there. My guess is he'll probably need to try a 4th just to make sure he has it all covered.

Probably why most answers to load questions should start with;
"It depends on...."

 

[ClassCat]

Mhmmmmm - I was looking forward to seeing a target ............. We've worn neck-tension and a few other thing right out..........

There's one I shot @ 200 yds. with .003 neck tension at this link (the 28 Nosler) http://forum.accurateshooter.com/threads/official-gun-pix-pride-joy-thread.2990828/page-25

Impressive ! What did the first 5 look like ?

 

[fguffey]

The unit of measure for neck tension is Inches.

I own tension gages, my tension gages do not measure in inches, my tension gages measure in pounds. I have deflection gages, my deflection gages measure in inches with a plus, the gages measure in deflection + the number of pounds required for the amount of deflection.

F. Guffey

 

[Bart B.]

The unit of measure for neck tension is Inches.
SAAMI definition for Neck Tension:
The circumferential stress that the case neck exerts on the seated bullet, as a result of the interference fit provided by the case neck inside diameter and the bullet outside diameter.

It don't get much simpler

That's good info, but it brings up this question.

With two cases resized to have a .002" interference fit, one with .006" thick neck wall and the other .012" thick, will the circumferential stress case necks put on bullets be the same for each?

 

[rebel]

 

[Drop Port]

In the end it's all SWAG. I can tell you my neck ID my bullet OD and type of lube or not and in the end it doesn't amount to a hill of beans from one rifle to the next. All I know is what works for me in two of my rifle are at opposite ends of the spectrum. Tune it to what works.

 

[LA50SHOOTER]

Impressive ! What did the first 5 look like ?

I’d estimate in the high 1,s or low 2’s from what I can remember, it was still looking real good still at 10 shots and the barrel wasn’t hardly warm so I continued firing on it. Benchmark makes a good barrel I believe.

Regards, -Ron-