Formula for correct neck tension.

[halfmoanut]

If my brass is neck turned to 8.5 per side and my bullets are 243.3 on the pressure ring what formula is used to obtain .003 thou of neck tension on this bullet? And .001 thou of spring back which is considered by most die makers. TYK.

 

[243winxb]

.257" & .256" bushings. Simple math. Get more opinions. I only have so many fingers to count with.

I thought neck walls should not be thinner then .010" ? Just asking.

 

[Jet]

Load a round in your case and measure the outside diameter then subtract .003 for the bushing to use.

Assuming your loaded outside neck diameter will be 260.3 I would test various bushings from .256-.259. I've found the proper neck tension to use is not set in stone and should be part of your load development. Powders respond to neck tension differently.

Good shooting

Rich

 

[Jet]

.257" & .256" bushings. Simple math. Get more opinions. I only have so many fingers to count with.

I thought neck walls should not be thinner then .010" ? Just asking.

My guess would be HALFMOANUT is shooting a 6PPC with a .262 neck.

 

[butchlambert]

All calibers and ammo do not necessarily shoot best with the same neck tension. Powder burn characteristics effect the required neck tension.

 

[arm017]

All calibers and ammo do not necessarily shoot best with the same neck tension. Powder burn characteristics effect the required neck tension.

Would you say you have found any rough rule of thumbs in this regard Butch? IE: faster burning powder for caliber do better with more/ less neck tension?

 

[divingin]

If my brass is neck turned to 8.5 per side and my bullets are 243.3 on the pressure ring what formula is used to obtain .003 thou of neck tension on this bullet? And .001 thou of spring back which is considered by most die makers. TYK.

.2433 + .0085 +.0085 = .2603 Loaded neck diameter

subtract .003 for desired neck tension, then subtract another thou for springback

.260 - .004 = .256 bushing

Or .257 if I misinterpreted and you already allowed for the springback and wanted .002 neck tension.

 

[mikecr]

You didn't say whether bushing/partial sizing or FL neck sizing.
Big difference to consider here.

 

[butchlambert]

Would you say you have found any rough rule of thumbs in this regard Butch? IE: faster burning powder for caliber do better with more/ less neck tension?

Well, a lot of us have found that 133 likes more neck tension to help it build a little more initial pressure and the old H322 liked light neck tension.

 

[gpoldblue]

Amen Brother.

Every barrel/chamber is different, that's why testing, testing, testing is necessary to find what works for your rifle.

Here is where a chronograph can be used effectively. By changing neck tension,you may be able to lower ES/SD without sacrificing accuracy......
may actually improve.

 

[BoydAllen]

For me, the whole point of bushing dies is to be able to experiment with different bushings, so I would suggest that you buy several sizes, .256, 257, and .258. I prefer Wilson bushings because they give an additional .0005 of sizing when they are flipped over. As to spring back I am not so sure about that. Lacking the tools to do accurate bushing ID measurements, I used to think that the difference between what the bushings were marked and the diameters of sized necks to be due to that, until I acquired a carbide bushing. They are ground instead of being turned and polished, and the ODs of the necks sized with it were pretty much spot on. Before you rush out and invest in carbide, consider how well shooters have done before they became available. Sometimes we can become obsessed with the perfection of something that we have the means to measure, even though we cannot see a difference on our targets. As I have written many times, test and believe your targets, rather than your assumptions.

Added a little later: Although adding up dimensions will get you close, after you get a dummy round loaded, with the bullet you are using, you should measure the OD of the neck over the bullet's pressure ring, with a 1" micrometer that reads to .0001. This is work for a micrometer, not a digital caliper.

 

[T-shooter]

You may have to experiment because springback will vary due to various reasons. Different brass alloys and different states of annealing will change it. Also, to some degree, how long the case neck is in the die when it's resized.