Neck tension and max bullet grip force

[nealm66]

I've also found weatherby calibers to like .003 to .004 tension better than .001, sometimes drastically. But I've always wondered why

I was told it helps because of the freebore and also to avoid a second detonation which can cause dangerous pressure.

 

[bedrok]

bedrok I have found the same thing!
My 300 weatherby mag will not shoot as tight groups as a lightly crimped round will so I bought a Lee Factory Crimp Die and put light crimps on necks.
I bet I can reduce my groups with a bushing die a little tighter or maybe that rifle just likes the Lee F C D.
Since you posted that point I have decided to increase the neck tension to about .004 and check groups.
All my other rifles shoot with .001-.002 neck tension but that 300 weatherby mag likes them a bit tighter it seems.
Thanks for confirming what I thought.
Old Rooster

I would opt for a smaller bushing rather than trying to crimp a non canalured bullet. I use Redding S bushing dies for all my rifles and have got the same or better accuracy with tighter necks in all of them. Years ago I would have expected the opposite. I'm trying to get a friends .300 Weatherby to shoot. Douglas moly barrel w .500 freebore, etc. Whoever did the barrel sucked. Factory cartridges have .033 headspace in front of them, the crown is rough, some other issues. I didn't have bushing dies so I honed the expander ball (originally .001 under) and accidentally made it .004 under by the time it was polished. In each of 4 loads, the tight necks shot groups 1/3 to 1/2 the size of the loose necks. Is the tight neck making up for out of concentricity issues in the chamber? Too dumb to figure it out.

 

[ntsqd]

It was called IF to start with and the slang term Neck Tesion caught on and took over

It is past time to start referring to it by its proper name again then.

As has been posted, increasing the Interference Fit beyond a relatively small change takes the brass into the yielding zone when seating the bullet and results in little to no increase in grip on the bullet. Adding a crimp sure will!

 

[nealm66]

I would opt for a smaller bushing rather than trying to crimp a non canalured bullet. I use Redding S bushing dies for all my rifles and have got the same or better accuracy with tighter necks in all of them. Years ago I would have expected the opposite. I'm trying to get a friends .300 Weatherby to shoot. Douglas moly barrel w .500 freebore, etc. Whoever did the barrel sucked. Factory cartridges have .033 headspace in front of them, the crown is rough, some other issues. I didn't have bushing dies so I honed the expander ball (originally .001 under) and accidentally made it .004 under by the time it was polished. In each of 4 loads, the tight necks shot groups 1/3 to 1/2 the size of the loose necks. Is the tight neck making up for out of concentricity issues in the chamber? Too dumb to figure it out.

I've been told to avoid bushing dies unless you're neck turning or using very high quality brass. I am able to get very good results with good quality fl size dies with the expander ball and amp annealing.

 

[ButterBean]

It is past time to start referring to it by its proper name again then.

As has been posted, increasing the Interference Fit beyond a relatively small change takes the brass into the yielding zone when seating the bullet and results in little to no increase in grip on the bullet. Adding a crimp sure will!

I'm all for it

 

[bedrok]

I've been told to avoid bushing dies unless you're neck turning or using very high quality brass. I am able to get very good results with good quality fl size dies with the expander ball and amp annealing.

I always turn the necks, although with Norma or Lapua it wouldn't be necessary. I didn't turn necks for The weatherby In question, but they were surprisingly concentric.

 

[ntsqd]

I'm probably missing some nuance, but I don't see a reason to not use bushing dies if the ability to tune the neck OD prior to expanding is important to the situation. High or low quality brass wouldn't matter at this step, but it will at the next step; neck expansion.

Reloading at this level just about requires the purchase of a tube wall thickness micrometer, or one of the reloading specific tools that do the same thing, so that neck wall thickness can be checked.

I've been told to avoid bushing dies unless you're neck turning or using very high quality brass. I am able to get very good results with good quality fl size dies with the expander ball and amp annealing.

 

[Mikecr]

If you're getting good results with FL sizing of necks, then there is reason to consider as good or better results with partial length bushing sizing and the right powder. The LENGTH of interference can be adjusted with a bushing die to tweak tension while avoiding sizing/bringing donut into tension.
With this, tension variance will be greatly reduced.
There is no reason to overwork necks with this. Just size down enough to get a good mandrel pre-seating, for a length of that sizing that never exceeds seated bullet bearing.
Bullet grip will be spring back force X area of bearing gripped. PSI

Sizing length beyond seated bearing leads to a binding tension on the bearing-base junction. That's a lot more tension, and tension variance, do to bringing so much more into tension that is not as well controlled. Donut area, and shoulders.
If you're finding better results during development with an extreme sizing here -then you need to move to a faster powder that still fills the case at SAAMI max pressures. Get back to rational and lasting reloading.

If missing info to do so, dump the manuals(all of them) and get QuickLoad.

 

[Old Rooster]

bedrok I use only Redding Bushing Dies for most of my rifles and recently bought a Mandrel for 30 cal to push the neck irregularities to the outside.
I haven't gotten Bushing Dies for 270 or 358 win as I don't shoot them much and later I will get Bushing Dies for them.
The bullet setback is my main concern and 180 gr bullets have less setback that 212 ELD-X.
I know better Brass will help my problem but there is none anywhere at any price.

 

[QuietTexan]

Just to loop that back to practical for a minute, what I'm reading here is that if someone wanted to mandrel size as the final step before seating, this would be a functional sizing process without excessive steps to test:

1. Bushing size at 0.001-0.003" smaller than as-fired
2. Mandrel expand to 0.0020"-0.0005" under caliber

Also there's the assumption you're doing this on quality brass that has less than 0.0015" variation with a neck thickness of 0.012-0.015".

With good measuring you could likely rule out certain combinations from the get go, ie (using 30 cal for a very contrived example) a 0.3075" mandrel won't actually expand 0.012" turned brass sized with a .337" bushing because the neck won't have been sized down enough to touch the mandrel. You'd need a 0.331" bushing to get that brass tight enough for a mandrel to touch it.... and a shrink to help you figure out with why you have such thin necks in such a loose chamber.

21st sells mandrels in 0.0005" increments:

Caliber Specific Expander Mandrel Kits

Our caliber specific expander mandrels are available in .0005” increments in calibers 22 to 338 and will range from .001” above bullet diameter to at least .003” below bullet diameter depending on caliber. This will allow the reloader to find proper neck tension to fine-tune their loads. The...

21stcenturyinnovation.com

Then for someone who wants to jostle the cartridges and hunt with these very delicately sized rounds, use an FCD as a final tune.

 

[Old Rooster]

QuiteTexan I use a .330 neck bushing but as ntsqd said I won't gain anything as spring back will only allow a minimal interference fit so I am going to continue with my Factory Crimp Die with this brass to stop bullet setback in rounds in the magazine on this 300 weatherby mag.But I do have a .331 bushing.
I will be looking to buy better brass when the shortage ends,if it ever ends.
I remember you were the one to coach me on fine tuning my FCD and that's why I get good groups but the problem is that I have no way to see how much crimp I am getting.So when I can get quality brass I will try my Redding Bushing Die with a neck bushing I will figure out when I get my quality brass.
I'll look to see if I still get bullet setback and if I do I will continue with FCD.
Thanks
Old Rooster

 

[Bob Wright]

The biggest problem is variables in brass and prep. Therefore there is no clear cut way to do a calculation with 2 or more variables. Just prep your brass the same way, and then experiment with one thing at a time. The goal is to get a minimum sample size, like 10, and measure velocity variation. Try something else in a logical manner to see if variation gets smaller. I cannot see putting all this thru a math analysis and getting a meaningfull result. It simply needs careful consistent brass prep and trying incremental documented steps to improve.
I have 40 years in aero engineering. There is little that calculations can do to solve the myriad variations except bench experiments, consistent prep and chronograph results. It's more old school basic approaches as much as I hate to admit it. Once you master one chambering, you have a good foundation and start point for all others.

 

[Old Rooster]

Makes a ton of sense Bob and thanks.
When better brass is available I will get it and just maybe some of the variables will disappear I hope.
When it comes to 300 weatherby mag brass you have to get what you can find.
I am getting less than 1/2 inch groups right now,didn't have my tape or calipers so I'm guessing but had previous targets with measured groups to compare.
Thanks again
Old Rooster

 

[ntsqd]

So my Multi-variable Calculus class was the waste of time that I thought it was? Yea! Hated it!

Big factor in crimping will be case length variance. Even a tiny difference in length will have a large effect. Next will be needing a positive stop of some type. Though other may differ, I don't think that "cam-over" is consistent enough. In various operations that I've set up to 'cam-over' in the past I could feel a difference from one case to the next.

Used to be that Weatherby sourced his brass from Norma. I assume that this is still the case? If so, finding quality brass isn't the problem. Finding brass at all is the problem.

I've long wondered about sourcing or making cases with a deliberately slightly thick neck, just so they could be turned to the nominal size (to fit & function a std. SAMMI chamber) and not be an interrupted cut. An interrupted cut would mean non-uniform thin spots in the neck.