.001 neck tension for .308 F-TR load?

[riflewoman]

A question if I may...what happens after the yield point has been reached ? I expand up about 0.004 on past advice this is required to break the yield point.

Yield point of brass. Interesting.

From Olin Brass.

A test by other, using a automotive valve spring test device of some sort.View attachment 1054897 See page #2 https://www.handloadersbench.com/fo...h-com-load-data/27215-neck-tension-experiment

From my “back of the envelope” analysis, a .001 on a .334 neck is about .003 stretch of the case. The analysis is hoop tension but if we assume this to be elastic stress, we can use the equation
€ = s/E x L; € = .003, s = applied stress, E = 16,000,000 psi/ inch/inch

In this case .334 is near enough to 1 inch and L is the elingation here .003 (.001 x pi)? So knowing all that we get roughly 45,000 psi applied stress. The only brass capable of that is H01 and H02 is 1/4 hard.

Once you pass the yield the brass will return to the diameter that will allow the stress to be roughly zero. In the case of soft fully annealed brass that would be a diameter ,0003 smaller than the loaded round. Good luck measuring that even with a tenth indicating micrometer.

 

[hunter243sgk]

It depends for me. I use different amounts as needed. For example I use way more for my ar than I do a bolt gun. Then I don’t have to crimp. And some bullets like more than others. It all depends on what I am using and in what I am using it in!!

 

[Martin52]

.....Once you pass the yield the brass will return to the diameter that will allow the stress to be roughly zero.

For bullet seating consistency then, is it better to expand the neck sufficiently to pass the yield, because the stress will be roughly zero ?

 

[Dusty Stevens]

If your using Wilson bushing they say you can flip it over put the numbers down and get another 1/2 thousand or so hold.
J

That would mean your bushing is tapered and you need to replace it

 

[cw308]

Very interesting reading . I'm not in the same league as you all but my thinking is the same . I'm shooting 308 , my groups are 1/2 inch at 200 yards not 600 , that's amazing . I use to use the same brass until I saw a problem then dump them all , average 23 reloads . This season I'm trying 3 different lots 30 each , nothing fancy , HSM ,FC and ADI . I don't neck turn or add heat to the brass . I'm wet tumbling now brass comes out like new every time , add Imperial dry graphite lube to the bullet when seating . So far the case strength or the lubed seating is making a difference for the better . I was going down that road like you all but I don't think I'm capable of shooting those micro groups . I stopped over thinking kept it simple for my ability but love reading about what the real tight groupers do . Great Reading , thank you all.

Chris

 

[riflewoman]

For bullet seating consistency then, is it better to expand the neck sufficiently to pass the yield, because the stress will be roughly zero ?

If neck tension from expansion is the sole parameter in bullet pull (and that has not been determined) then a soft un-cold worked neck will only give the tension up to the elastic limit of the material. It is not zero. How consistent it is will depend on factors some of which are beyond your control. Those will be metallurgical like grain size and size distribution, residual dislocations and slip planes, etc. With a full anneal including recrystallization, all of these factors are altered. If the brass has been segregated, sized carefully etc., the theory says that the bullet pull will be consistent in that batch of brass throughout its lifespan. This is probably why Brian Litz found no difference in his annealing test.

 

[Alex Wheeler]

Show up to deep creek on a testing day. Big difference at 1k in annealing vs unannealed. Also big difference in a bushing size even past the yield point.

 

[Bart B.]

I'm shooting 308 , my groups are 1/2 inch at 200 yards not 600 , that's amazing . I

I agree, that 1/4th MOA size for all groups is phenomenal.

 

[dcali]

I use roughly .001 for my TR loads, and it's working very well for me. You have to be careful because the bushings don't necessarily size to what is stamped on them. And if you're going to use tension on the low side, it's wise to turn necks, since they can vary by .001 of thickness in the same box.

As for yielding the neck, that happens quickly. Almost instantly if you anneal thorougly.

I did some thinking on that topic and came up with this:

https://bisonballistics.com/articles/case-neck-tension-a-stress-analysis

I personally do not anneal, and have not noticed that it's hurting me. Letting the brass harden and using a light (non-yielding) neck tension would in theory give you a pretty consistent grip, as demonstrated in the above link. But there are limits to theory. It is, however, exactly what I do, and it seems to work.

 

[cw308]

I tried bushing dies my runout was horrible went back to FL sizing die with .001 case headspace using competition shell holders set of 5 by Redding worked much better . What type of dies are you using . What is your setup . I use a single stage RochChuckrer . My die is nothing fancy RCBS FL die , shell holders an seat with Redding Competition Seating die . That's what I use . I'm not turning my beass , using the expander ball . Sizing is smooth I uniform my primer pockets , deburr the flash hole on the inside , trim an chamfer every firing . Fire one case brand at a time . Weigh my charge with the ChargeMaster 1500 then dump that into the pan on the GemPro250 to 40.82 grains of IMR 4064 under a 168 gr SMK. No need for speed , max. range is 200yards for the ranges in my area .

 

[dcali]

It might blow some minds,but in my most accurate and winning 308 barrel, 0.007 interference fit was the most accurate. Not only did I validate this multiple times, but it continues to shoot lights out after 3050 rounds. I have some theories about this, but the target has the final say. Drew

This is pretty interesting. That's well into yielding territory. I'm not sure how to explain why .007 would be much different than, say, .004-5. Did you test those as well?

 

[Alex Wheeler]

Neck tension is a weird area of reloading where people like to come up with theories on what should work and why, then stick with it. While in other areas like powder charge, we all just test it until you find the right place. I recommend treating neck tension the same way.

 

[skiutah02]

This is pretty interesting. That's well into yielding territory. I'm not sure how to explain why .007 would be much different than, say, .004-5. Did you test those as well?

Yep tested 0.002, 0.003, 005 and 0.007 at 100y, 300m 600y and 1000y. Repeated at 300m 600 and 1000 at least 1 more time on diff day w diff conditions. Vert shrunk with more tension every time. Don't have a bushing for 0.007+...

 

[riflewoman]

Alex/ Riflewoman
How much neck tension do you run on your 6 mm competition ammunition ?
Jim

I dunno. I load and shoot 6PPC and 6BR only for short range BR at the moment. I don’t worry too much as the brass gets worked so little.

However, I did load a lot for shooting an M1A over the course. I didn’t worry about annealing but I might start because LC Match brass is now unobtanium. It’s just that the current techniques used in these fancy annealing machines seem off. And I’m still not convinced they really make a more consistent product.

 

[Jdne5b]

Yep tested 0.002, 0.003, 005 and 0.007 at 100y, 300m 600y and 1000y. Repeated at 300m 600 and 1000 at least 1 more time on diff day w diff conditions. Vert shrunk with more tension every time. Don't have a bushing for 0.007+...

Drew just needs enough room to get the boat tail started. Then fully seats with a wilson die and 3lb hammer.

 

[calgarycanada]

Member of Canadian national team once told me he runs 5 thou neck tension, when I asked him how he keeps his vertical so small.

 

[Toejoe12]

A great benefit in the shooting sports gaining popularity in the last decade is the onset of better/different equipment and technology. This in my opinion has brought more great minds into our sport, many are on this site. It has opened the door to new ideas, old ideas with different twists, and old ideas with better equipment (again my opinion). I am a tester and enjoy doing it almost as much as competing. As many veterans of this site often advise........go out and test. I do! I'm fortunate to be close to a 500 yd range and frequent often as well as several close friends that share my passion. We share openly "information" as we are a team.

One of the areas we've spent significant time testing is brass prep and the MANY variables involved that lead to consistency in each loaded round. My/our experience is consistent neck tension is paramount to precision accuracy and will definitely become more and more obvious as you move back in distance. At 1000 yds it is an absolute must if you want to be competitive where precision counts.

The newer versions of arbor presses with pressure measurements combined with custom fit dies made measuring neck tension, friction, force fit..... etc using bushings (a tried and trued proven method so I'm not putting it down), some what out dated to the tools we now have easily available (again opinion). I have not used bushings in the last 1.5 years. My preferred method is running a certain size mandrel through the neck last. This does many things but the 2 most important I feel is controls "precisely" the neck size as well as ensures the "inside" of the neck is perfectly concentric. I had a mandrel die made that holds a collet, that holds a pin. Got the info and die maker info off this site. The pins I use are Vermont pin gauge easily purchased in the size(s) needed from Amazon for $7 each. If you're extremely anal you can pay $20 and order direct from VT Gauge and get a certified pin with in 1/10000 of an inch. Amazon offers in .0005 increments or if you want even more choices from Amazon, 7.80mm = .3071 and 7.81mm = .3074. After countless testing of different scenarios processes and even the order of steps within the different processes (there could be a book written on this alone) my/our current process is a variation of the below.

• Nk turn brass to desired nk wall thickness
• Clean brass or wipe down, whatever you prefer. Haven't found this much matters as nk tension can be controlled by mandrel size
• Anneal after every firing.......easy as I have an annealer
• F/L size (no bushing)...I had a die made to my chamber specs that size the neck down .0025 from fired case neck size
• Open neck back up minimally with correct size mandrel pin referenced above.
• Tumble in corn cob for 30 min to get whatever brand lube you use off case
• Trim or chamfer to my preferred specs if needed
• Prime and drop powder
• Seat bullet with another custom seating die I had a good friend make from the chamber of one of my shot out barrels....no better fit than that
• Use arbor press with psi measurement to seat. (I prefer between 30 psi and 50psi tension/fit) *

*Note: 30 to 50 is an over all range of comfort I have on the measurement. The lots of match brass I load will all be within 2 to 4 psi range of one another. Example: a complete match set....22 rounds including sighters will be 30 psi to 34 psi. Another match set of 22 could be 44 to 48 for all 22. Doesn't matter to me as long as they all are within my tolerances for the 22 set and fall with in what I deemed the sweet spot listed on the last bullet point above.
I have my brass in lots of 75 for a full match and 90% of the lots fall in the 35 to 40 psi range. I have no idea what that translates into inch measurement fit/tension. It's just a different process and measurement I feel is more precise.

A version of the above process has been very successful the last year and a half for the core guys I shoot with constantly.

Sorry for the long response but I'm on vacation and a bit bored and thought I would give a different perspective.

 

[Alex Wheeler]

Heres a few targets I shot while tuning up a 7saum hunting rifle #4 contour barrel. I shot these all at 1k in the middle of the day. Not the best groups in the world but OK for a hunting rifle. No turn brass with .005" neck tension. I would expect much better in a target rifle, but Ive never been able to shoot a hunting rifle much better than 3-4" at 1k.

 

[dcali]

Drew just needs enough room to get the boat tail started. Then fully seats with a wilson die and 3lb hammer.

I might try seating some 7mm bullets in some 6.5-284 brass. Necking up is for suckers.

 

[cw308]

Toejoe12
Thank you , great read . Sharing information to help each other is what this forum is about . Last year at the range a few benches down from mine ,this guy was shooting reloads in 308 , to make conversation at a cease fire time , l said your reloading 308 he said yes . I asked what powder , charge an bullet are you shooting . He said , I'm not telling you my information , you wouldn't tell me yours . He cought me so off guard I just said ,WHAT . I guess in not such a nice way . Then said I have no secret load and just walked away . He's the only one in this shooting sports that wouldn't share information . Thanks for responding TJ12