.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.

 

[JFrank]

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.

That went right over my head'
J

 

[JFrank]

There are certainly people that use ~.001 interference fit neck tension for F-TR loads with good results. I personally prefer to keep them a tick higher around .0015" to .0025" and probably wouldn't recommend going much lower than .001" for obvious reasons. I haven't experimented exhaustively with neck tension, usually just selecting the bushing that gets me close to .002", not all bushings being equal . But you can always tweak other parameters of a load over a range of different neck tension settings and still come up with something decent that will likely never be the limiting factor. So your .001" should be fine, get the load tuned with that and it will work. However, if you ever decide to change the neck tension, you will probably need to retune the load.

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

 

[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

 

[JFrank]

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

I run mine with the numbers up
However Wilson web site has a neck sizing video where dude says it can be flipped over, check it out and let me which is correct as I only have .0015 hold- that's not much . It's right in between my two Mandrel s .241 and .242 my bushing is .266 ???
Jim

 

[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

 

[JFrank]

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

If my 308 would shoot a 1/2 in at 200 I'd still be shooting it.
Nice job Chris!
J

 

[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.

 

[JFrank]

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.

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

 

[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.