Necking down - how much does the neck thickness increase?

[Keith Glasscock]

I am working with a 308 that has a rather large neck. The fired cases come out at .343"

Loaded rounds in Win brass run .332" and Lapua runs .338" Even .005" is awful hard on brass - I'm thinking of trying something unique...

If I were to neck down a larger brass such as 338 Federal or 358 Winchester, how much can I expect to increase the neck thickness in the neck down process?

Anyone got a case or two (culls that aren't going to be shot anyway) that I can try this on?

Thanks!
Keith

 

[ohearchai]

Keith, after a lot reading I have came to the conclusion that. 343 isn't really that large, in fact it may be the norm for quite a few 308 shooters. I did take some pointers and I size down in 004 increments now, to .339 then to. 336. My Lapua brass is holding up very well, I have only lost a few cases out of a couple hundred that have at least a dozen reloads through them.

 

[Keith Glasscock]

I'm just thinking that running a loaded neck of .341" might be a good thing. It would save me from needing to anneal quite so often. Has anyone used Norma brass? Are the necks thicker, thinner, or the same as Lapua (.015")? I hate buying brass just to find out things like neck thickness.

 

[MrMajestic]

Re-barrel to a .340 neck, problem solved! ;D
Is your accuracy acceptable? If so, as they say in NY, forget about it!

 

[Keith Glasscock]

The accuracy meets my needs That is why I wont rebarrel at this point. I will, however, spec a different reamer for the next barrel/build. It will be a .335 neck. That way I can use whichever brass suits my fancy - I turn everything anyway.

I'm just looking for ideas that would reduce the amount of time I have to spend in the shop. Right now, I have to anneal frequently regardless of brass used.

If I use Winchester brass, I actually have to FL size every firing in order to obtain decent runout(s). In all, I spend about 5 minutes per case, per firing.

 

[jonbearman]

Just out of curiosity,what dies are you using and which press.Also do you use bushing dies without the expander or with the expander.I have found many expanders in several manufacturers dies to pull the neck out of square unless you lube the heck out of the neck befroe sizing.I now have gotten away from expanders in a few calibers using redding bushing dies. You probably know this but I like to be sure if that is the problem.

 

[MrMajestic]

Busdriver,
I take it from your reply you don't have automated annealing equipment. I anneal every load cycle as it only takes several minutes with my Bench Source. If you want thicker necks I would think sizing down '06 cases would give you what you are looking for. ohearchai's methodology is sound for your expected results also. jonbearman's statement is correct also. I don't turn necks except those with tight necks as I abhor it! I also don't use an sizing die based expander opting for bushing dies and a separate expander die and dry graphite lubed necks. I check runout on all my loads with a Neco base and .00005" graduation indicator and wish I could say all my loads were +or- .001 but that is not the case. I don't think that is obtainable with my equipment but perhaps with arbor press type. Wish I could be more help but with acceptable accuracy I stand beside my previous statement, "Forget about it" and enjoy your time in the shop away from all your worries!

 

[Clark]

I know there is conservation of momentum and conservation of energy.

There must be a conservation of neck mass.


With standard 257RAI, 243, and 260 reamers:

a) I have necked 8mm -> 7mm -> 257 Roberts AI without interference.

b) But 308 -> .243 makes real trouble.

c) 308 -> 260 makes trouble ~ 10% of the cases.

What does it all mean?
No trouble
Lots of trouble
Trouble sometimes

 

[Keith Glasscock]

Just out of curiosity,what dies are you using and which press.Also do you use bushing dies without the expander or with the expander.I have found many expanders in several manufacturers dies to pull the neck out of square unless you lube the heck out of the neck befroe sizing.I now have gotten away from expanders in a few calibers using redding bushing dies. You probably know this but I like to be sure if that is the problem.

With Win brass, I use a Hornady FL size die. I don't need an expander with it at all, and I get .002" of neck tension. I still do everything on my RCBS Rockchucker press and I rarely see even .002" of runout on sized necks. Most of the time, about .0005-.001

I'm not having any problem other than chamber fit. The 308 win chamber is just a bit too big for any of the brass I know about. I'd really like to be able to test a .002" neck clearance and see if I can get a little more out of my rifle.

 

[Keith Glasscock]

If you want thicker necks I would think sizing down '06 cases would give you what you are looking for.

I thought that was one of the silliest ideas I had heard of yet, but seeing as how I am feeling experimental, I tried it. I have a once fired '06 Winchester case that has a small ejector mark in the head, so away I went.

First pass (bump) in the 308 die moved the shoulder back to an approximate 20* angle.

Neck cut to half its original length and bump again, cut and bump, cut and bump

Here is the result - After neck turning for 100% cleanup, I have a loaded neck diameter of .3385 - I probably could have left it at .339

The case capacity is a bit lower than a once fired Winchester case 54.7 vs 56.2 grains of water

While this wont do quite what I wanted, it sure is interesting that I can make 308's out of '06 cases.

Anyone have an opinion on whether this would be safe to shoot?