Case neck turning questions

bpost

The package from K&M got here in two days. I got the whole shebang. Dial indicator for neck thickness, 6MM mandrel with doughnut cutter (carbide), and a 30 cal mandrel for my 30BR (when I get one!) and my 30-06. It also came with the expandiron for expanding the neck on virgin brass to the proper dimension before turning the neck thickness.

I have been practicing on some Remington 6BR cases to get the feel for things. The Remington brass has a very noticable variance in the neck wall thickness. The Lapua does not, it is almost perfect.

Some questions,

will new brass have to be turned again after a few firings?

is there a critical thickness for the neck wall that should not be reduced? It is running .0011 thick now.

nononsense

bpost1958,

Congratulation on the new tools!

will new brass have to be turned again after a few firings?

No, it's a one time operation. You may have to trim the overall length but you shouldn't have to turn necks more than once.

is there a critical thickness for the neck wall that should not be reduced?

I was trying to think of a good smart-aleck remark but I thought better of it. The critical thickness depends on the diameter of the neck area in your chamber. The thickness of the neck, or rather the diameter including a seated bullet needs to be less than the diameter of that neck area in the chamber. That way when the cartridge is fired, the neck material can expand enough to release the bullet. Check with your gunsmith to see what specifications he used to cut the chamber and ask for his recommendations. My chambers are mostly very tight and I turn to a tighter set of specifications.

Neck tension has an effect on the efficiency of the load and on accuracy. It's a variable that gets used to test performance. More tension may get you better accuracy and a cleaner burn from the powder but with an increase in pressure. Less tension is a balance achieved with care because the pressure goes down and you may get dirty necks and inconsistancy. Check your dies and measure what tension they put on your cases. If you have bushing dies, you just change out the bushing to adjust neck tension.

The thinner the necks are turned the less tension they can apply to the bullet. The thinner necks (I mean real thin) will simply come off from the case under higher pressure.

I have a 22PPC that is 0.0095" per side. One of my 6BR's is 0.011" per side like yours. My 6.5 WSSM is 0.015" per side and that included quite a bit of turning considering that it started at 0.019" per side.

Best.

FrancF

quote:Originally posted by bpost1958


I have been practicing on some Remington 6BR cases to get the feel for things. The Remington brass has a very noticable variance in the neck wall thickness. The Lapua does not, it is almost perfect.


[:D][:D][:D]
forgot to add- as you know, and for the other folks,
keep that bass to a dedicated gun.

JustC

boy you done it now, that K&M tool is gonna have you dropping brass shavings all over the house and looking for new loads of brass to work on[:D]

Great tool. Nononsense has it covered on turning. The bushing dies allow you to change neck tension no matter the neck thickness, but if your neck is a bit large and the brass a bit thin, you will work harden it faster. Get a dimension on your necks from the smith (or a fired case +.001" springback) and then determine how much your necks will expand during firing from the sized position. If it is a large amount, then find thicker brass and turn that down so as to have thicker necks AFTER they are turned. Adjust the bushing size and have at it.

good luck, post some range results.[8D]

mrbruce

I have on occasion turned down necks just enought to let the bullet out and no more.
Even some old stool shooters sized the cases just enough to let the bullet out, and some even to the point of not even sizing them at all, just pop out the primer, pop in a new one, and add powder, and a long seated bullet, and let the throat push the bullet into the case, and fiire away !!!

When I do it that way SOMETIME the necks will get tight again and I have to recut the necks to get back to the original size. I like them to make a POP sound when a bullet is pulled out of a fired case. Thats cutting kinda close, but I like close.

The K&M cutter will cut to 1/10th of a .1000

Nodays I want more neck tension so I quit doing that, but stll now and then I need to cut the necks thickness back again. The brass must flow into the necks to make them do that I would
think, don't you ?

JustC

that usually takes place faster on the cases with greater tapers,..right? it is flow from the body I beleive and is something we just have to watch for.