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Neck Turning - Minimum Wall Thickness
- Thread starter BearNaked
- Start date
If I understand your question you may be looking at neck-turning all wrong.
I am sure you will need to do some turning to get inside normal specs with the converted LC brass but just how much?
What is the true neck diameter of your 260 chamber?
That alone will determine your ideal neck wall thickness. You want your loaded rounds to be .002 to .003 under the chamber's neck diameter.
I am sure you will need to do some turning to get inside normal specs with the converted LC brass but just how much?
What is the true neck diameter of your 260 chamber?
That alone will determine your ideal neck wall thickness. You want your loaded rounds to be .002 to .003 under the chamber's neck diameter.
No, I am not saying you have it wrong. You do need to neck turn but just how much is the question. Nothing good comes from having them too thin.
Let's say your SAAMI reamer neck is .294" or so. Measure a loaded round and it should measure .002 to .003 smaller than that for proper clearance.
Another way we can look at it it, if you have any loaded 260 ammo, measure a loaded round for reference. Do you have the tools to neck-turn? Or a tube mic to check the thickness of your converted LC brass neck wall?
EDIT:
as reference, I measured brass from my 260. The neck diameter of a fired piece is .295 and loaded rounds in Lapua brass are .2915. You should be operating in that range. If you can measure with a tube mic give me a neck thickness on your converted brass.
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Bearnaked,
take 10 pieces and tube mic then like shoot4fun said.
Most likely case is since youre neck turning, might as well
even them all out. Find the thickest , thinnest and get an average.
Make sure you hit them with the expander mandrel first before measuring
take 10 pieces and tube mic then like shoot4fun said.
Most likely case is since youre neck turning, might as well
even them all out. Find the thickest , thinnest and get an average.
Make sure you hit them with the expander mandrel first before measuring
I've always measured several with a ball mic and figured what my neck thickness should be from there.
With this number you should look for a 80-90% clean up on the necks.
Rarely has this been below .013.
As mentioned above run them through an expander to move all the imperfections to the outside.
I use a little imperial wax to lubricate the cases when i turn them.
R
With this number you should look for a 80-90% clean up on the necks.
Rarely has this been below .013.
As mentioned above run them through an expander to move all the imperfections to the outside.
I use a little imperial wax to lubricate the cases when i turn them.
R
I didnt mean to come off rude. I just read what i wrote again. I have been reloading for a while but never needed to neck turn so this is something very new for me and that is why i have asked the masses for yalls knowledge.
I have always seen people turn their necks to about .015 neck wall thickness and i think mine are already at that. (yes every rifle, chamber, reamer, etc are different but i was using this as a reference only and not my actual measurements.)
The reamer cuts to .298 and the neck fits completely in but just a small ring is too high. so if i cut it down i just wanted to make sure that i am not cutting it too thin. so if my neck of the chamber is .298 - .264 bullet = .0336/2 = .0168 so call it .016 - .002 =.014 should be what i cut my neck to?
I will do all the measurements tonight but i think i was around .013-.015 when i checked it after resizing it. My brand new K&M tools will be in on friday so i will be very busy then.
just curious though, what is too thin? .010? .012? .008?
i will have to wait to get my measurements then until my neck turn comes in on friday. thanks for the heads up and the info.
I didn't take it as being rude.
Neck thickness is not the same across brands of brass; not even within a certain brand always. There is no "standard" for neck thickness per se but it should all be made to work with SAAMI spec chambers.
.298 is big for a 260 reamer. .264+.015=.015= .294 so you should be clearing the chamber by .004 which is plenty of expansion.
It sounds to me like you may have another issue if only one are of your neck isn't clearing.
ok good. i usually have an issue typing direct and it coming out like an ass so i always have to check how i type stuff out.
i think what has happened is a donut has formed on the inside on the neck case or the outside of it which is causing this. i did order the cutting pilot so this should take care of any donut inside or out.
And just to make sure, thats what reamer you used? Or is it just a generic print from the web? PTG makes all sorts of different reamers and it can depend on what each individual smith specs.
.298-.264=.034 of total area in the neck not taken up by the bullet .034/2=.017 of space on each side .017-.002=.015 brass thickness with .002 clearance so you should be aiming for the thickness to be .015
If its a bit thinner than .015 thats alright but just know that it means your brass will be getting worked more than necessary on each firing.
If you dont know if .298 is the actual dimension of the reamer used by your smith then you need to ask him.
Some people could run .008 for bench rigs or something with super tight tolerances but their chambers are cut tight enough to necessitate that. Something on the order of a .282 chamber neck diameter would facilitate the .008 thick necks. You wouldnt want a neck that thin in a saami spec chamber. They would split in a heart beat.I personally wouldnt want a chamber that tight either. To remove that much material you would want to turn them in two passes, one taking them half way down and the second all the way. The minimum thickness .004 less than your chambers neck.
Theres no set line in the sand for how thin or thick you can go, it depends entirely on your particular chamber. If youre going to turn you need to know your exact dimensions if you want to be going about this properly.
Also note, calipers arent good enough for this and you will want to get a micrometer to accurately measure the necks. Calipers will float along the high spots ignoring the low spots so youll never really get an accurate or repeatable measurement.
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Also, the first question that should have been asked: what die did you use to neck down from 308 to 260? It should have been a normal full length die and not a bushing die as the bushings have a radius on them and dont size the neck the entire way down. That could be the bump you are feeling, just unsized neck and not too thick of a neck. If thats what happened and you trim that unsized neck down you will be effectively removing a bunch of the meat that is vital for holding it all together. e.g. you upper neck will measure .014 post trim and your lower neck would measure only .010 thick. And just like bending a paperclip a bunch they could separate from over working.
Have pics of the scratches?
Have pics of the scratches?
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This measurement came from a reamer print from Northland Shooters Supply but i think this was chambered by shillen and that is the reamer they use to cut it.
my next question is, if i need to hit .015" and i have some low spots then is it ok for it only to cleans up 20-30% of the neck?
thanks for the answer. my mind just doesnt accept what is. i always want to know the limits and why.
Hornady 260 Remington Custom Grade Reloading Dies(Series III Two-Die Set)
i didnt have to trim the cases since they were about .010" shorter than saami. 2.025" case length and Saami says 2.035"
i dont right now and i did some more testing to the case last night so they might be gone but i will see if the marks are still there and ill send a pic if they are.
Yes. that is what i got from NSS. that is where i was getting the neck diameter. i will find out more this weekend when i go shoot it.
Make sure you write down the pre and post firing measurements to see just how loose your chamber neck is for your brass. I suspect that since youre using full dies that it could just be spring back from going .308 to .264 in one step. Many recommend a 7-08 die as an intermediary step to alleviate that. They should be good after firing though if your neck really is .298.
http://forum.accurateshooter.com/threads/lc-308-brass-to-260-brass.3922601/
I have heard to do the 7-08 before but other people were doing it without it so figured i would cut some of the cost with all the money i spent getting my rifle to where it is. i ran the brass several times through die to make sure that it is set back properly.
