Neck wall thickness for soft seating

[Donkey]

Hello everyone.


For those of you using light neck tensions and turning your necks what neck wall thickness's have given you the most consistent neck tension?

I'm using .308 Lapua brass.



Many Thanks
Jason Williams

 

[LongRanger]

Jason.....What you casually tossed out is a huge question. Since no one has chimed in to ask you to define what you mean by "light" neck tension (you can achieve light tension with thin OR thick necks)....

Whether .308 brass or any other, cartridge brass is frustratingly thin, plastic and variable at our shooting pressures.....lot to lot, case to case and firing to firing. If we can assume that a 1/2" thick neck would be pretty darn stable, we might then assume that thicker is better and that turning inside and/or out just enough to clean up thickness variability around the neck is the best bet for consistency for any amount of seating tension....at least for that firing, on that case, from that lot.

BTW... are you measuring "tension" with a force gauge, such as the K&M bullet seating force gauge? Or just going by the numerical difference between your sized and unsized necks?


Frank B

 

[Donkey]

Hey Frank.

Thanks for your reply. It is much appreciated.

I assume that those trying to get consistent neck tension (bullet seating pressure) at the light end of the spectrum have done some experimenting with neck wall thickness to determine which gives the least sensitivity to the variables you mentioned.

I have heard it said that thin neck walls are easier to use for soft seating. How ever I would assume, as you do, that a thick wall would be more stable. On the other hand a thin neck may be less sensitive to interference variations from sizing, turning, bullet variations etc. I guess it depends on which of the variables that you mentioned matter the most for light tensions.

I'm very interested to hear what peoples results have been trying to get consistent neck tensions with thick (.014") or thin (say less than .012")

If in fact it is true that thin necks are less sensitive to the relevant variables here then I would be interested to here if there are any down sides to thin necks.

The reason I ask is that I am designing my reamer at the moment and debating with my self on what neck diameter to set.



Any thoughts and comments are valued and appreciated.


Kind Regards
Jason Williams

 

[jo191145]

Jason

Seeing as your specing your own reamer I think thickness of brass will matter very little.
Thickness of brass begins to have effects when brass becomes hard and failure to obturate begins.
One of the reasons the very thick WSSM's have trouble I believe JMHO.
As long as the brass is kept in a soft state it should'nt make much difference unless your looking to shoot very mild loads. JMHO

Personally I'd go with lightly turned Lapua brass and spec the reamer .002" larger than a loaded rd.
Use of a bushing die will be mandatory for less working of the brass or a custom honed die.
I see absolutly nothing wrong with going with a thin neck either. Either will work, its up to you to keep the brass at a constant hardness.
FWIW the throat will have a great effect on perceived tension also. The deeper you stuff a bullet in the case the higher the tension becomes.

My best tip.
For soft seating I've found Imperial Dry neck lube greatly helps consistency. Brush it in the neck before charging and even a normal tension round will seat like butter. Drop down to .001" tension and you'll not even feel them seating. Sweet For a few bucks its worth trying and comparing.
Seeing as its dry the powder will not stick to it.

 

[limbic]

I take neck wall thickness into consideration. None of my chambers are that tight. I use bushings that are .001 or .002 smaller than a loaded round. I found my 260 Lapua brass was .002-.003 larger in diameter than the ff .243 I had been using. I simply bought some new bushings. Where I had been using .290 and a loaded round was .291 I bumped up to .293 with a loaded round measuring .294. Chamber is .297 fwiw

Also remember to anneal your brass when the seating gets tougher

 

[Donkey]

Thanks guys

Jo that is an interesting trick with the lube. I guess that would also stop them locking on bullet over time so you could load them early.

I'm thinking of going .0005" smaller than the reamer on the neck of the brass and relying on spring back to reset the neck size. That way I wouldn't have to neck size at all. Has anyone managed to achieve this?


Cheers
Jason

 

[jo191145]

Thanks guys


I'm thinking of going .0005" smaller than the reamer on the neck of the brass and relying on spring back to reset the neck size. That way I wouldn't have to neck size at all. Has anyone managed to achieve this?


Cheers
Jason

Jason

Oh Yeah thats been done. I'd call that "Old School" Benchrest techniques. Its how it was done in the old days by the pioneers of small groups.
To be successful the attention to detail is significant and IMO you had better be a Master Machinist with the tools to boot ;D Most of the pioneers were just that.
For the average shooter using average tools I'd not suggest going that tight. Over the years BR shooters have found those tight tolerances are not needed and usually counterproductive.
.002" is the norm in 6mm and 30 cal these days.
Some distinguished 30 BR shooters have gone to .003" with improved results.

When your dealing with .0005" any variation in brass/bullet thickness will create bullet release drag issues that will be seen on the target. Big time.
If your really up for the challege you could start there. If results are unsatisfactory its as easy as turning a little more brass off the neck to achieve a clean release. If your alive
Mess up your numbers just a bit and pressures ramp up very quickly to dangerous levels. Most likely with no warning. One of the hazards of dealing with a super tight neck.
I doubt you'll find anyone who recommends it these days but it has been done.

 

[Donkey]

Thanks Jo.

I thought as much. Everything has already been done before. Tell me is bullet release drag really an issue if you are soft seating?


I'm still interested in whether or not to go for a thin .012" neck wall with soft seating?


Many thanks
Jason