Neck Tension

[Ovenpaa]

I often think about neck tension, you know that variation in pressure required to push a bullet into a finished case and how sometimes it seems to need more effort than other times?

Anyway I have been looking at this, the K&M Arbor press with a Bullet-Seating Force Gauge,

http://bulletin.accurateshooter.com/200 ... n-vs-time/

Has anyone tried such a thing or experimented with methods to maintain consistent neck tension?

[FredB]

From a straight mechanical engineering point of view, considering the forces and acceleration acting on the bullet (around 29000g!), neck tension is just not relevant. More important is bullet jump--hence top USA lead bullet shooters breech seat the bullet into the barrel. I shoot a lot of 8.15 x 46R with a "stop-ring" bullet. De-cap, re-cap, add powder and seat the bullet by hand. The Lee liquid alox holds it in well enough for handling. Accuracy up to 200yds,(all I shoot) is superb.
Fred

[Dangermouse]

Crikey, FredB I take it that you do not load from a magazine, guessing that you must be a bench rest shooter?

As Ovenpaa knows, this was a real concern for me as we finished this season - my first season hand loading. Despite what I thought was consistent practises from case to case I was getting what I felt to be an unacceptable range of resistance when inserting the heads, from not even finger tight to being able to feel some resistance through the press.

I was planning on purchasing the Redding Bushing competitive neck die set http://www.sinclairintl.com/.aspx/pid=3 ... t__308_Win as this appears to address this issue, and others, that I have with my Lee dies.

DM

[Ovenpaa]

Fred, I do think this is a feel good thing, and for me, knowing everything is consistent is one thing less to think about at the range.

For my 7mm I jam by .005" and keep neck tension to the minimum I can without getting bullets stuck and a chamber full of powder if I have to unload and show clear. Bullet run out and neck tension both seem to have an impact on accuracy at longer distances especially the run out even when jammed. I aim to keep run out to a minimum and keep the worst ones for fouling and shorter distances. I have not tried any of the straightening systems and my view is pulling and reseating the bullet just makes things worse. In an ideal world I will keep run out to under a couple of thou.

[Sim G]

John Lee looked at neck tension a lot, didn't he? Months of experimentation....... the result, the Lee factory crimp die.

[Ovenpaa]

I have a cheap Lee press with an equally cheap bog standard Lee die permanently set up for putting 147 grain .308's together for plinking. Consistency and run out is stunningly good.

[woody_rod]

From a straight mechanical engineering point of view, considering the forces and acceleration acting on the bullet (around 29000g!), neck tension is just not relevant

Lots of evidence does not support this statement. Even at our own reloading bench, we now have seen the massive difference made by even neck tensions. Here is what happened:

My wife uses a 223 Rem in F standard. After having spent many hours and loads doing testing, we got to a point where the rifle would reliably shoot 0.5MOA groups. This was good initially, but after a few hundred rounds, the accuracy just started to go off a bit. We persevered a while with it, but it was obviously not good enough.

After obtaining a few internal neck reamers for our calibers, we started to ream all our case necks. We use only good dies such as Redding and Forster, with low runout on loaded rounds. I had noticed quite wide ranging neck tensions while loading the 223 in particular, which was eventually identified as issues with "donuts" (build up of brass at the base of the neck from it flowing forward from the shoulder). Now that these were gone, and having no other changes to the loads, they went from mid 50's to 60's immediately (60 possibles in AU).

I am a person that bases my ideas on facts, and this certainly showed me that even though it is hard to quantify from an engineering point of view (something I know a fair bit about), it definately does make a difference. Ask any BR shooter about this. F Class shooters (et al) may say they are not shooting BR, but the concepts can be used for free, using their many years of hard work as a basis.

I now ream all our necks, and am careful to make sure neck tensions are even.

[rox]

http://bulletin.accurateshooter.com/200 ... n-vs-time/

Has anyone tried such a thing or experimented with methods to maintain consistent neck tension?

I use Redding bushing dies with circa 1 thou of neck tension (OD reduction vs loaded round, not accounting for springback), but factors other than neck tension can have a significant effect on seating force, such as the condition of the bearing surface, hardness of the brass etc. When the seating force varies I expect to see more variation in seating depth. To keep the seating force constant I run the necks up a phosphor bronze brush spinning at low rpm in a drill press (*before* sizing the neck), then charge and seat the round without too much time delay (preferably same day, and ideally within a few hours). If I feel a variation in seating force on my (non-compound) press it usually manifests as increased variation in measured seating depth, and can usually be explained by some slight difference in case prep or case history (such as when I cleaned the necks on a PB brush *after* neck sizing). I reckon if my press had a seating force gauge the super-@nal in me would reject 2 out of every 3 rounds I loaded! Having said that, there are claims (admittedly from seating-force-gauge sellers) that sorting and grouping ammo by seating force produces more consistent velocity. However, my understanding has always been that (if the chamber permits) the case mouth opens and completely releases the bullet before the bullet starts moving; if this were the case how could tension/grip have an effect on ballistics or accuracy?

Incidentally, I make cosseted target rounds, uncrimped, in .308 for single-loading, and they would probably not be suitable for the forces experienced in a magazine, loading via feed ramp etc. Maybe the greater neck tension necessary for magazine use inevitably results in greater variation in seating force?

Bob.

[Ovenpaa]

That is a truly a work of art as much as a firearm, I am going to ask admin to split this thread and move your last couple of posts to the Military and Historic section as I have a whole load of questions I would like to ask specifically about owning/reloading/shooting such rifles.

Hope this is OK?

Admin is this possible?

[Christel]

Sorted