So how important is neck tension?

[BoydAllen]

On the internet, the word jam seems to have come to mean many things, some of which are rather imprecise. The classic short range benchrest definition is the longest seating that will not result in the bullet being pushed back into the neck when the round is chambered....at the neck tension that will actually be loaded for shooting. When used that way, jam refers to a dimension. For example, a friend has found that for his powder and bullet that seating longer than jam by .006 or so, so that the bullet is pushed back to jam (length) as the round is chambered, gives him his best accuracy when shooting his bullets and LT 32. The way the term is used in this sport, if one were loading .006 shorter than jam, he would probably say that he was .006 off jam. Shooters have used jam because it is an easy to measure reference. Load a round long noting your die adjustment, and the OAL of the round. Chamber the round (or dummy), and then remeasure. If you want a specific amount off jam add that to the difference between your first and second measurements and extend your seating stem by that much. Because you are doing all of this with one bullet, Ogive length is not needed, but you can take and record that measurement after your bullet is seated to your preferred length. Personally I skip that and simply record the combined length of my Wilson seater' stem and cap.

 

[Tim Singleton]

Boyd, any idea whose die Gary is shooting?

 

[Brians356]

Personally I ... simply record the combined length of my Wilson seater' stem and cap.

I particularly like that idea.
-

 

[BoydAllen]

Tim,

The bullet dies are by George Ulrich, and the FL die is a Redding SB.

Funny bullet making story that Gary Sinclair told on himself: After buying several expensive carbide point dies to try to cure an intermittent accuracy glitch, Gary found out that the problem was his squirt die, which was turning out cores that were just a little too big in diameter, causing some trapped air issues. When he mentioned this to Gary (his gunsmith) Gary told him that he had been using .22 cores to make 6mm bullets since he started making them. Looking at this agg. I would say that they work just fine.

Boyd

 

[JamesnTN]

Assuming all things equal, would more neck tension raise pressure or FPS?

DJ

Here's a prime example of increasing neck tension and what it does on paper. These were shot at 500 yards from my 300 WSM. Everything was the same other than the noted neck bushing changes. You can see the velocity rises as the ES and the SD drops as I tighten up the neck bushings.

 

[BartsBullets]

South Pender,

You are turning your your necks way too much! I shoot a .268 chamber and turn my necks to 11.5.

For a 6ppc shooting out to 300 yards neck tension is WAY down on the list as far as accuracy. As long as your neck tension is CONSISTENT and your bullets are being held in place with the rifle you are shooting, you're good. This is very contrary to what guys shoot 600 yards and further will tell you. Also, all the talk about shrinking ES because of finding the correct neck tension does not apply! Not for short range and a 6ppc


Get some flags, learn good bench technique and your groups will get smaller. It's NOT going to get there trying to tweek neck tension.

The bullets you are shooting are capable of shooting groups consistently in the 1s. You just need to find out what your gun and for that matter what you can shoot. Enjoy figuring it out.

Bart

 

[South Pender]

South Pender,

You are turning your your necks way too much! I shoot a .268 chamber and turn my necks to 11.5.Bart

I hear you, Bart! The reason I turned the necks to 9.5 is that I'm using Norma 6 PPC-USA brass which seems to have very thin necks right out of the box--apparently much thinner than found on Lapua 220 Russian brass. In fact, I'd estimate the unturned neck thickness to be about 11 (I don't have the necessary tool to measure it precisely). Since I assumed that the neck thickness might not be perfectly uniform on the unfired brass, I turned the necks to make sure that neck thickness would be perfectly uniform all around the necks--removing any possible high spots. It's possible I overdid it a little, but not by much, I think. Perhaps with greater care, I could have stopped at 10, instead of 9.5, with uniform removal of brass all around the necks of all the brass in the bunch.

Get some flags, learn good bench technique and your groups will get smaller. It's NOT going to get there trying to tweek neck tension.

The bullets you are shooting are capable of shooting groups consistently in the 1s. You just need to find out what your gun and for that matter what you can shoot. Enjoy figuring it out.

I have just picked up some wind flags (although learning how to read them will take some time), and I'm working on my bench technique. I'm completely confident in the two bullets I have been loading, and with what I'm learning from my range sessions, I think groups will improve. I'm definitely not looking for another variable in the equation to tweak, and my purpose in starting this thread was just to determine whether neck tension was in any way relevant. I'm now thinking that it probably isn't--at least in my case, shooting a lightweight sporter. I'll have a better idea after my next range session when I'll be shooting rounds with .001" tighter neck tension than before.

 

[oldroper]

I hear you, Bart! The reason I turned the necks to 9.5 is that I'm using Norma 6 PPC-USA brass which seems to have very thin necks right out of the box--apparently much thinner than found on Lapua 220 Russian brass. In fact, I'd estimate the unturned neck thickness to be about 11 (I don't have the necessary tool to measure it precisely). Since I assumed that the neck thickness might not be perfectly uniform on the unfired brass, I turned the necks to make sure that neck thickness would be perfectly uniform all around the necks--removing any possible high spots. It's possible I overdid it a little, but not by much, I think. Perhaps with greater care, I could have stopped at 10, instead of 9.5, with uniform removal of brass all around the necks of all the brass in the bunch.


I have just picked up some wind flags (although learning how to read them will take some time), and I'm working on my bench technique. I'm completely confident in the two bullets I have been loading, and with what I'm learning from my range sessions, I think groups will improve. I'm definitely not looking for another variable in the equation to tweak, and my purpose in starting this thread was just to determine whether neck tension was in any way relevant. I'm now thinking that it probably isn't--at least in my case, shooting a lightweight sporter. I'll have a better idea after my next range session when I'll be shooting rounds with .001" tighter neck tension than before.

When Sako first came out with 6ppc, I purchased one and 22ppc. I still have 22 ppc and I don't turn neck on 22ppc or 6ppc when I had it. I shot Norma bass as is and I still have some 6ppc. The Norma brass I have runs .011 to .0115 and I could clean up the necks to .011 but as good as that 6ppc shot, don't think it make difference.

If you fireform Lapua you can turn those necks based on that chamber and have better case.

You need good ball mike for those cases so you know what your starting with.

This is from BR on Norma 6ppc brass.

http://benchrest.com/showthread.php?97671-Norma-6-PPC-brass

 

[hogpatrol]

re: Neck Tension.

After reading some of our more "notable" members posts on topics such as headspace, shoulder bumping and chamber measuring, the only issue I have with neck tension is I can't reach through the computer screen to utilize its positive effects.

 

[joshb]

Where's fluffy on this?

 

[22DASHER]

Where's fluffy on this?

Here you go:

@fguffey

 

[seymour fish]

With all due respect, I seriously doubt that gun will shoot into the 1's and 2's no matter what is tried. Sako's are nice, but the fact remains it's a factory sporter and will perform accordingly. If the OP starts chasing his tail in pursuit of 2's he'll end up in load development mode for the life of that barrel and in the end will never get there.

Had a 25-06 sako pillar bedded that shot on the ones, still have a 223 heavy bbl sako, pillar bedded that shoots in the ones. Factory bbls. 5 shots.

 

[seymour fish]

Had a 25-06 sako pillar bedded that shot on the ones, still have a 223 heavy bbl sako, pillar bedded that shoots in the ones. Factory bbls. 5 shots.

Load development was not problematic

 

[seymour fish]

I haven't read the entire post , but in my personal lifelong 6 PPC guest for accuracy , WHEN IM HARD JAMMED ! NECK TENSION MEANS LITTLE !

GgMac, exactly. It becomes lost in the noise floor !

 

[Toby Bradshaw]

Had a 25-06 sako pillar bedded that shot on the ones, still have a 223 heavy bbl sako, pillar bedded that shoots in the ones. Factory bbls. 5 shots.

In benchrest, shooting in the {zeros, ones, twos, etc.} doesn't mean that the rifle has done it once. It means that it will shoot for aggregates at that level. See Boyd's post #38 in this thread for the kind of evidence that's required.

 

[David Christian]

I agree with Richard. Your neck clearance is 3 times what it should be which makes sense that your rounds like to be jammed. Without the jam, your rounds are rattling around in the chamber quite a bit and when fired don’t hit the lands in a uniform way. Try a new case of brass without turning them.

 

[Bart B.]

Your neck clearance is 3 times what it should be which makes sense that your rounds like to be jammed. Without the jam, your rounds are rattling around in the chamber quite a bit and when fired don’t hit the lands in a uniform way.

Doesn't the firing pin (or in-line ejector) drive the case shoulder hard into and centering in the chamber shoulder well centering the case neck and bullet in the bore firmly before the round fires?

If not, why?

243 Win cases center their neck and bullet in 308 Win chambers perfectly when fired.

 

[mikecr]

Yes, I am neck-turning, and have turned the necks to about .0095" thickness. (This I infer from the fact that a round with a seated bullet mics about .262", and the bullet mics .243".)

The diameter of the neck of a fired case is about .269".

Your necks spring back ~1thou of chamber so you have a ~.270 neck chamber. Why would you turn necks for 7thou of clearance(.269-.262)?

Up until now, all my loads have used the .260" Wilson bushing, and so I have assumed that this means .002" neck tension.

Why would you think this? You turned necks, but didn't measure & know what your interference fit is?

I've just changed the Wilson bushing to the one marked .259" and have sized the cases with it. Measuring the sized portion of the neck (about the last .18" of the neck) gives .258", and so this is about .001" tighter than I thought I was getting with the Wilson .259" bushing.

Bushing sizing greater than 5thou causes more sizing than stamped, due to excess sizing angles. You're sizing necks too much because you're expanding necks too much on firing.