Neck Tension Question

[.300winmag]

As most of you know, I acquired a 6mm BR within the last month. However, I have now gone through my 100 pieces of Lapua brass I bought new. I have a bushing neck sizing die and have bought 3 bushings to go with it. I have a no turn 0.271 neck in my chamber, and with new Lapua Brass, I have loaded case necks that measure 0.270". Which is snug but performing well. I initially started with the 0.267 sizing die and groups opened up at 100 yards. I could also feel a great deal of difference between new cases versus the resized cases. The new cases had a great deal more resistance while seating bullets. Thus, I switched to a tighter neck, I went to the 0.266 bushing. Tension felt about the same with this die as it did with new cases; so I thought it was good to go. I shot several groups at 100 yards in the neighborhood of 0.140 inches, which is what I had gotten with new brass. However, I stretched it out to 513 yards the other day and shot several groups. All groups were within or below 1/2 MOA,, it was calm and ideal conditions and my problem was vertical stringing. I sorted bullets by ogive and weight, and all cases were sorted; then all powder charges were weighed. Finally OAL of cartridges were sorted (all were within 0.001"). I had on the worst group 3" of vertical spread! Windage was within an inch. I am meticulous when it comes to hand loading; I weigh cases, weigh bullets, then measure bullets am and a little confused with these results. I think the issue from my engineering background is the internal stress of the case necks being inconsistent and resulting in inconsistent neck tension of the bullet in the case, or different neck release temperatures based upon the metallurgical composition of the cases, as two will never be the same.

I've never annealed cases, as I've never experienced any real difference with the calibers I shoot. However, with this rifle and loads, I'm seeing the difference, and am wondering if my assumption with neck tension are correct in the vertical stringing and will annealing my cases help mitigate this issue? Maybe I'm asking too much of this cartridge, but I have read article after article of 6mm BR's shooting sub 2" groups at 600 and am bound and determined to get mine to shoot that well.

Thanks in advance!

 

[Ridgerunner665]

Whats the velocity like on the loads?

That would be the first thing I looked at...how consistent are they?

Whats the ES and SD look like?

This might seem redundant...but its the quickest way to tell if its an ammo issue or a barrel heating issue, possibly caused by stock bedding.

If the numbers are good on the ammo...its something else.

Sent from my DROID RAZR HD using Tapatalk

 

[Ridgerunner665]

Also...If I understand your post right...you're using new brass...that shouldn't need to be annealed.

Edit: Reread it...I see you are past the new brass stage.

Sent from my DROID RAZR HD using Tapatalk

 

[Ridgerunner665]

Another possibility...

You said your OAL was within .001".

Is that measurement from the bullet tip or the ogive?

If its from the tip...that is probably your problem.

Sent from my DROID RAZR HD using Tapatalk

 

[Vince]

While there are many factors, vertical stringing has usually indicated a bedding issue from what little I know.

 

[Ridgerunner665]

I think his groups at 100 yards are a key here...the groups grow more than they should at distance.

It could be neck tension...but that's not the first thing I'd blame on once fired brass.

A bedding issue would probably show itself at 100 yards too...but knowing the velocity spread of the load might provide insight as to the cause.

Sent from my DROID RAZR HD using Tapatalk

 

[hubcap]

Nosler manual no.1 does talk about vertical stringing. Basically it says on page 141 changing to powder with a different burn rate can control group shape. It also addresses stock bedding, wind and barrel heat mirage. I know I have had success resolving vertical stringing in the past by changing to a different powder.

 

[longrangehunter]

I just got over having these same issues as well, only for me it centered around the loaded neck rounds being too tight in the chamber. I tried using that tight of a neck clearance and it didn't work for my gun, a Hart Rifle Barreled (7mm-08 Rem.) using necked down Lapua 308 Win. brass. The loaded rounds only left .001" of clearance,they measured (.3150"-.3155") so I neck turned them down to .3130" which leaves .003" clearance for neck expansion. My groups went back to the norm.

My experience with the 6.5/300 WSM was the same..... so I avoided having a tight neck altogether. Besides, necking turning sucks!

 

[longrangehunter]

Try this: See if a bullet will go into the fired case? If it's tight enough to hold a bullet in place then maybe that's your problem? Also, new brass has a lot more resistance then fired cases while seating bullets. The burnt powder acts as a lubricant helping bullet seating, so don't go by feel off the ram alone.

 

[rick smith]

Think Redding recommends 0.001-0.002 less than loaded neck diameter. Might try less neck tension rather than mopre. Rick.

 

[257 Ackley]

Do you have a concentricity guage? If you do, check a case after you resize and see how much runout you have in the neck. How is your bushing die set up for a shoulder bump? You should not have to worry about turning necks if the chamber is .271 unless the bore is not aligned properly. Some guys turn their necks even with a .272 neck just to have even neck tension all the way around. What primer are you using? A change in primers will help sometimes.

Try a ladder test at 300 yards with several different seating depths making sure everything else is the same. Some bullets don't tell you how accurate they will be until they get to the 3-400 yard mark. Once you find the seating depth the barrel likes, you can do ladder tests with powder charges a few tenths of a grain on either side of what has worked (around 30 grains of Varget) to see if you find the sweet spot.

If I remember correctly, you have a fairly heavy contour on the barrel so heatup shouldn't be a problem with such few shots. We shoot 22 rounds within 20 minutes for score in a match (usually done within 10 minutes unless the wind and mirage are changing quickly), with most guys shooting palma and HV contour barrels with vertical stringing under an inch at 600 yards.

 

[woods]

Like ridgerunner said, to control vertical spread at distance you need to control velocity Extreme Spread and Standard Deviation. IME a large factor in controlling that is finding the right seating depth. Note this seating depth test

.015" off - ES 31, SD 11.67
.030" off - ES 31, SD 11.70
.045" off - ES 23, SD 9.80
.060" off - ES 8, SD 4
.075" off - ES 27, SD 11.40
.090" off - ES 52, SD 31.70

You haven't mentioned your seating depth or your velocities yet

 

[Oldtrader3]

The thing that strikes me with neck tension is the amount of force increase due to small I.D. changes in the neck. The force required to add an additional .001 inches is compounded with neck postforming, hooptension and springback which may result in higher neck tension (depending on hardness) for the first couple reloading cycles after reforming. I would, if you are not already, anneal the necks before forming and let the finished ammo sit on your shelf for a day or two of hoop tension relaxation before testing at the range and shooting groups?

 

[HOGWILD338-378]

Give Redding Tech a ring ? (607)753-3331 :mrgreen:

 

[.300winmag]

Well I took all of your advice and called redding as well. Their recommendation was to remove the button from the die. I did so and it made a huge difference. Thanks to everyone that chimed in on this post.

 

[HOGWILD338-378]

Glad ya got the problem addressed and hope it fixed your issue!!