Effects of changing neck tension

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Jase PTRC
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Joined: Sat Nov 29, 2014 11:15 pm
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Re: Effects of changing neck tension

#16 Postby Jase PTRC » Wed Mar 01, 2017 9:16 am

Matt P wrote:Hi Jase
A few things, firstly looking at the picture of your turned brass, it looks like you haven't turned down far enough into the shoulder. This will cause doughnuts and depending on the throat length can cause accuracy issues.

Hi Matt, this was the initial turn on these cases they were turned again. the photos are a little deceiving. the cutter was going in all the way to the shoulder but because it was a very light first skim some cut and some didnt right down into the junction. on second turning the case necks were clean all the way down. I have a .040 free bore chamber and projectiles are a fair way out from the donut area.

What are using to measure your "touch length", reason I ask is generally depending on the tooling used the best you'll be able to measure is within 0.005". I recommend my customers to be at least either 0.010" in or out from that measurement, reason being they'll be either jumping or jamming and not in what I call "no mans land".

Im using a Hornady OAL gauge with a fired case from this chamber which i had threaded. I check 20 projectiles from a batch the average out the measurement from that. Im using a comparator on the ogive. Im running .010 jump. I have tried .020 and .015 but .010 works best so far.

In actual testing I have done, neck tension consistency is far more important than a particular number, lets face it a projectile with 60,000 PSI up it's arse, can it really tell the difference between 0.002 and 0.004 ???
Too much neck tension can distort the jacket, in my personal rifles I use a bush 0.002" less than my loaded round and anneal cases every reload.

Im annealing every third firing which all my cases are now at as i have to "borrow" some else's annealer. Would you recommend going a tighter bush on the third firing? If you do how much tighter?

If you don't anneal you'll probably need a smaller bush as the case ages and becomes more and more work hardened. I seat bullets using Wilson dies and an arbor press this give a lot more feel and allows me to set aside that odd round that seats easy or hard, I use these as sighters (and usually end up "in the group" anyway).
With regards to primers, every barrel is different and fine tuning of ES can be done with primers, I have 3 6mmBRAI barrels here and 2 of them get best results with CCI450's and the other with BR4's, same brand of barrel and same reamer.
Regards
Matt P

Jase PTRC
Posts: 221
Joined: Sat Nov 29, 2014 11:15 pm
Location: Adelaide SA "PTRC"

Re: Effects of changing neck tension

#17 Postby Jase PTRC » Mon Mar 06, 2017 9:24 am

Well it seems my fears may have been unfounded that my rifle was not performing. At 500mtrs this week my first round score was 59.6 with the dropped shot being perfect X ring vert and all the 6's were the same elevation. My personal best single round score at Lower Light so far so very happy. Im still going to try the BR4 primers at a later date just to see what happens, thanks everyone for your input. cheers.

memilanuk
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Joined: Mon Apr 22, 2013 1:09 am
Location: WA State

Re: Effects of changing neck tension

#18 Postby memilanuk » Sat Mar 11, 2017 3:15 am

Try jumping those 155.5s a bit more... like 0.050" off the lands. You might be (pleasantly) surprised...

RAVEN
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Re: Effects of changing neck tension

#19 Postby RAVEN » Tue Mar 14, 2017 12:12 am

Jase
I see one flaw in your process
When ladder testing always do it jammed I'm surprised pll in the know at your club haven’t told you that!
once the node and your max load has been established then experiment with loads either side of the node and try a few different jumps
shorter range is better for these experiments.

it’s important to do the ladder over a chrony and not one that attaches to your barrel
or at least run the node load over a mag speed the following week and record the velocity.
this is the velocity it will like to shoot at.
once you have found that sweet spot
try changing primers and see if it improves the SD at min 10 round the more fired the more accurate the info
Necks are a continuously changing thing
annealing will affect NkT
Brushing will affect NkT
dry lubing will affect NkT
the more firings on the brass will affect NkT
In fact, necks, will become thicker over time as the brass flows forward even though we don't have to trim length as much as with a standard chambering the brass will still flow to the neck
So, using a nk Bush die with expander ball to pull the neck down smaller than required then with expander ball expand the neck (usually give you about 3th NkT) this would probably give you the most consistent result.

RB

Quick
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Re: Effects of changing neck tension

#20 Postby Quick » Thu Mar 16, 2017 6:49 pm

Can you post some plots so we can see how your group looks at long range?

Your load could be fine and could be your wind reading instead? Hate to be devils advocate but Id also consider that.

Id take your load to 800m or further and see how it does going from 10 jump and keep going back until it opens right up. Or try a 10 Jam?
Shaun aka 'Quick'
Yanchep, Western Australia

308 Win F/TR & F-S
7mm F-Open Shooter.

Jase PTRC
Posts: 221
Joined: Sat Nov 29, 2014 11:15 pm
Location: Adelaide SA "PTRC"

Re: Effects of changing neck tension

#21 Postby Jase PTRC » Fri Mar 17, 2017 7:06 am

RAVEN wrote:Jase
I see one flaw in your process
When ladder testing always do it jammed I'm surprised pll in the know at your club haven’t told you that!
once the node and your max load has been established then experiment with loads either side of the node and try a few different jumps
shorter range is better for these experiments.

it’s important to do the ladder over a chrony and not one that attaches to your barrel
or at least run the node load over a mag speed the following week and record the velocity.
this is the velocity it will like to shoot at.
once you have found that sweet spot
try changing primers and see if it improves the SD at min 10 round the more fired the more accurate the info
Necks are a continuously changing thing
annealing will affect NkT
Brushing will affect NkT
dry lubing will affect NkT
the more firings on the brass will affect NkT
In fact, necks, will become thicker over time as the brass flows forward even though we don't have to trim length as much as with a standard chambering the brass will still flow to the neck
So, using a nk Bush die with expander ball to pull the neck down smaller than required then with expander ball expand the neck (usually give you about 3th NkT) this would probably give you the most consistent result.

RB


Hi Richard, My Ladder was done over a chrony and the load of 46.1 was right in the middle of an area of MV where it flattened right off at around 2975fps for a few shots before climbing again. I have not given using a neck expander any thought previously but i see where you are coming from as it will make the inside neck more concentric. Im yet to run the load back over a chrony to check SD.

Jase PTRC
Posts: 221
Joined: Sat Nov 29, 2014 11:15 pm
Location: Adelaide SA "PTRC"

Re: Effects of changing neck tension

#22 Postby Jase PTRC » Fri Mar 17, 2017 7:12 am

Quick wrote:Can you post some plots so we can see how your group looks at long range?

Your load could be fine and could be your wind reading instead? Hate to be devils advocate but Id also consider that.

Id take your load to 800m or further and see how it does going from 10 jump and keep going back until it opens right up. Or try a 10 Jam?


Hi Shaun, I am working on getting some plots put together over the next few weeks hopefully once i get some teams events out of the way.

I suspect you are right that Low X count is more due to wind reading, the last 6 months i have seen a big improvement in this area but im still in my relatively early days. plus Lower Light is a bitch of a range in the afternoon when we shoot. ](*,)

v63800
Posts: 82
Joined: Mon May 16, 2016 2:56 pm

Re: Effects of changing neck tension

#23 Postby v63800 » Sat May 13, 2017 8:44 pm

good advice from memilanuk, those fullbores don't mind jumping .045 - .050


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