Effects of changing neck tension

[Jase PTRC]

My F Std rifle shoots quite well, Im using Lapua Brass with a light skim taken off the necks with 46.1gr of 2208 which was determined by a ladder test cci450 primers and 155.5 full bore bergers seated .010 off the lands. Although it holds well into the six ring i would like to try to get a better X count. My question is could going to a tighter neck (e.g. .001 tighter) improve vertical spread? or should i be looking at changing something else.

[watrob]

Hi, I do not shoot F Std but in general I would suspect that if you are .010" off the lands and you increase neck tension you would increase pressure slightly which in turn changes FPS and effects your tune, whether this increases or decreases vertical would need to be tested?

You say you did a ladder test, in this test did you also test the 155gr bullets at different seating depths other than .010" off?

If your test confirmed .010" off the lands was the most accurate this may now change if you apply more neck tension?

Are you using Lapua large rifle primers? if so try the Lapua small rifle primer cases, the SD average tends to be lower with these cases?

Also, have you checked the SD of your current loads, if there is a large SD spread this would also count for your vertical?

And finally, if you have vertical you may not yet have the perfect tune due to the above factors, also what neck clearance are you allowing, is the chamber SAAMI or Match grade?

All you can do is re-test with the adjustments you make, but applying more neck tension it will change your load and you may or may not have to drop .1 or .2 of a grain of powder to come back into tune?

[Jase PTRC]

I have tried shooting them from .020 and also .015 off the lands and found .010 to be the best. when i say vertical spread im meaning inside the 6 ring last weekend at 300 mtrs i shot 57.3 and 59.2 with the dropped shots being windy ones so not terrible by any means but lower X count than i would like. I am using Palma small primer cases already. My chamber is a .340 Neck and my cases are necked using a .336 bushing. Just looking at things to change one at a time and see what happens. I have never fiddled with neck tension so i dont have the experience to know what might happen hence why i am asking here for some feed back from people who might have tested this.

[watrob]

What brand/type of primers are you using?

If you are necking done to .336" and after the projectile is loaded what is your finally neck size? if its .338 you should try .003" not .002" neck clearance?

I run my cases so they only expand .001" when the projectile is inserted as I jam .010", this way they all seat at the same depth (push method), I have .003" neck clearance to neck chamber?

Also what is your trim case length compared to your actual chamber ( not what the book says), always had to measure the neck length as they are never what the gunsmith says, they are always several thou out. I run at about .004 trim case length to my actual chamber.

[Jase PTRC]

My loaded round neck size is .337. Which gives me .0015 neck expansion or .003 clearance as my chanber is a .340 neck.. Im wondering if going slighly tighter eith a .335 bushing would give more consistent neck tension than what i have now. Im using cci450 small rifle magnum primers as i mentioned earlier

[watrob]

.003" clearance is ok, but I would change to BR4 primers, 46.1gr of powder is not a lot and the BR4 will give you better SD. I run the same case fire-formed to 7-08ai with 48 grs of 2209 and changing to BR4's gave me better groups.

[Jase PTRC]

I have some Br4's at home so will try them next and then i will play with neck tension after that. I haven't had anyone plot for me yet so will get that done this week before i change anything.

[aaronraad]

My loaded round neck size is .337. Which gives me .0015 neck expansion or .003 clearance as my chanber is a .340 neck.. Im wondering if going slighly tighter eith a .335 bushing would give more consistent neck tension than what i have now. Im using cci450 small rifle magnum primers as i mentioned earlier

more consistent neck tension - if you need more, how much more consistent than you are getting currently? Are you seating with something like the K&M Arbor Press with force dial indicator or some other gauge to tell what's going on?

It's hard to talk about neck tension without also talking about neck thickness - Accurateshooter.com - Neck Tension — Not Just Bushing Size

It's BR and hasn't been peer reviewed, but Jack Neary can handload if you want to talk about 0.002" OD clearances. Just note the thin BR neck thickness though! - Target Shooter Magazine - TUNING THE 6 PPC RIFLE FOR BENCHREST COMPETITION BY JAMES MOCK

This is why holding tolerances during neck turning is important and becomes such a PIA that "no-turn neck" chamberings are so likable.

[Jase PTRC]

if you need more, how much more consistent than you are getting currently? Are you seating with something like the K&M Arbor Press with force dial indicator or some other gauge to tell what's going on?

Unfortunately i don't have the equipment to measure or test seating force. Im using an RCBS Rock chucker with a competition seating die. My question regarding consistency was more to ask if going a little tighter (.002) would likely improve any variation in tension if there were very tiny fluctuations in neck thickness or projectile diameter over only going .001

It's hard to talk about neck tension without also talking about neck thickness

My necks are turned on a 21st century lathe with a TiN cutter but only sufficiently to make them uniform not to a specific size, also neck thickness is not something i am able to measure with the gear i have. (In my opinion this can only be done with a ball gauge micrometer not vernier calipers)

It's BR and hasn't been peer reviewed, but Jack Neary can handload if you want to talk about 0.002" OD clearances. Just note the thin BR neck thickness though! - Target Shooter Magazine - TUNING THE 6 PPC RIFLE FOR BENCHREST COMPETITION BY JAMES MOCK

This is why holding tolerances during neck turning is important and becomes such a PIA that "no-turn neck" chamberings are so likable.

I agree with this and my chamber at .340 is classed as a no turn chamber. But running my Lapua cases at a light skim the first turn through the neck turner revealed that factory neck thickness leaves me feeling like regardless how good their product is the variation in 1 batch i wasnt happy to leave them unturned. Will post a pic shortly.

[Jase PTRC]

Screenshot_20170228-144356.png

These were turned again after this to remove any spots that got missed.

[aaronraad]

These were turned again after this to remove any spots that got missed.

Did you mandrel expand prior to skim turning?

[Jase PTRC]

Yes i did

[plumbs7]

Hi Jase , keep neck tension around 2.5 -3 thou and this will improve ignition. Also try br 4 and 46.6 2208 155's hybrid or full bore 5 thou jump or 3 thou jammed !

Chrony your load to see if it's consistent? You could also have your optimal barrel timing /barrel exit harmonics wrong too? Eg bullet is exiting just before and at the top ( or bottom) of the mode 1 harmonics? Eg negative compensating?

Annealing is important too!
Regards Graham.

[Jase PTRC]

Hi Jase , keep neck tension around 2.5 -3 thou and this will improve ignition. Also try br 4 and 46.6 2208 155's hybrid or full bore 5 thou jump or 3 thou jammed !

Chrony your load to see if it's consistent? You could also have your optimal barrel timing /barrel exit harmonics wrong too? Eg bullet is exiting just before and at the top ( or bottom) of the mode 1 harmonics? Eg negative compensating?

Annealing is important too!
Regards Graham.

Thanks Graham, after i get my plots from this weekend i plan on running another ladder test. Barrel has 600 rounds on it now so its probably due to re check the tune. im not too fussed about running it hotter, i did have a higher node on the initial ladder but didnt think it was necessary to go that far. (higher node was at 46.7) Your info on ignition vs Neck tension is helpfull and i will try it. i have never been too keen on Jamming but i guess it cant hurt to try it.

So question is now where to start? Should i try Primers first? This is my first purpose built rifle and the first time i have done load development so any guidance would be help full. cheers.

[Matt P]

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. 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". 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. 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