Fiddling w/ neck tension...

[memilanuk]

Hello,

In past I've usually gotten 'good enough' results from loading up a dummy round, clapping a dial caliper on it and selecting a bushing thats 0.003" under that reading... enough neck tension to keep things from moving, but not so much as to make the expander ball work the neck too hard and pull things out of place. This time around I've got an itch to fiddle a litte bit w/ the neck tension. I've done it before, but not in anything really resembling a defined and methodical process. FWIW, I'm using Redding Competition seater and Type 'S' F/L bushing dies w/ the floating carbide expander ball.

Re-checked a load I worked up this spring for the .243 Win: 115gr DTAC, 47.5gr H1000, neck-turned Winchester case, 215M primer. Played w/ seating depth the other day, and went from 0.020" off to 0.015" in,relative to the 'jam' reading w/ my Stoney Point tool). Groups went from scattered and strung kinda vertical,0.020" off) to a neat round hole .3-.4" in size at jam length, to a literal horizontal line across the aim point as approached 0.015" into the lands. Kind of cool to watch in progress!

Question is... am I correct in supposing that neck tension is the next correct parameter to mess with here in hopes of shrinking the group size a bit more? I have neck bushings several thou below and above the current size that I'm using,.268")... nice having L.E. Wilson Tool & Die just the next town over

Thanks,

Monte

 

[jb1000br]

Monte -- I have not seen a need to play much...what I start with is usu. what i stick with.

did 1/2 a thou...to sensitive for me

did 2.5 thou...too much for me,bullet scarring)

try to stay 1-1.5 thou right now...and alter other things...if you shot a horizontal line, the load is probably OK...I would shoot it at distance...anything under 1/2 MOA of vertical should be competetive most times...but 1/4MOA is nice when it happens,my 6BR regularly holds this at 500yds with 5-shot test groups...and i haven't seen it go OVER 1/2MOA except when I had carbon buildup issues)

JB

 

[Clarence]

Monte:
Ponder this statement. If you are backed out of the Lands ya probably need more tension due to the possability of distorting the TIR, and if you use too much neck tension and you are using the Redding die you will not get the good TIR. less neck tension equates to better TIR out of the die.
If one spends much money at the Chamber why NOT let it do the work by seating the bullet long and let the $5,000 chamber seat the bullet, one is advised to reduce the tension to somewhere arround .0015.

Clarence

 

[memilanuk]

Hmmm.... well, I can certainly go that route as well. I was kind of surprised w/ how flat those groups were w/ the bullet seated long... most definitely wasn't wind! I'll have to pull the expander ball off to let the bushings do all the work. Normally I have left it in there just to make sure any slightly dinged case mouths get ironed out... not shooting BR here so every once in a while a case gets away & hits the ground on the firing line.

The 'jam length' setting I use is seated pretty firmly into the lands... i.e. it won't go no more w/ ordinary hand pressure using the Stoney Point tool. I'll lighten up the neck tension a bit... from 0.003 down to 0.002 or 0.001 and vary the seating depth a bit as well. Hopefully I find the 'magic combo' pretty quickly... don't want to waste too much of what is probably a somewhat limited barrel life!

Thanks,

Monte

 

[overbore]

Sir, Following my own advice which is "as a last resort read the instructions" Reding says that " Brass spring-back_, neck ) is 0.001"-- so if you use a One thou bushing and it springs back that much, you have just wasted money on a good bushing for no gain in tension other than, no expander ball) the tension of your tight chamber neck, IMHO> Overbore

 

[jb1000br]

OB -- there is really no constant springback. IME, the more you move the brass in one step. the more it will spring back.

With my old 6.5-284:

loaded round: .2912
bushing: .291 letters down
Diameter out of bushing: .2905-.2907
fired diameter: .293

almost ZERO springback,moving it less than 3thou), as i got dead on .2910 when the bushing was used correctly "letters up" and ~half-a-thou less when inverted.

JB