concentricity issues?

[jump70]

I'm currently shooting a 6XC in f-class club comp. Chamber has a neck about 0.275" and I'm shooting 105gr Lapua Scenars over 38.4gr of 2209, CCI BR primer and 1st Gen Norma brass, which turn to about .013", giving me a loaded round diameter of approx 0.269"

I FL size with an FL bushing die, using a .267" neck bushing. Both fired and sized cases (using this die) are very concentric, with TIR about .001" or often less at shoulder/body junction and neck, using sinclair concentricity gauge.

Where things get a bit weird is when I seat bullets - also using a Neil Jones custom threaded micrometer seater. When I measure TIR on tbe seated bullet - just shy of the ogive, it blows out to about .004"-.005". I note the odd difference in apparent seating force required but the runout variance is across the board.

Does anyone have any suggestions on what the problem might be or what I might try to remedy things? My thought was that maybe sizing down about .008" in one step might be creating some issues but again - the concentricity tool seems to indicate not.

Press is a forster co-ax and shellholder has no problem - clearly no issues here given no runout issue when sizing.

Any ideas?

Thanks, Justin

[AlanF]

Justin,

Most of it could be that any neck runout will be magnified as you measure further out on the projectile. Try marking the neck on max runout side before you do the seating, then see if the seated projectile max runout is on the same side.

One way of reducing neck runout is to do your sizing 3 times rotating a third of a turn between each. It was suggested to me by Bill Shehane, and it definitely helps.

Regardless of the above advice, from what I have read, 0.005" runout is nothing to worry about.

Alan

[jump70]

Alan

Thanks for your advice - all seems to make good sense.

I'll try all your suggestions and try not to sweat it too much. I've just had a case of the weirds over this runout issue as I've seen the odd inexplicable flyer lately and I've been wondering if the two things were inter-related. Probably not...

[pjifl]

I wouldNOT consider 0.005 thou runout to be nothing to worry about.

But I do not think you can consider runout in isolation.

In a sloppy chamber with oodles of neck space 0.005 may not make things any worse but with minimum spec chambers I believe 3 thou should be considered a max.

Peter Smith.

[AlanF]

Peter,

My statement was in regard to projectile runout, not neck runout. The balance of opinon on benchrest.com is that 0.005" projectile runout is okay. My impression is that some top BR shooters don't even bother to check it.

Alan

[jump70]

I went back to some of my loaded rounds and measured the runout on the bearing surface of the seated projectile, as opposed to further towards the ogive. I noted runout of 0.001" to 0.003" as an extreme spread.

I also noted that neck concentricity on the sized/loaded cases are running about the same. This is opposed to fired case neck runout of less than <0.001".

Something going on in the seating operation, either that or I've just hit the limit of the dies and my reloading techniques...

[pjifl]

A lot of benchrest loading uses fairly loosely seated bullets run into the lands. And many boast that weighing powder is a waste of time.

But I think this fails when applied to extreme range shooting ???

Depending on how close to the lands the bullet is, a well seated off centre bullet can pull the neck into tighter contact on one side. I believe some velocity measurements I once did showed an increase of velocity because of this.

Not sure if it is noticeable on the target but I feel a lot better if I can test concentricity to better. than this.

Peter Smith.

[jump70]

changes in neck tension causes velocity to differ and this certainly sticks out at long range in terms of vertical dispersion.

i start to get hives when i see an unexplained flyer that doesn't appear to have been caused by a shooting stuff-up by yours truly or some weird wind change..

[ned kelly]

G'Day All,
as a SR BR shooter, I do not weigh powder, I do not own a concentricity guage, use 0.002" neck tension and seat 'em 0.020" into the lands and if I get 3 shots cutting each other at 200yds with stuff all vertical in the group, then I'm good to go, just got to worry about the wind........

However, in F class, I weigh each LR load carefully and I am seriously considering getting a concentricity guage, meplat trimmer and sorting bullets. Whether this is all needed out to 600 yds who knows but I reckon it is a good idea beyond that.

If your measuring the point on the bullet where the parallel section tapers to the tip I would naturally expect variation, especially in mass produced bullets. Why else do LR BR shooters sort their bullets...variation in the pointing dies, jacket material, and hardness etc, etc.

If there is no run out in the parallel section/bearing surface of a known quality bullet and you are using quality sizing dies and a straight line seating die (preferably a wilson style die) I would have no reason to expect the run out to be excessive ie.> 0.003" (take with a grain of salt as I cannot measure anything at this stage! )

Alternatively you could try rotating the case 3-4 times while operating the ram full stroke to seat the bullet, ensuring the bullet is seated as truely as possible into each case. Whether this helps, i do not know but it should ensure there is no bias on the bullet from the seating die.

Anyway, the proof of a good load and loading process is usually how the rifle shoots, if the level of accuracy delivered on target is what is expected given the condition of the bore and what the prevailing wind conditions allow, then reasonably that is all you can expect from the rifle/shooter/conditions combination

Just my 2 cents!

Cheerio Ned

[pjifl]

Some more thoughts on this.

I am sure much is conjecture because it is so hard to prove anything. We need a few donated barrels to shoot out and a 1000 yd long warehouse....

I have reservations on the amount of improvement from multiple seating at different angular settings.

I believe most of the problems go back to the case quality. If a bullet has been seated a little out of line and it is reseated at a different angular setting, there is probably enough spring such that the bullet will not be repositioned unless it is very badly out of line. I once bent back into line some badly eccentric cartridges in a controlled way and was a little surprised at how much springback there was. By the way I dont think bending back is a very good solution. I tried multiple seating - both full depth first go - also progressive seating each time - and never saw much improvement with either.

Similar with inline dies. I am not knocking them in any way - just that bad brass used with an inline die can still deliver an out of line projectile.
I did some experiments (some unintended) which seems to verify this.
Maybe this explains gains some have from annealing necks while others see no advantage.

I think some concentricity measurements have helped me understand in a limited way what was happening during reloading.


A difference between BR and F is that F requires a lot more cases. So you cannot have your dozen perfect pet cases which always perform for each shoot. This may be another reason to look at concentricity more in F shooting.

Peter Smith.

[ned kelly]

G'Day Pete,
another reason you probably need concentric cases is with BR any error in case/ammo quality is not readily obvious. magnify the distance from 200ys to 600-1000yds and any mechanical errors in case/ammo are obvious. Much the same way MV becomes a critical issue at the longs.

Just reading about Bill Shehane in "Precision Shooting at 1000yds" he uses custom FLS die to just "massage" the case to 1-2thou each time and uses a standard wilson seater die blank reamed out with his chambering reamer to give him 0.0005" run out. He prefers no more than 0.001" to shoot BR at 1000yds........Must work for him!

Hope this helps,

Cheerio Ned

[a.JR]

Hrs,,

[RDavies]

I have been trying to get the concentricity of my 7mm down below .005" runout and yesterday found the reason why bullet runout was so far out (ranging from .005-.012+").
I found the tip of the bullet was bottoming out on the end of the seater stem on the seater die.
You might want to check that your bullet tips arent bottoming out on your seater die.

[a.JR]

e]

[bruce moulds]

jeff,
you have no idea how glad i was to hear your percentages of runout with home made dies.
i am happy with 0.015 max in a batch, and have given up trying to improve on that for fclass.
observations would suggest that minimizing runout is a sizing issue more than a seating issue if all is well with the seating die, and assuming necks are concentric.
rounds loaded in new brass often have0.005 to 0.008 runout, and will waterline 2/3 of the 10 ring comfottably if load and bullet in relation to leade is correct.
there are other things that also cause elevation, like bending light, and wind, that are probably more important to an fclass shooter than runout up to a certain ammount. how many of us can absolutely guarantee our scales? meplat diams?
testing in mirage time of the year can be very disillusioning!
my fclass rifle can hold less than 0.2 moa elevation for 15 shots at 300, but it is very hard to duplicate that or come close at longer ranges with the same consistency, because there is more to go wrong between you & the target.
bruce.