Concentricity Question

[pmarauder]

So I purchased the new 21st Century Concentricity gauge, and after learning how to get the most consistant positioning for the best accuracy...... I'm learning that the inside of my necks are not as concentric as i once thought. Now for most all my brass cases (ie Lapua or Nosler) I, like most of you guys, trim to length on my wilson trimmer, run the expander mandrel through them and skim the desired amount off the necks. After this process and after firing the cases, I can measure about .0005 of run out at any point on the neck. Pretty good numbers so far. Now after measuring the inside of the necks with the new 21st century tool......(both sized and fired) I'm finding at least .0015 to .0025 of run out on any of my previous cases i thought were good to go. Hmmm. So i then measured some loaded rounds with the new tool. Case necks are good. run-out on the bullet measured at the case mouth is .0005. But as i slide the measuring needle down the bullet towards the tip, I'm getting about .0025 to .003 of runout the further out on the bullet i measure. So at this point, what are my options? Ive tried running the expander mandrel back through and "ironing" out the necks...... but i don't think that works. Ive heard that it will push the material to the outside and you can trim away again on the outside, but I'm not finding that it does this. because after running the mandrel through the inside of the neck 3 times...... I'm still getting the same reading on the inside of the neck..... and good readings on the outside of the neck. Looks like Ive opened up a Can O Worms. What are your suggestions??
Thanks

 

[spclark]

Yeah, sometimes too much information can be more trouble than not enough.

You shoot BR mostly, or score / target?

My first suggestion would be to gauge your efforts by how they affect your shooting performance. Did you acquire the new tool because you suspect non-concentric ammo (everything's relative!) is lowering your results?

I have a Sinclair gauge. Learned rounds even 0.003" out (measured where the bullets meet the lands) shoot just fine out to 1,000 yards if I break shots centered up. I don't measure many rounds much now.

 

[pmarauder]

Yeah, sometimes too much information can be more trouble than not enough.

You shoot BR mostly, or score / target?

My first suggestion would be to gauge your efforts by how they affect your shooting performance. Did you acquire the new tool because you suspect non-concentric ammo (everything's relative!) is lowering your results?

I have a Sinclair gauge. Learned rounds even 0.003" out (measured where the bullets meet the lands) shoot just fine out to 1,000 yards if I break shots centered up. I don't measure many rounds much now.

I guess im just striving for perfection..... I feel like i should be able to get tighter groups out of my 7 SAUM if my numbers were almost perfect throughout the entire loading/brass prep process. I guess im thinking that i may need to look at inside reaming of my necks. Do you feel that this would improve my inside neck run-out?
Thanks

 

[spclark]

Yes, it may, but without knowing a lot more details about your shooting habits and equipment it'd be silly to try to predict how much.

Shooting groups is another world compared to sling for score @ anything beyond 600 yards, my particular jones. A good day for me is when all my rounds for score are 'waterline' (close as possible to the widest part of the X-ring) and not outside the 10.

Some days are better than others.

Perfection's a worthy goal as long as you understand the closer you get the longer it'll take to get there in the end.

 

[fdshuster]

pmarauder: spclark covered your concerns very well, and we both agree on the area of the ogive where we take our runout readings: where the ogive meets the lands. I can also detect more R/O if I move the pointer out nearer the bullet tip, but I believe the most important point is where the bullet meets the lands.

I use .002" as a limit for match ammo, but would not feel compromised if it were .003". I've even had some excellent 5 shot groups at 1 & 200 yds. with R/O's of .005", sometimes outshooting the identical loads at those distances with R/O's of less than .003". Proving, to me at least, there are a lot of other factors at work here.

With all that being said, I do tighten up my requirements as the distances increase, needing all the help I can get out to 500 mtrs.

 

[pmarauder]

I use .002" as a limit for match ammo, but would not feel compromised if it were .003". I've even had some excellent 5 shot groups at 1 & 200 yds. with R/O's of .005", sometimes outshooting the identical loads at those distances with R/O's of less than .003". Proving, to me at least, there are a lot of other factors at work here.

Thanks for all the input.... What im trying to determine, is the root cause of the run-out. Yes, it may not matter much if im seeing .0025 of run-out on where the bullet indexes the rifling..... My closest targets are at 200 yards, and im getting some pretty good 4 and 5 shot groups. ( low .2 moa). But i think i can squeeze a little bit more accuracy out of it if everything were perfect. Maybe im overlooking something. Could the bullets themselves be a little off?? if so, what would happen?

 

[fdshuster]

Just a thought, I could be all wet. If the case neck were not truly in line with the case body, but had a slight bend in it, then might not the runout show up more the further you took the reading from the neck/shoulder junction? If it were possible to take the reading 2" in front of the bullet tip, might not the runout be even greater?

I'd hate to think the bullet ogives were not true and the tips are not centered with the body of the entire bullets' length.

 

[pmarauder]

Just a thought, I could be all wet. If the case neck were not truly in line with the case body, but had a slight bend in it, then might not the runout show up more the further you took the reading from the neck/shoulder junction? If it were possible to take the reading 2" in front of the bullet tip, might not the runout be even greater?

I'd hate to think the bullet ogives were not true and the tips are not centered with the body of the entire bullets' length.

I went back and re-measured about 20 cases on my SAUM brass at all locations on the neck as well as on the body itself. My chamber is perfect and the brass is great on the outside body and outside neck, with both fired brass and sized brass. I think i might need to closely watch the inside of my necks for run-out........ and maybe double check some of my bullets. I talked to a custom bullet maker today, and i guess its not to un-common for the bullets to get off axis due to the bullet makers press/dies having some "slop" in them due to wear. Ever look closely at the meplat tips on some VLD bullets?? they are not perfectly round, but slightly extruded to one side or the other very minutely...... That is why we trim and point. I guess its possible

 

[BoydAllen]

If your necks are properly turned to a uniform thickness, what you describe (increasing runout as you measure closer to the tip of the bullet, is a result of case necks being cocked in relation to the body of the case. The usual cause of this is the FL sizing process. I hope that you are not doing this runout measurement after expanding and turning. Expanding with a mandrel can make necks more crooked, depending on the amount of force it takes to insert the mandrel into the case neck. Check them after a couple of firings. Also, understand that you can be obsessing over something that is getting lost in the noise. IMO, when trying to improve the performance of a complex system one should fix the bigger problems first. What kind of accuracy are you getting on average, as opposed to in wallet. (Just kidding I used to carry my best groups in my wallet.)

 

[lpreddick]

would inside neck reaming reduce it's r/o measurement? my $0.04...inflation, you know.

 

[markm87]

I've even had some excellent 5 shot groups at 1 & 200 yds. with R/O's of .005", sometimes outshooting the identical loads at those distances with R/O's of less than .003". Proving, to me at least, there are a lot of other factors at work here.

We did just that.... rounded up a bunch of rounds with the most runout and shot them at a hundred.... Excited to see a big old group compared to our straight ammo......

Shot just about as good as anything else.

 

[BoydAllen]

A reamer will follow the hole. The correction that you describe (cutting the inside of the neck true to the CL of the case body) is a lot more involved and requires a lathe.

 

[bozo699]

If your necks are properly turned to a uniform thickness, what you describe (increasing runout as you measure closer to the tip of the bullet, is a result of case necks being cocked in relation to the body of the case. The usual cause of this is the FL sizing process. I hope that you are not doing this runout measurement after expanding and turning. Expanding with a mandrel can make necks more crooked, depending on the amount of force it takes to insert the mandrel into the case neck. Check them after a couple of firings. Also, understand that you can be obsessing over something that is getting lost in the noise. IMO, when trying to improve the performance of a complex system one should fix the bigger problems first. What kind of accuracy are you getting on average, as opposed to in wallet. (Just kidding I used to carry my best groups in my wallet.)

Boyd,
Didn't you and I just talk about that? LOL,..seeya, gotta go feed cattle, it's cooooold out there :
Wayne.

 

[in2deep]

As mentioned jamming an oversized mandrel through the necks may tend to bend them but it also makes you wonder that maybe some of the guys using alot of neck tension for bullet seating aren't causing similar problems and using 3 or more thou of tension combined with a less than perfect seating die fit may be cocking the necks out a little.

 

[pmarauder]

The necks are straight in relation to the bore axis and also case body. Measurements were taken off of fired brass and also sized brass. I run .002 of neck tension and used the expander mandrel after full lenght sizing. I checked the brass and it was perfect again. I ran the necks back through the sizing bushing and checked run out again on the outside..... only .0005 at the most on the neck or body of the case. My area of concern is the inside of the necks...... or possibly the bullets themselves.
Thanks for all the info though.

 

[bozo699]

pmarauder,
Thing sometimes just aren't perfect, Frank mentioned this in a earlier post,....I'd hate to think the bullet ogives were not true and the tips are not centered with the body of the entire bullets' length.
The Bearing surface should be true and should measure close to what your outside neck does but aren't 100% true, there taking a straight jacket and wrapping it around a piece of lead so to speak, as the die gets worn or debris gets in the way or any number of a 1000 other things happen may be off some, I'm not talking a lot but some. If you start a piece of tin on your roof and it's off a 1/4" 60' later the tin is hanging 2' off the roof, no different here if your case is off as near as you can tell maybe .0005 and the bullet is off a .0005 it magnifies. Check your loaded round on the bearing surface and see what you get, then go on out onto the bullet to the point it will hit the rifling's, a 6mm would be maybe .236 see what you have there, don't go any further, my bet is your numbers will be cut in half at least, try it on several random picks out of your already loaded stuff and proceed with a open mind, and I think you will see what I am saying is correct. If your necks aren't turned correctly or really aren't concentric or your into a donut then this statement would of course be void. Check some of your unloaded bullets for concentricity you might be surprised in what you find.
Wayne.

 

[pmarauder]

Guys.... thanks for all the input. Wayne....I measured the bullet at the point it contacts the lands(.277) (7SAUM) and my worst case scenario is runout of .0025. Not to bad i guess. But it is not every case. About every 4th case is out. Most are .001 or so. Here is what i think is happening...... I used 300 SAUM to make my 7SAUM by necking down. Those of you who know, My cases are now .040 short compared to actual 7SAUM brass. After 5 firings and sizing's, and after initial neck turning, I think brass is flowing somewhere...... and its doing weird things on the inside of the neck wall. My bushing die, is keeping the OD straight. But the ID....who knows. I think the extra run out on the ID is pushing the bullet this way or that. I think if i run an expander through a few times after FL sizing....and then just neck size after that...... things will be good. I cant justify spending $60 for 25 pieces of Nosler brass in the 7 SAUM. Maybe my neighbor (the blue eyed bear) has some he needs to sell at a discounted price???........Thanks for the help

 

[bozo699]

I am glad your getting it all sorted out, tell Barry I said hi and he should share his brass with a neighbor
Wayne.

 

[BoydAllen]

You might do a clean up turn at .30 cal. before you neck down. That way the brass that is moving "around the corner" ,from the repeated firings and sizings, may be more uniform in thickness. What kind of neck turner are you using, and how much shoulder bump? Also, how much are the diameters of the bodies of your cases reduced, at the shoulder and about .3 up from the head by FL sizing?

 

[halfmoanut]

My guess would be that it could possibly be coming from your die,most likely the F/L die and it would be the bushing all bushings are not created equal, after sizing with the bushing check runout on the neck only.If it is .001-.002 which is really good,then seat a bullet and see if it causes more runout,if so it is coming from your seater die. It is one of the reasons why guys use custom dies made off of the reamer your smith used to chamber your rifle with.However some brass after alot of firings will remain critical of runout no matter what is done.Match brass should be .001-.002 runout.