concentricity gauges etc

[Chanonry]

Guys,intriguing though it might be how much initial non concentricity might be reduced (probably not all) by the bullet being almost swaged thought the bore...and some very exaggerated drawings of bullets yawing wildly down the bore,these are not meassured effects.

 

The question is not about 'fuzzy lumps' gyrating haphazardly through the air( I am happy to accept rifles outshoot muskets) but rather whether an incease in measured concentricity from 3 thou to 1 thou is going to make a measureable difference on target.

Several posters seem to have done the comparison-and are less than convinced.

20 thou to two thou might.....data would be nice.

Who calibrates the concentricity guages...are they as (un) reliable as say chronos,or better....

Anybody checked factory ammo of only modest concentricity and compared it on target with otherwise very similar ammo (same bullet,etc)-though it will be ver difficult to control all the differences with only concentricity differing.

 

 

Just to see where I coming from,if it seems implausible-of the top 100 PRS shooters in US (first shot hits on 1-2 moa targets from 200-1200 yards,real life positional and some awkward), only a very few were loading powder by volume,but the rest were about equally split (48 to 47 approx) in using .001 powder scales or .1 powder scales...that is a "huge' difference (x100 precision) but apparently half didn't think it very important....and these are very good shooters.....

 

Maybe a very slight bend in go fast stripes does not affect performance (other than very,very slightly....).

 

:-)

 

gbal

 

George

 

Did an experiment once with a 270 that was driving me up the wall with erratic groups. I sorted 50 cartridges by concentricity. Sadly I discovered that reloading the 270 was highly inconsistent. I had lots <=2thou but I also had a lot around 10 thou. Shot on a rest. Guess what 10 thou were all over the place, but the low concentricity were sub 0.5. Not sensational but this a shitty Steyr hunting rifle we are talking about.

 

I have never been able to see the difference below the 2 thou level but that is probably because those variances are swamped by larger errors elsewhere in the total system - mainly my shooting.

 

I have to say I am a fan of a concentricity gauge. Given my background, it struck me that without one it is not possible to implement proper QA/QC to the reloading process. My approach was to measure at each stage in the process to assess the repeatability of each stage. That was very effective as it highlighted when I was producing shite and what steps were to blame. I could then work on that stage until I had it taped. For me, that is the real benefit to a new reloader - it gives meaningful feedback.

 

After that I just batch check. Other wise we are making the rookie error of assuming everything will be fine.

 

So ideally borrow one for a while

[srvet]

But what if the chamber is non concentric as I suspect many are. Let's say the chamber is 10 thou out of true and you load a round that is also 10 thou out. Depending on the orientation of the cartridge in the chamber, could the bullet could end up between 0 and 20 thou out in reference to the bore?

[gbal]

srvet; without saying I think it correct/plausible etc,this rather harks back to Creighton Audette's 'banana' brass issue,which has been mentioned in two recent other posts....CA was a very respected wildcatter and sensible experimenter in the early days,and ahead of his time in attempting measurement...

He claimed some early brass had systemic faults that misaligned bullets with respect to concentricity. He marked such suspects wrt chamber orientation (ink spot at 6oclock when chambered,and if they were flyers,claimed he could reload and predict the direscton of the flyer and control it by realigning appropriately in the chamber next firing.

Not much heard about now-brass is so much better-can't see boxes of Lapua with a thin section down their entire length!

As indicated,the idea was not much investigated otherwise,probably because the problem was soon much reduced by better brass. Chambers may be another matter. But what you suggest ,was claimed to be more or less so by Audette...

It would not be hard to mark flyers with ink before removal,and check them again after reloading-as do some US shooters-if flyer repeated they simply ditch the brass....seems sensible,if not explanatory!

 

gbal

[gbal]

Chanonry,

Thank you for your informed post,with some relevant data.

We seem on the same page wrt new reloaders. Quality control checks are always desireable where practicable/affordable in the reloading process. Bullet concentricity guages do that rather well for bullet seating (though not it's depth-that will need other comparator and micrometer tools-and,please no COAL-whose only use is to show if a loaded round will fit a magazine-another story).

If runout is excessive,some remedial work is indicated.

But what is excessive- I suggested 2 thou was pretty good,and your data,and others,seems to agree...and you found 10 thou was poor in your 270...no surprise. Perhaps careful reloaders don't often get much bigger runouts-but we seem to be homing in on certainly more than a few thou as a something to be checked-of course by firing a group. As I implied,such a test -holes on paper-is the only valid test of dispersal of bullets. SDs in double figures,etc etc often have an effect,but not always,and effects may be small-enough to bother the top competitive shooter,or diligent accurist,but unlikely to result in field misses (a lot of us shoot fields!)

It's also quite likely all this is as usual different for different bullets,cartridges,calibres and individual rifles.

 

As with the new alcohol consumption advice,best is none at all.Any consumption increases risk.Probably so with reloading precision too.

 

My synoptic point - was that even if a measured difference is found using reliable instruments,it may not really be a valid measure of group dispersal- or at least as you say,it's effect is so small that it is lost in the greater noise of other variables.

Hence my example of powder measurement- some have super lab class Sartorius scientifics (.001g,ie sliced up kernel) others do as well with the more usual .1g balance beams....in that discipline. (none use budget bullets,though-Bergers are the boys,a price deemed worth paying). Of course,it is likely that such preferences are in small part influnced by costs,and by the shooters individual ideas/personality/mental game.That matters a bit,when prcision and accuracy reach very high levels all round.There may be a small edge advantage...at least in the mind...

 

Nothing at all new-I recall being amazed at the care taken by the early benchresters,yet the apparently cavalier lapses of a few (the great Warren Page simply did not clean primer pockets,but did OK). Cleaning brass is equally 'divisive'-perhaps even more so today. Absolutely fine-as an atheist I do not feel compelled to put it in second place. But it is 'hells own business' to showa consistent advantage frrom one detailed process over another-feel good factor,of course,actual score advantage consistently....hmmmm

 

OK good measures of concentricity are helpful,sometimes diagnostic tools that help fine tune ammo,and can identify an aberrant batch,so if it performs poorly,it won't be a surprise. Competition shooters 'need ' that safety net.

We can't yet be very precise about how many thou is tolerable-indeed it is very likely a risk factor issue,but there is little need for any remedial action with 2 thou...10 thou might raise eyebrows and merit a test group....

 

Concentricity measures may vary-are they cross calibrated/compared?!

 

Much mayhem has arisen from the assumption that all chronos are reliable AND valid.Not so,as many posts here attest..so the rookie reloader should bear that in mind-only reliable and valid measures are worthwhile,anything else is actually potentially negative (you wrongly think you know your velocities).

 

And sometimes an imperfection (3 thou run out,powder 'only' .05 g consistent) does not mean a duff group...as it gets bigger,it might.....and eventually will (check your barn door sizes too) :-)

 

"Good enough" is a pragmatic compromise.

 

gbal

[1066]

This sounds as if we're making a bit of progress here. A little run-out, say, 2-3 thou doesn't seem to be too much of a problem but 10+ thou might be.

Good reloading practices with proper case preparation, reasonable quality components and tools will usually produce ammunition with acceptable run-out.

 

Some form of measuring concentricity is desirable as a quality control measure, just to ensure that the rest of the process is continuing to perform to the required standard.

 

I don't think calibration of the gauge is a problem. The gauges mostly use a commercial dial indicator, either plunger or finger type, even a cheap Chinese indicator will indicate accurately enough - we are really looking for a difference rather than an exact figure - a simple check with a short cylindrical length of 8mm brass rod should indicate zero.

[onehole]

Perhaps a generalisation ,,,runout/concentricity,as I see it,,,,Benchrest,,,,nil to 2/3 tenths,,,,,"Accurate" Target" a few tenths to 2 thou max,,,,,General Target,,,,,2 to 4 thou,,,,,Plinking/speed shooting 5 thou++.........I would say that any bending or forcing of ammo to achieve concentricity is probably not the way forward,,,something is still bent really is,nt it?........O

[gbal]

OK-seems that a couple of thou runout,at least,is no real cause for despair...pragmatically.

 

I note there isn't really that much clear data correlating run out with bullet dispersal...at very low run outs it's probably not reliably measureable anyhow...

 

Throw this in....Does group size matter? ( actually it's a 'risk' factor (ie larger group more risk of miss) so a rather better question is "How much does group size matter/"

 

Well,maybe not at all stricty for the cold bore one off hunter/precisionist.One shot isn't a group!

 

But if we look at a WEZ analysis of 'hit probability' then perhaps another perspective emerges:

 

(under identical shooting scenario conditions,specifying shooter skill/load/environment,data for 6.5 Creedmore):

 

The hit probability on a 20 inch target at 1000y for a .1 moa rig is 70.4%

 

The hit probability on a 20 inch target at 1000y for a 1 moa rig is 75.4%

 

Put another way,the inherent precision of rifle can only be one of many factors determining accuracy at long range,though it is a major factor determing accuracy at short range. (at 100 yards the .1 moa rifle will hit a fly many times more often than the 1 moa rifle!). But at 1000y and 20 inch target,it's only 5% better.

 

Note-these are decent sample probability stats- if we fire 100 shots,on average we can expect 70/71 and 75/76 hits respectively....actual first hit probability will be similar,for example-probably a hit (low 71-75%)-there is not a lot of difference ( ie gives the Ruger PR a good chance,IF all else equal,as it did with the Savage,as long as 5% don't separate the best scores.......but when it does, then there is no cheap lunch!)

Changing the shooting assumptions-otherwise held equal,while moa varies above-gives the effects of each variable-from SDvelocity/shooter ability/range estimation/BC etc etc. eg lesser BC bullets will not achieve the above 70-75 % ,but the general small advantage of the more precise rig will be preserved. Shooter wind error remains the major factor under almost all scenarios.

 

 

 

Interesting.....of course much shooting is between these given short and long ranges,so don't throw away your tack driver. Ask rather, "Is plus/minus .1 moa,or 1thou run out,or 20 fps...etc...a game changer for MY game?"

For most,the answer will be probably not.

 

gbal

[Chanonry]

 

 

Interesting.....of course much shooting is between these given short and long ranges,so don't throw away your tack driver. Ask rather, "Is plus/minus .1 moa,or 1thou run out,or 20 fps...etc...a game changer for MY game?"

 

 

Exactly. The delight of WEZ analysis is that it shows how small the effects are of tight 'tolerances'. If expressed as a Hit % or a scoring projection they are invariably consumed by the shooters errors of position or wind compensation certainly for all but the best shooters.

 

It is an illuminating analytical. I ran a comparison of shooting a 260 vs 308 both with modern bullets and loads to see whether it was worth changing the barrel on the AI. I used realistic data (not fanboy data) and made some assumptions specific to what I do with a rifle. For me the difference in hit percentage seemed to be about 3-5%. Also for me, that was not worth the cost. For others, 200 yards further out and in a serious competitive environment the answer would have been different.

 

I do think capturing data is worthwhile even if it may not be strictly correct in an absolute sense, as we can relate performance over a period of time to this data. if performance degrades or data points move we can understand this and adjust accordingly.

 

There comes a point where the dominant error is elsewhere in the system and it is time to focus on that if further improvement is required, rather than wasting further effort on the last variable. Depends on the standard that is being sought.

[gbal]

Today's Accurate Shooter bulletin repeats this tip for improving bullet runout,easily and maybe ("Rotate case during seating" :

 

When seating the bullet (arbor or screwin seater) seat bullet half way,then rotate bullet 180 degrees,and finish seating. Sometimes helps reduce runout,and is quick and easy-in this example ,run out reduced on average from .00228 to .00148.

 

(And no,I don't know if doing it in four 90 degree turns is better,or....just try the 180..... :-)

 

There is also a link to the Forum discussion "How much runout is acceptable" which if nothing else gives a flavour of the diverse opinions on run out,and the quite limited good data available-no doubt the two are related.Mostly of course the run out is already pretty good,among these shooters. It is probably of more concern if runout is ,say,greater than 5 thou....?

 

gbal

[Murph]

srvet; without saying I think it correct/plausible etc,this rather harks back to Creighton Audette's 'banana' brass issue,which has been mentioned in two recent other posts....CA was a very respected wildcatter and sensible experimenter in the early days,and ahead of his time in attempting measurement...

He claimed some early brass had systemic faults that misaligned bullets with respect to concentricity. He marked such suspects wrt chamber orientation (ink spot at 6oclock when chambered,and if they were flyers,claimed he could reload and predict the direscton of the flyer and control it by realigning appropriately in the chamber next firing.

Not much heard about now-brass is so much better-can't see boxes of Lapua with a thin section down their entire length!

As indicated,the idea was not much investigated otherwise,probably because the problem was soon much reduced by better brass. Chambers may be another matter. But what you suggest ,was claimed to be more or less so by Audette...

It would not be hard to mark flyers with ink before removal,and check them again after reloading-as do some US shooters-if flyer repeated they simply ditch the brass....seems sensible,if not explanatory!

 

 

gbal

Here's a link to a YouTube video by David tubb were he describes in detail this very thing. He marks his cases where he measures bigger wall thicknesses.

https://youtu.be/NUnrYp0NH38