BS-Concentricity

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  • Last Post 20 August 2018
joeb33050 posted this 11 August 2018

 

Concentricity

 

Concentricity, sometimes called coaxially, is a tolerance that controls the central axis of the referenced feature, to a datum axis. The axes for the datum and referenced feature are derived from the median points of the part or feature. Concentricity is a very complex feature because it relies on measurements from a derived axis as opposed tangible surface or feature.

 

Threshold: If it don’t look crooked, it’s fine.

 

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pat i. posted this 20 August 2018

"Now that's an offer I can refuse."

LOL. Guess that just about says it all and exactly the answer I expected. Have to admit it was pretty funny though.

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45 2.1 posted this 20 August 2018

Since you claim to be a CBA member all you have to do is shoot in a registered match to show everyone you're right. I'm going to quote Ed Harris: "I have learned a few things over the years, and will share, but feel free to ignore me, I really don't care." If you are interested enough in my CBA membership, you can ask David Reiss since he handled my last 5 year re-up. Your results will be posted in the FS for all to see. Ill even make the 200 mile drive to Windhill rannge to introduce you around. Now that's an offer I can refuse. Its not that hard and you get to show a better way. And who the heck uses microfilm anymore?

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pat i. posted this 20 August 2018

Since you claim to be a CBA member all you have to do is shoot in a registered match to show everyone you're right. Your results will be posted in the FS for all to see. Ill even make the 200 mile drive to Windhill rannge to introduce you around. Its not that hard and you get to show a better way. And who the heck uses microfilm anymore?

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45 2.1 posted this 20 August 2018

You're making a lot of assumptions as to what CBA guys do or are using. Your profile says you're a CBA member...don't you read the match reports and data? I have since about issue #12, mostly hard bullets..... show me otherwise. Can you think of a better fit than a bullet tapered or bumped in a die made from the same reamer as the barrel was throated with sized a half thousandth under ballseat diameter? Yes, I can, but my examples aren't special case. If so I'd like to hear about it. Made by M P Molds as he produces a majority of bullets that shoot very well. If the nose of a 2 diameter bullet shows signs of rifling marks on the nose when chambered it will be guided as well as any design in a standard chamber and throat. I don't agree, but you shoot what you want. If you look on the net, you'll find videos of bullets exiting the muzzle... just before that exit you'll usually see a jet of dirty high velocity gas coming out. Somewhere along the way the base has gas coming around it and that shows it is unsupported (that has to happen before the bullet bearing body seals the bore at the throat) with the one point of contact you've said and probably one side of the base since an unsupported bullet will kick sideways (unless it is toleranced tightly to the chamber neck) and not remain in line with the bore center . If it isn't guided well it will not enter the rifling concentrically...... thus the normal 1 MOA + or - groups. Getting one to fit is a trick sometimes but the design itself isn't the problem. Again we don't agree and group sizes show which is better.... smaller groups = better design. Personally I've never shot a linotype bullet always going with WWs heat treated or not but have shot enough matches with people that were using linotype to KNOW there's nothing wrong with it. Again, show me those consistent great groups showing nothing is wrong. I can read the record groups also and I don't see anything that can't be done with a lot softer alloy. As far as the matches you shot 35 years ago, in the internet age it might be possible to look up the information. Maybe at their office on microfilm (sp), but not on the net. If you could give me the clubs that hosted the matches and the newspapers that carried the results we might find them. I have a great nephew who's a computer wiz and can find anything.

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pat i. posted this 20 August 2018

You're making a lot of assumptions as to what CBA guys do or are using. Your profile says you're a CBA member...don't you read the match reports and data? Can you think of a better fit than a bullet tapered or bumped in a die made from the same reamer as the barrel was throated with sized a half thousandth under ballseat diameter? If so I'd like to hear about it. If the nose of a 2 diameter bullet shows signs of rifling marks on the nose when chambered it will be guided as well as any design in a standard chamber and throat. Getting one to fit is a trick sometimes but the design itself isn't the problem. Personally I've never shot a linotype bullet always going with WWs heat treated or not but have shot enough matches with people that were using linotype to KNOW there's nothing wrong with it. As far as the matches you shot 35 years ago, in the internet age it might be possible to look up the information. If you could give me the clubs that hosted the matches and the newspapers that carried the results we might find them. I have a great nephew who's a computer wiz and can find anything.

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Ken Campbell Iowa posted this 20 August 2018

testing ammo ... hah...  trying to be the best that ever was ... my buddy 22 rf competitor and i took two bricks ( 1000 rounds ) of exquisite midas L ( $400 in today's dollar ) and measured half of each brick to the half thousandth ...  the other half we left in the boxes .....we then shot it all up with two good match rifles in an indoor 50 yard bench range.

We learned that to a 70 per cent certainty that 22 rf  midas L shoots better right out of the box than carefully sorted to a half thousandth.

i plink a lot since those days .  measuring 30 carbine loads shows no advantage either ...

ken

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45 2.1 posted this 20 August 2018

Sizing to maximum headspace only works if the head-to-datum dimension is a crush-fit, otherwise the differential in body diameters will enable the round to be cocked and misaligned by pressure of the plunger ejector.  My method seems to work for me over the long hall, I've been using it since 1983. Something which is also a factor is whether the rounds are bent in stripping from the magazine and chambering during the feed cycle of a slam-feeder such as a Garand or M14. There are other semi-auto rifles out there other than the Garand and M1A that aren't all that hard on cartridges. I'm not talking about jacketed either. I'm only interested in results of cast in these rifles. Cast and jacketed are as different as night and day in them.

All my experience in this regard is with Match-conditioned Garands in both cal. .30 and 7.62mm, and M14NM rifles shooting Lake City arsenal loaded M72 and M118 Match ammo selected from lots selected as being "statistically average" having a 600 yard acceptance test Mean Radius of 2.4 to 2.6 inches. 

Tests I did at MCDEC for Maj. Bruce M. Wincentsen were to inspect and separate 100 rounds each of LC M72, M118 and M852 Match ammo which indicated 0.0015" TIR or less. The case heads were indexed using a felt-tip pen mark from 12:00 to 6:00 between the "LC" and the year date of the headstamp. The test rounds were then  oriented and inserted into a magazine and another round placed on top of them. The top first round was fired, while the marked and indexed round was extracted without firing and spun again.  Bottom line, the carefully selected "straight" arsenal rounds were "bent" from 0.003 to 0.005 during the semi-auto feed cycle. 

This was in M14s.  Back to 600 yards there wasn't any difference worth the trouble. 

I quite tongue-in-cheek suggested building a fixture which would uniformly "bend" the rounds consistently to 0.010" TIR and mark the bullets for orientation. Then we should repeat the slam feed test, to see chambering the bent rounds would "straighten" them.  Then, of course we would have to shoot the bent and oriented rounds at 600 yards.  Mark Humphreville and Larry Moore laughed out loud, but I wasn't joking.  No better way to "kill the monkey" and stop the nonsense.

I think they were afraid that uniformly bent and oriented rounds they might actually shoot better...

Good information........................

 

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45 2.1 posted this 20 August 2018

What is "dynamic fit" Keeping or having the bullet itself keep in line with the throat into the rifling ahnd how do you achieve it By picking a bullet that fits the throat in your rifle so it can line up as it goes forward? What is it you think CBA members are doing wrong and why you think your way is better? Shooting hard two diameter Barlow inspired designs and loading methodology. I compare group sizes, less is better. When you say "normal" group size what are you talking about? Whatever is normal for the class you shoot in (production, hunter, heavy etc.) Is it the groups shot by the various classes in the BR match program? Military match program? People writing about shooting a 7mm Mauser or in the case of an ongoing thread the 303 British? What is "written in stone" in CBA channels? Most of you guys write about linotype and shooting at MOA plus or minus. You've said many times before you used to shoot in matches, non CBA if I remembers right although in one case you told me you shot CBA matches, but got bored with it. That's about right. Thats understandable but can you tell me what organization was hosting the matches and point me to where I can see the results? Those clubs are gone now and the results are buried in 35 year old newspapers. At that time we had a league sponsoring matches in the lower half of our state. Thanks for the reply and information I asked for in advance.

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Ed Harris posted this 20 August 2018

Sizing to maximum headspace only works if the head-to-datum dimension is a crush-fit, otherwise the differential in body diameters will enable the round to be cocked and misaligned by pressure of the plunger ejector.  Something which is also a factor is whether the rounds are bent in stripping from the magazine and chambering during the feed cycle of a slam-feeder such as a Garand or M14.

All my experience in this regard is with Match-conditioned Garands in both cal. .30 and 7.62mm, and M14NM rifles shooting Lake City arsenal loaded M72 and M118 Match ammo selected from lots selected as being "statistically average" having a 600 yard acceptance test Mean Radius of 2.4 to 2.6 inches. 

Tests I did at MCDEC for Maj. Bruce M. Wincentsen were to inspect and separate 100 rounds each of LC M72, M118 and M852 Match ammo which indicated 0.0015" TIR or less. The case heads were indexed using a felt-tip pen mark from 12:00 to 6:00 between the "LC" and the year date of the headstamp. The test rounds were then  oriented and inserted into a magazine and another round placed on top of them. The top first round was fired, while the marked and indexed round was extracted without firing and spun again.  Bottom line, the carefully selected "straight" arsenal rounds were "bent" from 0.003 to 0.005 during the semi-auto feed cycle. 

This was in M14s.  Back to 600 yards there wasn't any difference worth the trouble. 

I quite tongue-in-cheek suggested building a fixture which would uniformly "bend" the rounds consistently to 0.010" TIR and mark the bullets for orientation. Then we should repeat the slam feed test, to see chambering the bent rounds would "straighten" them.  Then, of course we would have to shoot the bent and oriented rounds at 600 yards.  Mark Humphreville and Larry Moore laughed out loud, but I wasn't joking.  No better way to "kill the monkey" and stop the nonsense.

I think they were afraid that uniformly bent and oriented rounds they might actually shoot better...

 

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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pat i. posted this 20 August 2018

What is "dynamic fit" and how do you achieve it? What is it you think CBA members are doing wrong and why you think your way is better? When you say "normal" group size what are you talking about? Is it the groups shot by the various classes in the BR match program? Military match program? People writing about shooting a 7mm Mauser or in the case of an ongoing thread the 303 British? What is "written in stone" in CBA channels? You've said many times before you used to shoot in matches, non CBA if I remembers right although in one case you told me you shot CBA matches, but got bored with it. Thats understandable but can you tell me what organization was hosting the matches and point me to where I can see the results? Thanks for the reply and information I asked for in advance.

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45 2.1 posted this 19 August 2018

However, I believe that the above is mostly mental masturbation, because if the case is not fire-formed to fit the chamber, a case which is not tight fit will lay low in the chamber or be forced off-center due to pressure exerted by the plunger ejector of a Garand, M14 or M16.
There are other ways...................... Like sizing to maximum headspace among other factors.

If bullets are seated out long, so as to engage thee origin of rifling, AND the rounds are concentric, then the cartridge is aligned by the bullet fit in the throat.  This is how benchrest shooters do it, and also how our most successful cast bullet shooters do it.  

Static fit seems to work fine until you look at the normal group size. However there is another way and that involves dynamic fit which can give better results if you don't pollute the method with what is now written in stone in CBA channels.

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Ed Harris posted this 19 August 2018

Ammunition which indicates less than 0.0015 TIR was felt by the military rifle teams and Palma Team members to be used at 1000 yards.

Ammo which was up to 0.003" TIR was felt fine back to 600.

Ammo greater than 0.003" TIR was used for 200 and 300 rapid.

However, I believe that the above is mostly mental masturbation, because if the case is not fire-formed to fit the chamber, a case which is not tight fit will lay low in the chamber or be forced off-center due to pressure exerted by the plunger ejector of a Garand, M14 or M16.  The Brits, Aussies and Canadians took their ammo straight from the box, didn't spin it, crack the black Lucas seal and reseat or any of that stuff that Mid Tompkins, Clint Fowler, Larry Moore or Mark Humphreville were inclined to do.  AND they cleaned our clocks repeatedly.

If bullets are seated out long, so as to engage thee origin of rifling, AND the rounds are concentric, then the cartridge is aligned by the bullet fit in the throat.  This is how benchrest shooters do it, and also how our most successful cast bullet shooters do it.  

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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Shopdog posted this 14 August 2018

This whole line of reasoning,"BS" this is flawed from the get go from my perspective,but that's me.

Just remember, not every action you take is self actualizing,often a handloading chore is a setup or foundation for other specific goals.By getting the areas of your handloading isolated,that are causing excessive run out you're opening up a door to testing possibly,more important issues at hand.

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Geargnasher posted this 12 August 2018

So, we should redefine the question.

Concentricity of loaded cartridge with itself, and chamber body/neck/leade with the bore.

In possibly another category, whether or not the chamber and bore axes are colinear.

Since we're quantifying these things relative to group size, I'll submit that colinear axes within as much as 12-15 thousandths can still shoot repeatable 5/8", 5-shot groups with ammunition which passes a visual test involving rolling across a flat surface with no detectable runout; whether or not such a crooked chamber will actually shoot well is entirely dependent on loading technique and component choice. However, a throat which has as little as .002" axial misalingnment with the bore, as measured from an impact impression with a concentricity gauge, isn't likely to shoot very well, in my experience that falls soundly into the 1.5 to 2 moa category at the very best.

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Larry Gibson posted this 12 August 2018

I also agree with Ric......in some cases concentricity does matter.

LMG

Concealment is not cover.........

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RicinYakima posted this 12 August 2018

Ken, That is not how I measure it. A well oiled case is fired in the chamber and fully fire formed. It is placed on two bearings one ahead of the extractor cut and one just behind the shoulder. Dial indicator goes on the case neck. I measure the run out of the chamber, not the ammo. Many chambers will give you a run out of over 0.002".

Or you can make a good chamber cast, or pound cast, and measure the leade in the barrel in relationship to the chamber. 0.010" is very common on commercial rifles.

From my testing of 15 years ago on '03 Springfields, if the ammo is straighter than the chamber, orienting doesn't help. But if the ammo is not straighter than the chamber, orienting does help. Good clean tools and workmanship allows you to make better ammo than the barrel and you don't have to worry about this.

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Ken Campbell Iowa posted this 12 August 2018

as a machinist, a thousandths of an inch is a mile ...

but still my obsessive mj benchrest buddies tell me they can't detect any group improvements under about 0.002 runout in bullet relative to a perfect case .....  and i think i could see 0.002 runout ... so:

looks like    joeb might be correct ...   

with a slight reserve that we gots mushy castings, not mj bullets.  could be that mj bullets are somewhat self-healing , and lead isn't .  there are copper springs ..... there are no lead springs ... 

ken

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Ross Smith posted this 12 August 2018

I think that this goes hand in hand with the case and bullet orientation.

That means I agree with joe.

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R. Dupraz posted this 11 August 2018

Yup!

 

R

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frnkeore posted this 11 August 2018

Agreed, Ric.

Frank

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