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concentricity gauge indications

23 Jan 2015
@ 12:56 am (GMT)


I managed to find a second hand concentricity gauge. So iv been measuring up a storm.
So far I'm fairly happy with fired and sized cases. Some vary a bit but within spec. Iv seen a few half thou readings so I know my gauge has the tolerance in it to measure down that low. (Errors or rough spots in the gauge)
First I graded my rounds to 1.5 thou under or over. In my ammo box either good or bad.
I noticed that neck run out was on pah with projectile run out or close enough. For example the neck was measuring close enough to what the projectile was measuring.
But then I had a few that were a fair way out. Let's say the case neck was 1.5 thou but the projectile was around four thou.

So i guess this is a long winded way of asking shouldn't the fairly good neck keep the projectile on pah? As most of the rounds were. How often or likely are projectiles out of round? I know oal varies a bit. I try to keep my seating rythum the same for each round, or is the odd out of time rythum enough to see differences. I usually start seating, rotate then carry on.
Can a bad seating die show results of a good neck yet bad projectile run out? Wouldn't the neck influence the projectile?

any experiences with concentricity measurments and results welcome here.
(You knew this thread was coming didn't you nathan) haha.


23 Jan 2015
@ 01:15 am (GMT)

Mike Davis

Re: concentricity gauge indications
I have a very good mate you is really pedantic with reloading techniques (and the groups he shoots show it) who decided to run a few of my "she'll be right" reloads across his flash new concentricity gauge to see how bad they were..... .270 in mixed cases loaded at different times.... well after first dozen he gave up as they were pretty darn close to spot on........ I must have been doing something right!!!!
23 Jan 2015
@ 04:21 am (GMT)


Re: concentricity gauge indications
Hi Jason,
I use a concentricity gauge. And I have found what you are finding - that fairly straight necks at times do not give fairly straight rounds. One area that I have found decreased concentricity was how careful I was with getting the projectile straight and using a bit of graphite to lube its path into the case.

that's what worked for me anyway. And remember, its about getting it all right and being consistent.

Good luck
23 Jan 2015
@ 03:09 pm (GMT)


Re: concentricity gauge indications
Yes I kind of expected for things to be out of round by a fairly consistent amount. I try to do every round the same. Somewhere after seating things vary a bit. I would of thought if my seater is going to seat with lots of runout it would do it with all rounds not just half of them.
I guess neck turning may have something to do with it. It's really a can of worms opening.
But its part of the game we play.
I'm going into town today to get some o rings to slip under a die or two, there suppose to make the die float and self align. A cheap experiment.
23 Jan 2015
@ 03:36 pm (GMT)

Mike Davis

Re: concentricity gauge indications
the ONLY thing I do slightly different to normal is turn case/projectile 180 degrees when projectile has started to seat and continue to bottom of stroke from there.
28 Jan 2015
@ 12:34 am (GMT)


Re: concentricity gauge indications
The o rings didn't do much. I think it comes down to getting the brass neck tighter.


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