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Case Neck Run Out
Posted: Mon Jul 22, 2013 3:21 pm
by Stuck
Hi all,
I've just been having a read into measuring case neck run out & I'm a little confused.
Whilst I can see the point in measuring such a thing I'm not sure what you would do with such information, is this just a measure of how accurate your dies are or does this then lead to another process to correct the run out?
Thanks,
Mick.
Re: Case Neck Run Out
Posted: Mon Jul 22, 2013 5:13 pm
by meles meles
Ah, these modern cartridge thingies, far too complex, they'll never catch on...
*Dreams of the halcyon days of pouring powder down the barrel, ramming home a lead ball (or , in extremis, a pebble) and then stuffing a match down t' hole *
Re: Case Neck Run Out
Posted: Mon Jul 22, 2013 6:24 pm
by The Gun Pimp
Stuck wrote:Hi all,
I've just been having a read into measuring case neck run out & I'm a little confused.
Whilst I can see the point in measuring such a thing I'm not sure what you would do with such information, is this just a measure of how accurate your dies are or does this then lead to another process to correct the run out?
Thanks,
Mick.
Well Mick, it's all to do with launching your bullet as 'centrally' as possible up the bore - desirable if you are intent on hitting what you aim at. Hopefully, your dies will be producing straight(ish) rounds and you can assess this by measuring run-out - of the brass and the seated bullet - with a concentricity gauge. If you are not producing straight rounds, you might want to look at some better dies.
Anticipating your next question - "How much difference will it make?" Hard to say but, if you are using a custom rifle with match barrel etc. shooting 'straight' rounds will certainly make a difference to group size.
Re: Case Neck Run Out
Posted: Mon Jul 22, 2013 6:31 pm
by meles meles
But won't the rounds self centre in the bore as they travel up the barrel ?
Re: Case Neck Run Out
Posted: Mon Jul 22, 2013 7:02 pm
by whoowhoop
I have developed the affectation of rotating each loaded round by about a guessed 120% on seating the bullet to try to improve the concentricity.
Not that it would make a difference to either my shooting or the quality of the ammunition.
Re: Case Neck Run Out
Posted: Mon Jul 22, 2013 10:37 pm
by The Gun Pimp
meles meles wrote:But won't the rounds self centre in the bore as they travel up the barrel ?
No - as I say, pick up some fired bullets and look at the rifling marks. You will occasionally find bullets with marks visibly longer on one side than the other.
Re: Case Neck Run Out
Posted: Thu Jul 25, 2013 6:20 pm
by Maggot
It can also have something to do with the thickness of the necks.
As they are stamped out of the blank, cases can be slightly thicker on one side which means that when fired the whole thing flexes a bit odd and is a bit out of kilter.
That said, I would imagine that any out slight out of round would be sorted on the first firing as it is swaged at "Kerist knows how many PSI" against the chamber etc.
I saw G David Tub was marking his so they were always in the same place in the chamber.
I have neck turned, but I think that helps equalise neck tension by equalising wall thickness more than anything, but then followed by a damned good wallop....
Checking all this is one thing I will have to get round to one day, but I am currently too lazy and more worried about wind reading TBH