As I try to refine my brass processing techniques, I am trying to understand some measurements I'm seeing. I use an RCBS case master to measure runout on my case necks. I am seeing .006"+ on some PMC brass. Now I've read that your runout measurement should be divided in half. Is this true? If so, can someone please explain why? Do I really have .006" or .003" runout?
Understanding case neck runout
- Thread starter Sgt_Jamez
- Start date
Re: Understanding case neck runout
The confusion is the two different ways of reading it..
There is TIR (total indicated runout)
And just 'Runout' (or actual runout)
Imagine your case neck to be crooked by .003"
So your needle reads +.003 on the high side, and then drops to
-.003 on the low side.
The needle has moved .006" in TOTAL (TIR)
But the neck is only off by .003" (actual runout)
The confusion is the two different ways of reading it..
There is TIR (total indicated runout)
And just 'Runout' (or actual runout)
Imagine your case neck to be crooked by .003"
So your needle reads +.003 on the high side, and then drops to
-.003 on the low side.
The needle has moved .006" in TOTAL (TIR)
But the neck is only off by .003" (actual runout)
Re: Understanding case neck runout
Ah ok. So what I've been doing is zeroing the dial on one side's max deflection and measuring the other max. So .000" to .006" is really .003" Got it.
Separate question if you don't mind... is there brass out there that is inherently flawed and can't have it's runout removed? I'm trying to understand if my process is inducing (or at least not correcting) runout, or that the practice brass I'm working on just plain sucks and can't be straightened.
Ah ok. So what I've been doing is zeroing the dial on one side's max deflection and measuring the other max. So .000" to .006" is really .003" Got it.
Separate question if you don't mind... is there brass out there that is inherently flawed and can't have it's runout removed? I'm trying to understand if my process is inducing (or at least not correcting) runout, or that the practice brass I'm working on just plain sucks and can't be straightened.
Re: Understanding case neck runout
When are you measuring your brass? Try measuring after firing and then look at it after sizing to see how much runout you are inducing through your technique. Freshly fired brass should be pretty straight. It is usually after sizing that things go to pot. Then you have bullet runout that either happened with crooked brass from sizing or from seating or even from uneven neck wall thickness.
When are you measuring your brass? Try measuring after firing and then look at it after sizing to see how much runout you are inducing through your technique. Freshly fired brass should be pretty straight. It is usually after sizing that things go to pot. Then you have bullet runout that either happened with crooked brass from sizing or from seating or even from uneven neck wall thickness.
Re: Understanding case neck runout
I bought the K&M neck turning gear and was practicing on some pickup range brass. I FL sized it, expanded, turned, and then neck sized. THEN measured. Most of it had that 0-6 runout.
I bought the K&M neck turning gear and was practicing on some pickup range brass. I FL sized it, expanded, turned, and then neck sized. THEN measured. Most of it had that 0-6 runout.
Re: Understanding case neck runout
You need to shoot it after turning, measure case neck runout at that point, and then perform your usual sizing operations and see what it looks like.
Neck turning will not really help case neck runout. It will aid in bullet runout, but only after the brass has been fireformed after turning. That pushes the imperfections to the inside.
You need to shoot it after turning, measure case neck runout at that point, and then perform your usual sizing operations and see what it looks like.
Neck turning will not really help case neck runout. It will aid in bullet runout, but only after the brass has been fireformed after turning. That pushes the imperfections to the inside.
Re: Understanding case neck runout
I have asked the same question about runout. It seems that industry standards dictate that it is the total deviation as upposed to half of that which to me is the truer measurement.
Very little runout may be due to deviation in neck thickness. There should be a minumal amount on a fired case, but after sizing, most is due to lack of lube in the neck and general poor resizing methods
For the record, .006 is too much.
I have asked the same question about runout. It seems that industry standards dictate that it is the total deviation as upposed to half of that which to me is the truer measurement.
Very little runout may be due to deviation in neck thickness. There should be a minumal amount on a fired case, but after sizing, most is due to lack of lube in the neck and general poor resizing methods
For the record, .006 is too much.
