chamber and runout, concentricity

bow shot · October 5, 2009, 09:31 AM

It is unusual for brass to come out of the chamber with wacky runout?

The scenario is this:

I put some of my rounds on a v block under a dial indicator and noticed about .008" runout. I checked at the bullet very close to the brass, and on the brass very close to the bullet. That got me curious, so I took some of my recently fired spent brass and found the same thing.

Quite odd, because cartriges that I loaded in months gone by (1x fired, Lee collet neck sized) measured fantastic (hugging .001" TOL)

The questionable stuff is 3x fired Hornady brass that was just fired, and not processed in any manner there after.

Savage 12 vlp (.204 ruger)
Hornady 3x fired brass (trimmed on a Wilson)
Lee collet neck sized before firing
Previously mildly charged with Benchmark, and topped with VMaxes.
Primers still in.

SL1 · October 5, 2009, 12:18 PM

When you extract and eject the cases, do their necks strike the gun on the way out? That can bend necks and even put flat dents on the case mouths.

SL1

Shoney · October 5, 2009, 12:41 PM

Did you check the thickness of the brass at the neck?

The necks may need turning.

Slamfire · October 5, 2009, 01:38 PM

Eight thousandths chamber concentricity is awful. What sort of group size are you getting?

If the rounds come out of the chamber that far off centerline, then you have a poor chambering job.

It is a seldom recognized fact that during gundrilling, the drill bit wanders. It is not unusual for the bore to curve like an arc, sometimes a wave.

Lets say the drilled bore is an arc. You stick a straight chambering reamer in the thing, and what you get is an egg shaped chamber.

If the rifle shoots poorly, and it is under warranty, I would send it back to the factory.

bow shot · October 5, 2009, 02:11 PM

I haven't checked the thickness of the necks, I'll try to do that tonight if I can.

The cases extract very easily, no hanging or binding that I can perceive

Grouping is consistent at 0.5", even with the poor runout

So let me pose this exaggerated situation: Say I have brass that is not centric to begin with, and I fire it in a match grade barrel that is "perfect". should I expect that rifle to fire form that brass into perfect concentricity?

I'm not at all expecting that my factory Savage has a match grade chamber. But it bugs me that at one time the brass that USED to measure .001" TIR fresh from the chamber NOW measures .008" TIR out of the chamber.

I may try to get my hands on some fresh brass and do a before/after study. All I need is time and money LOL!!!!

SL1 · October 5, 2009, 07:35 PM

Bowshot,

I wasn't asking about ease of extraction. I was asking if he bullet necks get wacked against the side of the action on the way out. If you have a spring-loaded plunger type of ejector (insead of a fixed bar that rides in a slot in the bolt), it is trying to push the case to the side the whole time it is held against the bolt by the extractor. So, when the case is extracted far enoung to have the case neck clear the chamber neck, it can snap to the side against the body of the chamber, and then again it can snap against the side of the action outside the chamber as the case neck clears the chamber. Both of these bangs against the side of the gun can slightly bend a neck, either its alignment , or its roundness or both.

SL1

bow shot · October 6, 2009, 07:38 AM

SL1, understood. No, there's no situation like that. I understand what you are saying, one of my other rifles (Mauser) does exactly that.

The situation has been resolved, I found out that my dial indicator mount was loose, and I had quite a bit of pendulum motion involved. My loaded cartridges now measure .002" TIR. I haven't bothered measuring the freshly ejected brass.

Thanks very much for the assistance folks.

October 5, 2009, 09:31 AM	#1
bow shot Senior Member Join Date: March 26, 2009 Posts: 263	chamber and runout, concentricity It is unusual for brass to come out of the chamber with wacky runout? The scenario is this: I put some of my rounds on a v block under a dial indicator and noticed about .008" runout. I checked at the bullet very close to the brass, and on the brass very close to the bullet. That got me curious, so I took some of my recently fired spent brass and found the same thing. Quite odd, because cartriges that I loaded in months gone by (1x fired, Lee collet neck sized) measured fantastic (hugging .001" TOL) The questionable stuff is 3x fired Hornady brass that was just fired, and not processed in any manner there after. Savage 12 vlp (.204 ruger) Hornady 3x fired brass (trimmed on a Wilson) Lee collet neck sized before firing Previously mildly charged with Benchmark, and topped with VMaxes. Primers still in.

October 5, 2009, 12:41 PM	#3
Shoney Senior Member Join Date: February 21, 2002 Location: Transplanted from Montana Posts: 2,311	Did you check the thickness of the brass at the neck? The necks may need turning. __________________ I pledge allegiance to the Flag - - -, and to the Republic for which it stands….Our Forefathers were brilliant for giving us a Republic, not a democracy! Do you know the difference??? and WHY?http://www.wallbuilders.com/LIBissue...les.asp?id=111

October 5, 2009, 12:18 PM	#2
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	When you extract and eject the cases, do their necks strike the gun on the way out? That can bend necks and even put flat dents on the case mouths. SL1

October 5, 2009, 01:38 PM	#4
Slamfire Senior Member Join Date: May 27, 2007 Posts: 5,261	Eight thousandths chamber concentricity is awful. What sort of group size are you getting? If the rounds come out of the chamber that far off centerline, then you have a poor chambering job. It is a seldom recognized fact that during gundrilling, the drill bit wanders. It is not unusual for the bore to curve like an arc, sometimes a wave. Lets say the drilled bore is an arc. You stick a straight chambering reamer in the thing, and what you get is an egg shaped chamber. If the rifle shoots poorly, and it is under warranty, I would send it back to the factory.

October 5, 2009, 02:11 PM	#5
bow shot Senior Member Join Date: March 26, 2009 Posts: 263	I haven't checked the thickness of the necks, I'll try to do that tonight if I can. The cases extract very easily, no hanging or binding that I can perceive Grouping is consistent at 0.5", even with the poor runout So let me pose this exaggerated situation: Say I have brass that is not centric to begin with, and I fire it in a match grade barrel that is "perfect". should I expect that rifle to fire form that brass into perfect concentricity? I'm not at all expecting that my factory Savage has a match grade chamber. But it bugs me that at one time the brass that USED to measure .001" TIR fresh from the chamber NOW measures .008" TIR out of the chamber. I may try to get my hands on some fresh brass and do a before/after study. All I need is time and money LOL!!!!

October 5, 2009, 07:35 PM	#6
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	Bowshot, I wasn't asking about ease of extraction. I was asking if he bullet necks get wacked against the side of the action on the way out. If you have a spring-loaded plunger type of ejector (insead of a fixed bar that rides in a slot in the bolt), it is trying to push the case to the side the whole time it is held against the bolt by the extractor. So, when the case is extracted far enoung to have the case neck clear the chamber neck, it can snap to the side against the body of the chamber, and then again it can snap against the side of the action outside the chamber as the case neck clears the chamber. Both of these bangs against the side of the gun can slightly bend a neck, either its alignment , or its roundness or both. SL1

October 6, 2009, 07:38 AM	#7
bow shot Senior Member Join Date: March 26, 2009 Posts: 263	SL1, understood. No, there's no situation like that. I understand what you are saying, one of my other rifles (Mauser) does exactly that. The situation has been resolved, I found out that my dial indicator mount was loose, and I had quite a bit of pendulum motion involved. My loaded cartridges now measure .002" TIR. I haven't bothered measuring the freshly ejected brass. Thanks very much for the assistance folks.