Possible runout caused by chamber?

[1811shooter]

Hey guys. I’ve been lurking here for a couple years and taken in a lot of great knowledge since then. I finally have a dilemma I can’t cure with the search function so here it goes.

I recently got a Sinclair concentricity gauge and have been messing around with bullet and case runout on my .308. I’m having a hell of a time trying to get my bullet runout within an acceptable range. So far i seem to be averaging between .003 a .005. I’m using Nosler brass that how now been twice fired in my rifle and neck sized only with a Lee Collet die. I haven’t needed to bump the shoulders yet though I’m sure I will in the next firing or two. The bullet is a 178 grain ELD-X. I am seating with a Forster seating die and loading on a Hornady LNL AP progressive. I realize the progressive isn’t ideal for precision loading but I can’t imagine this being the culprit as the press has been surprisingly precise in all other measures.

I have tried partial seating and rotating and seating the rest of the way, which did not seem to improve anything. I know I am using the gauge correctly. I took some factory hornady match ammo and was able to measure less than .001 of runout.

I have also tried turning my necks which does not seem to offer any improvement to bullet runout.

Next I took a sharpie and marked the high point on the bullet on a handful of loaded rounds. After that I took the same rounds and measured the high point of the necks. I found that the high points of the necks and bullets were always 180 degrees apart, never 90, 45, etc.... given that this brass is twice fired from my rifle I concluded that perhaps there is something wrong with my chamber since each round must be coming out slightly banana shaped, though I have no idea how I would measure this, or how a chamber reamer could even make a banana shaped cut.

The rifle is an off the shelf Bergara Premier series HMR, which is supposed to be on par with their custom line as far as quality goes.

 

[Richard Coody]

Simply check concentricity on a piece.of your fired brass. Fired.and unsized.brass is the best it will ever be. Check again after sizing. Then after seating. That way you identify where runout is being introduced.

 

[1811shooter]

Simply check concentricity on a piece.of your fired brass. Fired.and unsized.brass is the best it will ever be. Check again after sizing. Then after seating. That way you identify where runout is being introduced.

That is what I have done. I have not full length or body sized the brass at all. I don’t have any fired brass that haven’t been ran through my collet die but I will check that too after my next trip to the range.

Is there a way to set up a Lee collet die so badly that it could induce that much runout? I have followed the at length instructions for setting the die up that are floating around this forum somewhere and I am getting exactly the neck tension I’m aiming for.

 

[divingin]

Is there a way to set up a Lee collet die so badly that it could induce that much runout?

I think that before you obsess too much over the possibility of an incorrect setup of your die, it would make sense to verify what is actually causing the problem.

Fire a few rounds in your rifle, measure runout. Do your first step, recheck runout. Continue on through your entire process, checking after each step.

You'll figure out what step is causing the runout, and you can exert your effort on the actual problem, rather than trying to hypothesize on correcting things that aren't a problem.

 

[Richard Coody]

.003 runout is perfectly acceptable unless your rifle is consistently shooting groups less than quarter moa.

Most.find the lee collet die loads very concentric ammo. Simple.setup. lots of.utube videos. You might try the o ring under your die trick.

 

[243winxb]

Add a Reddng body die to the process. Or better, a Redding type S fl bushing die. Dont use bushing with Lee collet neck die.

Use the Lee to size the neck.

 

[jepp2]

So far i seem to be averaging between .003 a .005.

Is that runout or TIR?
Since you are using a LCD to size these, you are discounting the "bumps" the LCD leaves, right?

 

[chop house]

+1 on @Richard Coody comments.

FWIW i have, to myself, repeatedly demonstrated that the lee tapered expander induces less runout than either a 'standard' or elliptical button no matter how they are utilized. it does, however, require a two step process using first a fl die (no expander) and then expansion on the upstroke using a donor .44mag lee die body as a holder for the expansion mandrel.

i have a full complement of LCDs and body dies that do not get used as often now that i stumbled on this method.

 

[1811shooter]

I think that before you obsess too much over the possibility of an incorrect setup of your die, it would make sense to verify what is actually causing the problem.

Fire a few rounds in your rifle, measure runout. Do your first step, recheck runout. Continue on through your entire process, checking after each step.

You'll figure out what step is causing the runout, and you can exert your effort on the actual problem, rather than trying to hypothesize on correcting things that aren't a problem.

I guess I'll have to wait until after the next range trip to measure brass straight from the chamber. I'll report back then. Thanks.

.003 runout is perfectly acceptable unless your rifle is consistently shooting groups less than quarter moa.

Most.find the lee collet die loads very concentric ammo. Simple.setup. lots of.utube videos. You might try the o ring under your die trick.

I will look into that. I'm assuming there is more to it than just using the Lee o-ring dies that come with it?

Add a Reddng body die to the process. Or better, a Redding type S fl bushing die. Dont use bushing with Lee collet neck die.

Use the Lee to size the neck.

This is my plan at least. I have a redding body die, I just have not used it yet as I haven't felt any appreciable resistance on the bolt handle closing yet.

Is that runout or TIR?
Since you are using a LCD to size these, you are discounting the "bumps" the LCD leaves, right?

I'm not familiar with TIR, if you could explain. Are you referring to the effect the gaps between the collet fingers have on the case neck? I don't believe those account for the larger swings in run out as they don't appear as sharp spikes on the gauge, rather more line a sine wave would if charted on paper.

I am measuring bullet run out at the shoulder of the bullet, just where the bearing surface begins. I'm measuring neck run out just half way between the case mouth and neck/shoulder junction.

 

[jepp2]

I'm not familiar with TIR

TIR is total indicated runout. So if your need lowest reading is 0.014" and the highest reading is 0.020", then your TIR is 0.006". Your actual runout is 1/2 the TIR, so it would be 0.003" in this example.

Are you referring to the effect the gaps between the collet fingers have on the case neck?

Yes, those are the "bumps" I mentioned. It just makes it much harder to get an accurate reading as the indicator is jumping over the high spots.

 

[Straightshooter1]

Yes, those are the "bumps" I mentioned. It just makes it much harder to get an accurate reading as the indicator is jumping over the high spots.

Just to reiterate the solution to this, that bumpiness goes goes away, for the most part) if one runs two cycles of the press on the case and turning the case around 1/8 turn for the second one so that those little "bumps" are mashed down. Then, if one wants an even smoother reading, just do a couple twists of the neck in some steel wool.

TIR is total indicated runout. So if your need lowest reading is 0.014" and the highest reading is 0.020", then your TIR is 0.006". Your actual runout is 1/2 the TIR, so it would be 0.003" in this example.

BTW, I've always wondered if the typical reference (especially in this forum) to "runout" is the TIR or the "actual runout"???

 

[1811shooter]

TIR is total indicated runout. So if your need lowest reading is 0.014" and the highest reading is 0.020", then your TIR is 0.006". Your actual runout is 1/2 the TIR, so it would be 0.003" in this example.

Yes, those are the "bumps" I mentioned. It just makes it much harder to get an accurate reading as the indicator is jumping over the high spots.

Ah, I understand. I have been zeroing the gauge at the lowest point and taking the measurement at the highest point for each round. I realize that does nothing to compare consistency from round to round, but I'd been using it as a simple way to determine the total runout for each round.

Just to reiterate the solution to this, that bumpiness goes goes away, for the most part) if one runs two cycles of the press on the case and turning the case around 1/8 turn for the second one so that those little "bumps" are mashed down. Then, if one wants an even smoother reading, just do a couple twists of the neck in some steel wool.

BTW, I've always wondered if the typical reference (especially in this forum) to "runout" is the TIR or the "actual runout"???

I have done this before, but it didn't seem to me that the bumps would have any significant impact on accuracy. I have not seriously tested this though.

 

[Murray Brook]

@divingin gave you good info. Do as he says and find out where in your process that the run-out is coming from. Then you can deal with what is causing it.. JMO

 

[Straightshooter1]

I have done this before, but it didn't seem to me that the bumps would have any significant impact on accuracy. I have not seriously tested this though.

I've not tested it either. It's the inside of the neck that's important as that's where the bullet is making contact.

And if there is any effect, I'm sure the little bumps have much less effect than neck thickness variances that have been moved to the outside.

 

[Uncle Ed]

A case can warp when fired and the smaller the case diameter in relation to chamber diameter the more the case can warp.

And when you spin the case on the case body to check runout and if the case body is egg shaped you will read runout that is not in the neck or bullet.

NECO Case Gauge
https://www.neconos.com/item/Concentricity-Wall-Thickness-and-Runout-Gauge-12
The NECO, patented, Case Gauge is the most versatile instrument available for measuring the various accuracy determining factors of cartridge cases, bullets and loaded ammunition. No other gauge can measure all of the following: 1.Banana curvature of case. 2.Wall and neck thickness variations. 3.Case head squareness. 4.Banana curvature and out-of-round shape of individual bullets. 5.Runout of seated bullet. 6.Total runout of loaded cartridge.

Bottom line I collected "old" milsurp rifles and many of them had out of round chambers. And this could be caused during war time chambering or by the armourers using sanding sticks to remove rust in the chamber. So yes you "might" have a defective chamber but warped cases with an unequal case wall thickness can warp, become egg shaped and show runout that isn't caused by the case neck. And you can find this by putting the gauge on the case body and spinning the case. And if you full length resize the case and the case body is not touching the chamber walls it will not push the bullet out of alignment with the axis of the bore. And the Late Jim Hull of Sierra bullets made a very funny but accurate statement about full length resizing.
"The cartridge should fit the chamber like a rat turd in a violin case."

I have both gauges pictured below and the Hornady gauge holds the case like it would be held in the chamber. Meaning by the bolt face in the rear and by the bullet in the throat. And the problem with this type gauge is you can not check case neck runout after sizing before bullet seating. Meaning this type gauge is not what you need to troubleshoot a runout problem.

Below German Salazar is answering a question about "partial full length resizing" and "NOT reducing the case body as much as normal.

The Rifleman's Journal
Germán A. Salazar

"a full-length sized case in which the neck is also fully sized. There is clearance at the neck and in the body of the case, the closest fit anywhere is the bullet in the throat. If the neck to bullet concentricity is good (although it needn't be perfect), then the bullet will find good alignment in the throat and the case body and neck will have minimal influence. Let's not forget that the base of the case is supported by the bolt face or the extractor to a certain degree as well; this is yet another influence on alignment. As you can see, there are several points from base to bullet that can have an effect. My procedure is to minimize the influence of those that I can control, namely the case body and neck, and let the alignment be dictated by the fit of the bullet in the throat and to some extent by the bolt's support of the base. Barring a seriously out of square case head, I don't think the bolt can have a negative effect on alignment, only a slightly positive effect from minimizing "case droop" in the chamber. Given that a resized case will usually have a maximum of 0.001" diametrical clearance at the web, this isn't much of a factor anyway.

In conclusion, I believe that allowing the bullet to find a relatively stress-free alignment in the throat by full length sizing (including the neck) and turning necks to enhance concentricity gives the bullet the best probability of a well-aligned start into the rifling."

 

[1811shooter]

Thanks Uncle Ed and everyone else. Being that the brass is only twice fired Nosler brass I'd be surprised to learn if it had bad enough thickness issues throughout the whole batch to cause that, though it does seem more plausible than a banana shaped chamber on a not-so-cheap over the counter rifle. I'm going to try and get some more range time in the next few days and hopefully find some answers.

 

[Dusty Stevens]

If you get a tubing micrometer and measure the neck thickness around the case youll see where its coming from

 

[Uncle Ed]

If you get a tubing micrometer and measure the neck thickness around the case youll see where its coming from

Dusty, I thought you used Redding bushing dies.

Tech Line & Tips (FAQs)
Concentricity & Bushing Dies
https://www.redding-reloading.com/tech-line-a-tips-faqs/142-concentricity-a-bushing-dies

To create precision reloads, you must start with cases of good quality. They should all be from the same manufacturer and lot number. A good measure of case quality is how uniform the neck wall thickness is. Cases with uniform neck wall thickness, will be of uniform thickness all the way to the base. This is important for accuracy, as the cases will expand uniformly upon firing, and contract uniformly when sized. Neck turning helps, but it's only a partial cure, as you can't turn the case wall all the way to the base. The Redding Case Neck Gauge is the preferred instrument for checking neck wall thickness and uniformity. Also note that the concentricity of a fired case only indicates how concentric your firearm's chamber is. It provides you with little or no information on the quality of the cases you're using.

Dusty, below is my favorite gauge for checking case neck uniformity, and my ball mic is seldom used.

And a case neck like on the right below isn't worth turning or getting a ball mic out of its box.

NOTICE, no ball micrometers were hurt or injured during the filming of this posting.

 

[Dusty Stevens]

Dusty, I thought you used Redding bushing dies.

Tech Line & Tips (FAQs)
Concentricity & Bushing Dies
https://www.redding-reloading.com/tech-line-a-tips-faqs/142-concentricity-a-bushing-dies

To create precision reloads, you must start with cases of good quality. They should all be from the same manufacturer and lot number. A good measure of case quality is how uniform the neck wall thickness is. Cases with uniform neck wall thickness, will be of uniform thickness all the way to the base. This is important for accuracy, as the cases will expand uniformly upon firing, and contract uniformly when sized. Neck turning helps, but it's only a partial cure, as you can't turn the case wall all the way to the base. The Redding Case Neck Gauge is the preferred instrument for checking neck wall thickness and uniformity. Also note that the concentricity of a fired case only indicates how concentric your firearm's chamber is. It provides you with little or no information on the quality of the cases you're using.

Dusty, below is my favorite gauge for checking case neck uniformity, and my ball mic is seldom used.

And a case neck like on the right below isn't worth turning or getting a ball mic out of its box.

NOTICE, no ball micrometers were hurt or injured during the filming of this posting.

As long as you measure em thats all that matters. That rig will show you how much you need to turn them then you can get out the tubing mic to hit the tenth if it matters in your particular shooting style

 

[1811shooter]

I have a ball micrometer and have turned the necks but so far it doesn’t seem to be a neck thickness issue.