Bullet runout - what's acceptable/normal?

[ShootingNewbie]

Howdy. I've been reloading for about 6-7 years now, and decided to start looking at runout/concentricity in my loaded rounds, measuring at both the neck, and near the pointy end of the projectile.

The tool I'm using to measure looks something like the Sinclair one (ht tps://www.sinclairintl.com/reloading-equipment/measuring-tools/concentricity-gauges/sinclair-concentricity-gauge-prod37479.aspx), and seems to give pretty repeatable results - i.e. if I measure a round a few times, it's pretty much the same each time, and different rounds will give differing results, so I think I trust it.

What I'm finding is that if I measure loaded rounds at the neck, I'm pretty consistently at about 1 to maybe 2 thou of total needle movement, but if I measure closer to the tip of the projectile, I'm (sometimes) getting a lot more - 4 to 5 thou with some rounds. (This is happening with both .223 and 6BR rounds, btw.)

Dies: I'm using a Redding full-length bushing die for .223, a Redding competition bushing neck die for 6BR, and Redding competition seating dies for both 223 and 6BR.

Other misc. info: necks are turned, brass is Nosler (.223) and Lapua (6BR), and projectiles are Sierra MatchKings (.223) and Berger (6BR).

Questions:
- am I likely correct in thinking that the runout is related to the seating operation, since the runout at the neck appear to be acceptably low?
- is this amount of runout worth worrying about? (I shoot strictly at paper, but want nice small groups on that paper...)

Any thoughts would be appreciated - thanks!

 

[rral22]

How bad are your loads shooting? Why do you think runout is an important issue for your loads that you need to address now? If I had that level of runout I would likely ignore it and look first to several other variables if I was trying to shrink group size. I'm not sure that you can ever consistently achieve zero runout, or that it is worth the effort to try, so .....

 

[bigedp51]

I have the two concentricity gauges pictured below and they measure the runout two different ways.

The top image below is how the Hornady gauge measures the bullet runout and the bottom image is how your gauge and the majority of runout gauges work. Meaning the Hornady gauge holds and rotates the case by the rim and bullet tip. And the other type gauges spin the case on the body of the cartridge and measure the runout.

And as you can see in the bottom image the closer to the bullet tip you measure the more runout you will have. Normally you measure the bullet runout just forward of the case neck, and this tells you how straight the case neck and bullet are in relation to the axis of the bore.

I measure the case neck thickness variations with a Redding neck thickness gauge pictured below. Then after full length sizing using the dies expander I measure the case neck runout and subtract the neck thickness variations. This tells me if I'm doing anything wrong when sizing and if the die is inducing neck runout.

Below is a Redding bushing die and the area between the red lines is not sized by the bushing. Also note the gap or air space along the sides of the bushing and die body. The gap allows the bushing to float, "BUT" the bushing can move from side to side and even tilt when sizing the case neck. The Redding bushing FAQ tells you when reducing the neck diameter .004 or more it can induce neck runout. And if the neck thickness varies .002 or more you use a bushing that reduces the neck diameter .004 and use the dies expander to push the neck variations to the outside of the case neck. This same bushing FAQ tells you when reducing the neck diameter .004 or more to reduce the diameter in two steps to help reduce neck runout. Remember the bushing floats and can move from side to side and even tilt when sizing the neck that can induce neck runout.

The U.S. Military considers match grade ammunition to have .003 or less neck runout. And at the Whidden custom die website they tell you they get more concentric ammunition using non-bushing full length dies. I get less neck runout with Forster full length dies than with bushing dies and off the shelf factory rifles. NOTE, the reason so many reloaders use the Lee collet die with a Redding body die is because they get less runout than with a bushing die

Bushing dies work best with tight neck chambers with neck turned brass. And with factory rifles with SAAMI chambers that let the case neck expand .004 or more with unturned necks the runout can increase.

 

[bigedp51]

How bad are your loads shooting? Why do you think runout is an important issue for your loads that you need to address now? If I had that level of runout I would likely ignore it and look first to several other variables if I was trying to shrink group size. I'm not sure that you can ever consistently achieve zero runout, or that it is worth the effort to try, so .....

Basically a runout gauge tells you if the runout happens during sizing or bullet seating, meaning where the runout problem starts.

And the main cause of neck runout happens if the expander is locked down off center, or if the seater plug allows the bullet to tilt. Or if the bushing moves or tilts during sizing due to the amount of diameter reduction and neck thickness variations. I have had new Remington .223 cases with .009 neck thickness variations that will cause concentricity problems with a bushing die.

Below is a Lee full length die and the expander is held and centered by the locking collet, meaning you can not mess up and lock the expander down off center. And the average reloader "without" a runout gauge who full length resizes would be better off with a cheaper Lee die.

Below is a Forster full length benchrest die with their high mounted floating expander. The case neck is held and centered in the neck of the die when the expander enters the case neck. And this method produces cases with little to no neck runout.

Below the Forster and Redding benchrest seating dies hold the case and bullet in perfect alignment and can even slightly correct any neck runout.

Below the 6.5 Guys tell you they have less neck runout with non-bushing Forster die than with a Redding type S bushing die.

 

[ShootingNewbie]

rral22, biged - thanks for the replies.

rral22: re: how bad/why do you think: they're shooting pretty decently currently (@100 yards, the .223 groups pretty consistently in 3/8" to 1/2", and the 6BR does a bit better), but there's always room to improve somewhere.

biged: I've got a tool equivalent to the Redding neck thickness gauge in post #3, above, but I've not looked at variations in wall thickness for a while; the next time the cases are empty (i.e. I've found time to get to the range and fire them...) I'll put a good portion of the various batches thru the gauge and report back.

If the US Army considers .0003 runout at the neck acceptable for match grade ammo, then I may be in better shape than I had thought?

Thanks again!

 

[209jones]

Nice explanation there Big Ed, well done.

 

[bigedp51]

Below is from the now shutdown The Rifleman's Journal website by the competitive shooter German Salazar. He is answering a question about "Partial Full Length Resizing" when the case body is not reduced in diameter as much as full length resizing. What he is saying below is when the case body is reduce in diameter by full length resizing it has very little to no effect on bullet alignment with the axis of the bore.

The late Jim Hull of the Sierra ballistic test lab and competitive shooter had a humorous saying about full length resizing. "The cartridge should fit the chamber like a rat turd in a violin case".

Below Mr. Salazar explains how a full length resized case should fit the chamber. And if you read between the lines a full length resized case body and neck do not touch the chamber walls. Meaning it reduces the effects of neck runout because the case body and neck have chamber clearance and less guiding effect on the bullet.

"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."

The Rifleman's Journal
Germán A. Salazar


NOTE, the American military considers match grade ammunition to have .003 or less bullet runout. And this is good enough for off the shelf factory rifles and the amount of runout becomes more critical with tight chambered custom rifles.

Below the case shoulder with a full length resized case is the only part of the case touching the chamber. And as long as the case does not warp the first time it is fired and the case body does not touch the chamber walls the case has wiggle room in the chamber. (rat turd in a violin case)