Bullet Concentricity/Runout

[cjc5062]

Hi all, I upgraded my whole reloading setup recently and just got everything set up. Using an Amp Annealer, Amp Arbor Press, Short Action Customs Infinity in-line Seating Die, Area 419 Zero Gen II press (for sizing), Area 419 M series FL sizing dies, Accuracy One Concentricity gauge, and Henderson Trimmer.

I'm trying to squeeze every little bit of accuracy out of my rounds. I know all this isn't necessary, but it's my hobby and I enjoy trying to chase every minuscule imperfection.

I recently loaded up some new cases (Peterson) and am not thrilled with the bullet Concentricity. I got anything from 0.001" to 0.004" on my bullet Concentricity. I anneal, full length size, trim and then seat using the arbor press and in-line seating die. For 6.5PRC I'm using the standard SAC neck guide with the M2 seating sleeve as recommended from SAC.

I believe my process is pretty dialed in, but the only thing I can think about is whether the fact I'm compressing powder for these rounds is making me get slight variations in runout? I've also measured my neck Concentricity and am getting .0005" runout on the neck, which should be great.

Appreciate any help!

 

[TaperPin]

Seating a few bullets on some empty cases should show if it’s compression related.

Good neck lube can help the bullet slide in straighter. Neo Lube painted inside the neck is known for producing the least seating pressure.

Maybe check the contact pattern of the seating stem to make sure it’s not pushing on the tip of the bullet. A seated bullet with very little runout can be painted with sharpie and run up into the seating die until it just touches the stem - the contact should be somewhat even.

It can be misleading if the concentricity gauge is set up to ride on the rim or unexpanded portion of case head, rather than body that has been sized down since it is the body that makes contact with the chamber. Unless it’s a minimal dimension small base FL die, the body will have expanded off center of the case head some amount.

To be honest, I don’t have one and use Wilson seaters, but suspect the seating die more than anything. If the base is indexing on the unexpanded case head rather than the body, odds go up that it’s holding the case cockeyed. The other area that I’d look closely at is the contact pattern from the part that contacts the shoulder, but I’m not sure how someone could measure how concentric it is to the other parts. I’d at least sharpie the shoulder to see what the contact pattern is. If it’s only contacting the angled part of the shoulder, I’d be curious to see how concentric it is there. Too much lube can create dents and uneven shoulders that are hard to see without an indicator. There’s a lot of parts that have to work together with tight tolerances for that die system to work well. You might find a friend with a more traditional Wilson seater and be able to compare results.

Since you’re going all out, I’d keep an eye out for a neck turning setup - it’s only a matter of time before you’ll want to try it.

 

[Vern400]

If I were measuring concentricity I'd want to put the v block on the neck turned portion of the case. Easy to have 0.001 of neck thickness variation alone. I only turn crappy cases, and then only to 0.0145 which is 0.0005 under design nominal. ie remove the thick spots. I don't need to turn good brass But turning it to nominal is actually just as fast as measuring it . If it's good there's almost no stock removal. On lake City, the cutter goes wop wop wop.

Unless you're shooting F Open or 100 yard benchrest you ain't missing anything because of 0.004 bullet run out. Some of it will come out when you chamber even if you jump. If you jam most of it will come out.

 

[TaperPin]

Another quick check is that the shoulder sleeve and bullet seater are concentric outside and in. These parts are all made on accurate automated high speed CNC machines, but a metal chip can still get between the chuck and raw material causing runout that might not get picked up. If you don’t have a tubing mic yet, it would pay for itself if it finds a problem, and you’ll get use out of it neck turning. It’s like a crime show - I’m looking forward to seeing where the runout is coming from.



The RCBS is a rebranded Shars with upgraded tension and locking knobs and is very good, not to mention a great value. I was concerned about flex in the long skinny anvil causing problems reading to .0001”, but measurements with my Shars on material known to be very consistent resulted in dozens of measurements that didn’t vary by even .00005” (half a tenth) one way or the other. On flat stock it measured the exact same as micrometers costing 4x as much.

 

[RockAndSage]

Seating a few bullets on some empty cases should show if it’s compression related.

Good neck lube can help the bullet slide in straighter. Neo Lube painted inside the neck is known for producing the least seating pressure.

Maybe check the contact pattern of the seating stem to make sure it’s not pushing on the tip of the bullet. A seated bullet with very little runout can be painted with sharpie and run up into the seating die until it just touches the stem - the contact should be somewhat even.

It can be misleading if the concentricity gauge is set up to ride on the rim or unexpanded portion of case head, rather than body that has been sized down since it is the body that makes contact with the chamber. Unless it’s a minimal dimension small base FL die, the body will have expanded off center of the case head some amount.

To be honest, I don’t have one and use Wilson seaters, but suspect the seating die more than anything. If the base is indexing on the unexpanded case head rather than the body, odds go up that it’s holding the case cockeyed. The other area that I’d look closely at is the contact pattern from the part that contacts the shoulder, but I’m not sure how someone could measure how concentric it is to the other parts. I’d at least sharpie the shoulder to see what the contact pattern is. If it’s only contacting the angled part of the shoulder, I’d be curious to see how concentric it is there. Too much lube can create dents and uneven shoulders that are hard to see without an indicator. There’s a lot of parts that have to work together with tight tolerances for that die system to work well. You might find a friend with a more traditional Wilson seater and be able to compare results.

Since you’re going all out, I’d keep an eye out for a neck turning setup - it’s only a matter of time before you’ll want to try it.

View attachment 873014

View attachment 873022

Which Neo Lube?

 

[TaperPin]

Which Neo Lube?

#2 is the one people are using. It’s my understanding #1.1 and #2 are roughly the same, but #1.1 meets a government spec of some kind for purity in nuclear applications and #2 does not and is half the price.