Bullet Concentricity

I use the rcbs gauge. I use cartridges with .001-.003" for groups and with .004" or more for fouling and whatever. the accuracy difference isn't much, but it is there. I have noticed that cases with a lot of runout never get "better" and cases with little runout usually stay "little".

luck,

murf

I’ve shot side by side rounds with increased runout up to .006 with absolutely no difference in point of impact.

Maybe I’m doing something wrong...

I use a Hornady concentricity gauge, for me it not only improves my reloading skills it cuts down on fliers.

You seem to be groping at straws here for some reason. You have to have the right setup to take advantage of what a concentricity gauge brings to the table. In your neck turning thread I did a post using a savage axis. That axis has a factory chamber with a llloooonnnnnnggggg throat. I have to step up to 69gr bullets or longer to get the bullet to sit in the leade of the throat to be able to take advantage of a concentric bullet. Otherwise the perfectly aligned brass/bullet is going to have side to side movement/play in the chamber.

When you hit the loud button your reload is going to go to the least point of resistance. Any play in the brass/chamber fit means side to side movement. Bullet isn't set so it sits in the leade of the chamber and there's side to side play/movement. Differences in the brass hardness will come into play magnifying the movement/lack of movement for the same reloads.

What your trying to do (watered down version):
It starts at the back of the bus & how true the bolt face is to the chamber. Serous shooters have their actions worked/trued or some mfg's like savage use a floating bolt head that squares the brass to the chamber. The chamber's body and your reloading dies should match. Dimensions like how much you size the body down or how far back you set the shoulder are important. That's why a lot of people only neck size their brass when reloading for the single shots/bolt actions. The brass's neck plays a huge role in accuracy consistency. Measure your reload & measure your fired cases. This will tell you what kind of play you have in the neck area and how much neck tension you have to play with. The bullet should not only sit into the leade of the chamber the angle of the bullet's octave should match the angle of the leade. A picture of the leade/neck area of a custom 308w bbl.


I've used apache bbl.'s that were cut for the 175gr smk bullets in the 308w in the past. Still have 1 laying around with a 100 round count down the tube in it. Worked up a load then took it off the rifle. The bbl pictured above is a custom shilen bbl that is 30" long, is 300"-308" 6r, chambered in 308w match with a .340" chamber and a 1 in 14 twist. The leade is cut for the 155gr smk palma bullets. I actually bought the bbl for shooting cast bullets. That picture was taken after 1000+ rounds with cast bullets thru it with 700+ of them loaded with 30,000+/- psi loads. As you can see or more importantly what you don't see is any wear in the leade's. The .340" is the size of the neck of the chamber, wanted that for the thicker lc brass and larger .310/.311 cast bullets.

Why all this?
Because you need to measure your fired brass, figure out what leade you have along with any wear/damage in that area. The measure to see if you can even make the oal of your reload long enough to fit into the leade of the throat of the chambers. How generous the necks in the chambers are along with if the ball throat is still there and concentric.

At the end of the day:
Neck turning and concentricity gauges are going to do much for you if your bolt face isn't true to the chamber OR.
Your brass is sized smaller than 1/1000th's in the body & neck area and 2/1000th's max at the shoulder length compared to the chamber.
The bullet you chose can't be loaded long enough to fit into the leade of the throats
If the throat was either cut too long, cut wrong, erosion, offset doesn't matter want you do
Then you can get into things like brass, consistent ignition, powders and their short start pressures.

A good place to start is by looking at your bolt faces and pitting. Too much pitting with a low round count is not a good thing.

Sorry for being long winded but you need to actually do some measuring to see if any of the things your asked about will make any difference in accuracy in your rifles. If your reloads are sitting 1/8" off the lands it really doesn't matter what you do. 10/1000th's" or less into something that isn't eroded or worse, it's game on.

My experience with the RCBS tool:
1. I found that the biggest nasty causing run-out is the expander ball in ordinary sizers. It stretches the necks on the way out, worst for hard (old) LC brass. With that brass I found that I could make the best difference using an RCBS lube pad correctly (keep off the shoulder) than using Imperial, or lanolin spray lubes. You know with that brass when you are stretching one....it's harder than hell sizing and pulling the expander out.

2. I found that resizing 2 more times, rotating the brass 1/3, I could make .006-out brass .000 or .001 every time. I realize that hardens the brass more, but after doing that and shooting great groups with it, the plan is to anneal before loading again......I have yet to do that....still shooting the stuff the first time.

As for the RCBS tool, it works fine, and it's great for the price, but there are more esoteric tools.....by that I mean more expensive and easier to use. I have no experience with the Hornady tool, which is used to push a bullet sideways.....others can tell you if that really works on targets.

3. The other big nasty is that just because you straighten the case perfectly, does not mean your seater will seat the bullet concentric. My testing isn't complete there, since I've tried the Gold Medal seaters, (better than regular) but have not tried other brands of competition seaters......all bets are off on a regular seater without full length bullet support. RCBS is phasing out the GM seaters for their new line, I have no idea if it is an improvement or a name change, having never seen/compared one.

These FL dies do not incorporate an expander, only a decapper.
www.lewilson.com

The subject of cartridge/brass/bullet runout, and the various tools and techniques for measuring it always get my attention. The first question that always comes to mind is where on the cartridge is the measurement taken?

I have built a couple, the largest benefit they have given me is a way to quantify changes in equipment and process, in relation to the final product. They don’t make more accurate ammunition but they have taught me what I need/don’t need to do to make it though.

Got into concentricity checking with a target\varmint gun years ago, it started me down the road to match prepping my loads. Like already mentioned the number one result is you will notice which dies are producing pretty straight ammo and if you're tweaking the necks when you resize. I first used an RCBS unit and it was great for measuring run-out but most gauges aren't equipped to fix the issue. I started using short hunks of reamed out barrel ends and it was a long game of tweaking and rechecking to get them under .001. The Hornady caught my eye and I bought one, they have a thumbscrew that you can push the bullet some and recheck in one step without removing the cartridge. I press about 1/3 way out the bullet from cartridge neck. If you're dies will get you to under .004 its pretty easy, but it will still take several tweaks to bring them down to .001. Redding dies are my favorites for using, forester dies are good as well. You still need a gun that will shoot an inch or less at a hundred to really see the difference, and it should be a good accurate handload with things like distance to lands-powder type-charge weight-primer- and brass manuf. already honed in. I'll do a review on the Hornady gauge sometime and give some tips on how to make it better than out of the box (I killed the thumbscrew pad in about 50 rounds) Woods

Just finished making this one this week.

When you hit the loud button your reload is going to go to the least point of resistance. Any play in the brass/chamber fit means side to side movement.

Click to expand...

One doesn’t need a way to measure runout to eliminate tolerance in brass to chamber.

Remove the tailstock/firing pin from the bolt and adjust your size die so the bolt only drops half way on a sized case.



Now you are guaranteed for the case to be tight in the chamber when the bolt is fully closed. Also extends brass life because it’s not being undersized, blown out, sized again and trimmed to repeat.

I put my money into the best competition seating die I could find and skipped the concentricity gauge.

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Bill M. said:

I put my money into the best competition seating die I could find and skipped the concentricity gauge.

Click to expand...

That’s great but IME most runnout is introduced during the sizing phase. With regards to seaters the one with the least influential runnout I’ve ever seen is a cheap Hornday.
J

South Prairie Jim said:

That’s great but IME most runnout is introduced during the sizing phase. With regards to seaters the one with the least influential runnout I’ve ever seen is a cheap Hornday.
J

Click to expand...

I too have found sizing and expanding a case and causing runout can’t be fixed in subsequent steps of the reloading process.

Why I use the first device in #8 more than the 2nd as it can check fired cases to see what the chamber has blown it out to and every step after that, back to a fired case again.

I used to check every round for runout but after upgrading my sizing dies runout was reduced to point where I don’t need to check it