Does concentricity make much difference?

[Montana Pete]

My new Sinclair concentricity guage arrived at the door a few days ago. At that time I happened to have a couple of boxes of ammo already loaded for the 22-250, so I decided to run them through the new guage.

After running one of the boxes through, I identified five cartridges out of the 20 that had more run-out than the others -- around 4 to 5 thousanths of an inch. The others had little or no run-out. I set the former aside.

At the shooting range yesterday I decided to use the five hi-runout shells to warm up the gun before settling down to serious shooting. I expected they would not shoot so good.

The five with the run-out produced a 0.434 inch five-shot group at 100 yds. Subsequent shooting with the "good" rounds did not do this well, producing at best just a 0.75 group.

Not enough rounds were fired to conclude too much, and there was a tricky cross wind that also complicated the picture. But . . . .

. . . . I am beginning to wonder if bullet run-out is very important -- at least, in my present rifle. I may be measuring something that does not have much significance. ? ? ?

I attach a photo of the new guage measuring a 22-250 cartridge. It seems to be a real high-quality product and I wlll continue to use it and try to learn something with it.

 

[Old Gunner]

A concentric cartridge is most important when reloading for a rifle which has a relatively loose chamber.
I mark each rim to be sure of orientation on first firing then rotate 180 degrees on second firing to ensure equal expansion of the case body.
I necksize only the first 2/3 of the neck, the equally expanded rear of the neck centering the bullet to the origin of rifling.
Those steps greatly reduce group size.

When a rifle has a good tight chamber and throat the benefits if any of such steps would be far less noticeable.

 

[P1ZombieKiller]

question

I am also looking into purchasing one of these to help with my shooting. I "ASSUMED" that you measured the "loaded neck" of the cartridge as this will be where the cant or tilt is. I assumed that even if you have a perfectly round bullet, if you set it in your case at a tilt, that this will cause your bullet to jam to the left or jam to the right.

I am very new, and I apologize if my little mind has things messed up.

 

[guitarguy0731]

Montanta Pete: Those are some interesting results and I'm glad you posted them as I was wondering the same thing. I have a forester concenticity gauge that I use to measure case neck thickness and runout when I turn my Necks and was wondering if it was worth my time to check the runout also of the finished cartridge.

You mentioned that your "good" bullets didnt' shoot as well as the "bad" bullets. Could it be the order that you shot them in maybe? I know that my gun is most accurate on shots 2-7. The first shot is usually not the best, then the next 5-6 shots or so are basically through the same hole, and after about 7-8 shots I think maybe my barrel is beginning to heat up or get slightly dirty. Maybe that is what happened with you? I wonder if maybe you shot your "good" bullets first if those would have grouped better, and then shot your "bad" bullets next they would have opened up? Just a thought, but back to your original point...It seems from your shooting that the high runout, regardless of when you shot which bullets, did not affect your groups to any significant degree at all. Perhaps you would notice those subtle differences in runout at further ranges. 100 yards is probably too close to draw any conclusions. I know my gun will shoot anything good at 100 yards, its not until about 200-250 where you can start to notice the results of tweaking different variables. Anyways, just some thoughts that I'm sure you already thought about. I'm glad that you have tested your bullets with the different runout because that also helps me answer the question of the runout in my own bullets and their importance. I've always read that any runout greater than 0.001" is too much, whether it is in neck thickness variation, concentricty, or the finished cartridge runout. Hope this helps a little.
Matt

 

[alinwa]

No

al

 

[Boyd Allen]

When I use a concentricity checker such as the Sinclair, I use it several ways. First, on my bench rifle that has no ejector to oval the fired case necks, I may check the fired cases, near the ends of their necks. They are not identical, and the ones with the most runout, will usually have the most after sizing. After sizing, I may make the same check, to see how my die is doing. Later, after bullets are seated, I will take a reading on the bullet about .150" from the end of the case neck. I all cases, I position the front case support as close to the shoulder as I can. When there are forum discussions on runout, if we don't know where the cases are supported and where the readings are taken, results will not be comparable, from poster to poster, but we can learn what reduces runout.

 

[jackie schmidt]

Concentricity

In Benchrest, aquiring dead straight rounds is one of those things that we strive to achieve, we just had a thread running on this very subject.

.005 is a lot. More than I would certainly settle for. But is it toomuch. In all honesty, I do not know.

Is sticking a round that runs out .005 the same as having a chamber that has a body running out .005 with the lands and grooves? If a Benchrest Gunsmith consistantly chambered barrels with the chambers that far out, I doubt he would be in business long.

The best thing to do is strive to get your dies to produce as straight of ammunition as possible. That way, you can at least sleep well........jackie

 

[OldPPC]

...The best thing to do is strive to get your dies to produce as straight of ammunition as possible...

Best advice, IMO, posted thus far. It's not something I worry about when I'm eliminating varmints from an agricultural environment, but if it's punching holes in paper that are closer together than the guy next to me, "straight" makes a difference in my day.

 

[f d shuster]

Runout

Montana Pete: I use the same Sinclair gauge to check runout, have been doing it for years. My "solution", ( works for me), is to identify and segregate the occassional round that has what I consider to be unacceptable R/O, and that depends on it's intended purpose, and use it accordingly. My limits for a match and longer distances is .002". Anything over that will be marked & kept for first round foulers, basic scope adjustment, and closeer distances. As you, I've fired some really nice 5 shot groups at 100 & even 200 with R/O that measured as much as .005". When these R/O loadings pop up I write them off as a defective piece of brass, from when that piece was drawn. I'm using Redding neck bushing dies, Forster micrometer BR seaters, Wilson chamber seaters with an arbor press, Lapua brass, etc. etc., and can still get R/O. I've measured new,unfired factory ammo and found R/O of as much as .012", so bad you can watch the bullet tip, and sometimes the entire neck jump up and down as you smoothly rotate the ctg. under the dial indicator. How's that for the so-called superiority of factory ammo?

 

[bluechip]

Runout

I bought a hornady runout checker for 17 HMR's. I had to modify it a bit, but the problem was that the rim was .010 out of concentricity with the case body, so you can't locate on the rim. Here's a tip. When you check centerfires with the type of checker that locates the cartridge between two cones, try putting the indicator near the case rim and check runout. My 222 lapua's were out about .002, so I modified a sizing die and indicated it dead nuts in a four jaw and recut the rim a coulpe of thou. to true it up.
If anyone here is familiar with a punch grinder, I run a box of 17 HMR's through it ( "V" block locating the case body) and found, out of fifty, 6 less than .001, 12 .002, the rest .003-.004 with one being out .007. Here's the head shaker, they all grouped the same. Even the worst one shot right into the center of the guns grouping.
I stubbornly will continue to use it on my 6PPC because the bullet is barely into the case, and every round is a couple or so out, but it may not be doing anything to grouping. I guess it's more of a mental thing.

 

[jackie schmidt]

German

It has been my experience that most runnout is induced in the sizing proccess, and even the best seating die will not produce a straight round if the case going in is not dead straight.

That is one reason I do not use bushing dies.........jackie

 

[abintx]

Jackie ... German ...

Jackie, I agree on all counts - it's all in the sizing (and brass quality) and bushings induce more runout. I still use bushing dies for convenience, but just had a .308 and a .30-06 die neck reamed to my preferred neck sizing dimension (0.31") and am beginning to work with those. I'm happy with what I see so far!

Which or whose dies are you using and who is doing the reaming? Where does the average guy go to have it done? Art

 

[John S]

New Quality Brass

Does anyone set aside new unfired brass that doesn't make the concentricity test?

Or do you fire-form it before you decide it needs to be tossed?

I just found about forty rounds of unfired Norma that I set aside a few years ago that is running .004 out on the neck. The barrel is one of the straightest Hart's ever put on a lathe with a fine custom chamber.

Thanks

 

[alinwa]

John S,

New unfired brass CAN'T be concentric, it's just a raw product that's been formed in a hammermill. Cases cannot be concentric until they've been fired a few times. (IMO)



And on the subject of concentricity:

If cases don't come out of your rifle concentric, they can't be fixed.

If your dies don't fit properly to maintain the brass, it can't stay concentric.

If your rifle DOES produce straight cases and your dies are sized/mfgd such that they keep the rounds straight through the reloading process then you are golden

In short, it is my opinion that if your rifle doesn't make straight cases and if your dies don't keep them straight then you must go clear back to square one and start over..... find the runout. No amount of measuring/culling/sorting/straightening/fixing will allow you to find the system's potential.

Of course others, MOST others disagree... ..... and will fold spindle and mutilate cases old and new in an attempt to "make them straight." And will believe that the results speak for themselves, that straighter ammo shoots better.

al

 

[OldPPC]

Re: your question JohnS - I try to fire form all of my brass with a moderate load before I reload for the competition or serious load testing. That may be anal but I don't want to set things up using "fresh" brass, whether it's straight or not, and then have to rely on it after it's reloaded and reformed.
I have to agree with what German Salazar offers above. Perhaps the concentricity thing is overplayed but if it's nothing more than a placebo I still feel better knowing I'm centered when the pill starts down the bore.

 

[VaniB]

I personally don't find the 4 to 5,000ths readings on the Sinclair gages to be the real problem cartridges with producing at least sub 1/2" groups. But the gage sure does easily and quickly identify those 9,000ths and worse readings that do occassionally happen. Those kinds of cartridges often materialize into flyers.

If you don't put your cartridges on the gage, how will you know what you have? Of course, some guys are so good at hand loading, that they will tell you that their methods and experience always make perfect rounds that don't require checking.

I'm not going there again. Decide what you think is best for you. Hope this helps. Bye.