Bullet / Case concentricity

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brent373

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There are lots of tools available today for checking, and even correcting the concentricity (runout) of a bullet in relation to the case in which it is planted. I have heard/read many OPINIONS varying from: "Runout does not affect accuracy and consistency", to "I wouldnt go without a runout correction tool".

I have some of my own presuppositions, and not so objective data that says runout does create flyers, but have never performed a controlled experiment to gather any concrete evidence.

My question here, is this:

Has anyone (using a concentricity correction tool) shot a controlled group with ammo that has been verified as untrue by .003-.005" back to back, with a group shot with ammo verified true to .0005 -.001" with the same rifle, on the same day in the same conditions etc etc.

My apologies if a thread exists on this already. :)
 
I did an informal test at 300m with 5 rounds that were .003 (possibly .004, this was 2 yrs ago) out of concentric.

I marked the 5 rounds with a marker where they topped out the guage. I then shot 4 rounds with the mark facing up when put into the action. The 4 rounds shot higher than my previous known good rounds but all 4 shot into the same place. I then placed the 5th round into the chamber with the mark facing down and the final round landed below known good rounds.

Now at 300m (on the old ISSF F-class face) the 4 rounds were in the upper part of the 10 ring while the last round was in the lower portion of the 10 ring. On a new ICFRA face these would most definitely been 4's as there was approx an inch to inch and a half (or more) difference in the POI between the 4 upper and the 1 lower.

Again, this was informal but surely opened my eyes to the effect of non concentric rounds.
 
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Interesting question.
I am preparing the following rounds for testing - just waiting for the wind to die down a bit.
Components are:
SMK 175 gr HPBT (sorted by bearing length only)
Reloader 15 = 39.7 gr
CCI BR2 primer
Hornady brass (sorted)
All bullets were seating by Redding Competition seater
Rifle SAKO TRG-22.

Rounds loaded:
3 rounds with original meplat (less than 0.002" run out)
3 rounds with origonal meplat and concentricity adjusted (less than 0.001" run out)
3 rounds with meplat adjusted (less than 0.002" run out)
3 rounds with meplat adjusted and concentricity adjusted (less than 0.001" run out)

This is not exactly control experiement. But I am hoping it will tell me whether concentricity is critical for my rifle.

Testing range distance will be 300 yards.

Just for kicks, I measured 10 rounds of Hornady 168 gr AMAX factory ammunition concentricity. The run out ranges from 0.0005" to 0.002".
 
The rounds I tested (now that I think back) would have been .005 of runout since I do use anything .0025 or less in competition.

Doubtful you will see much of a difference in those loads you have listed.

Do load some up and adjust runout to something outlandish and see if they make a difference.
 
I'll be very interested to find out results. Another thought.... Those hornady A max factory loads...what if you were to separate them in groups. I mean find a few rounds that are
.0005" - .001, and then a few rounds that are closer to .002", and try shooting groups with each. I would do this myself but do not yet have a conc. tool :)

To take barrel heat out of the equation, one could alternate, shooting one of the straight rounds, followed by an untrue one, or do the unthinkable and wait 5 minutes or so between shots ;)
 
Even though we are all for the least amount of runout, are we sure that the bullet is indeed introduced to the rifling concentrically? Is the case perfectly centered in the chamber and not "sitting at the bottom of the chamber"(gravity). These concerns go way back in time and why to this day, some folks breach seat soft cast bullets, because it is physically easy, whereas it would be impossible with jacketed bullets.
 
ben hunchak said:
Even though we are all for the least amount of runout, are we sure that the bullet is indeed introduced to the rifling concentrically? Is the case perfectly centered in the chamber and not "sitting at the bottom of the chamber"(gravity). These concerns go way back in time and why to this day, some folks breach seat soft cast bullets, because it is physically easy, whereas it would be impossible with jacketed bullets.
Click to expand...

That's where a tight fitting throat (.0005) clearance in a custom chamber has it all over a loose factory throat. The bullet is kept in line with the barrel despite run out, and gravity.

NormB
 
Made a test last summer with my friend's runout guage...The worst shoots better groups...Now man I can't tell the difference and did'nt buy the guage.Me thinks the guy
behind the gun is the problem...LOL
 
NormB said:
That's where a tight fitting throat (.0005) clearance in a custom chamber has it all over a loose factory throat. The bullet is kept in line with the barrel despite run out, and gravity.

NormB
Click to expand...

That's what I was getting at, many will be spending alot of time and effort trying to get concentric rounds and have a sloppy factory chamber.
 
NormB said:
That's where a tight fitting throat (.0005) clearance in a custom chamber has it all over a loose factory throat. The bullet is kept in line with the barrel despite run out, and gravity.

NormB
Click to expand...

I do all that I can to limit runout BUT I have shot some really wonky ammo at 200yds and it still shot great. My comp stuff usually has 2thou and under.

In general, the diameter of the throat is not a big deal BECAUSE, the bullet should be fully engraved in the rifling long before the bullet ever leaves the case mouth.

If the bullet is fully supported by the rifling, how can it wiggle thus making the clearance in the throat moot.

If the throat is too tight, it can actually cause more harm then good. Fouling, moisture, variance in bullet diameter can conspire to cause major issues during the firing cycle of that cartridge.

With F class, I go with good ole SAAMI clearances BUT with a short leade relative to the seated bullet that I am using.

So far, it has kept my rifles functioning even in big rain and I can extract a loaded rd without fuss.

As for accuracy? Well inside the V bull as far as I compete. At least the rifle can shoot that well :rockOn:

Jerry
 
ben hunchak said:
That's what I was getting at, many will be spending alot of time and effort trying to get concentric rounds and have a sloppy factory chamber.
Click to expand...

Fireform your brass before doing any serious load work up. Neck and body size to maintain a nice fit to the chamber - issues with an oversized chamber dealt with.

Find the actual leade distance for your rifle and load accordingly. For mag fed rifles, you may have to seat the bullet aways from the start of the rifling to function BUT as long as the bullet is well and truly engraved before it leaves the rifling, this shouldn't limit accuracy potential.

Powder tuning plays a major role here.

A properly fireformed and sized case with a bullet seated true doesn't care how much space is around the case neck. The only thing that matters is when that bullet engraves the lands.

If this happens in a positive manner, you are then limited by the quality of the bore vs bullet vs load vs shooters skill.

Jerry
 
How do you know if and when the bullet enters the lands squarely? The only way you could be sure is if the bullet "flats" are being squared into the rifling. This goes along with the origins of "breach seating".
 
You have to start with a straight chamber vs the boreline. Take a chamber cast to confirm.

With fireformed brass properly sized and bullet seated, the case MUST follow the direction of the chamber and if that is straight, so will the engraving of the bullet to the lands.

That is why I say, the most important part of any precision rifle is the chamber. No matter what else, if this is wonky, the gun will never shoot.

Oh by the way, the odds of seeing a leade with exactly the same depth of rifling in each land is not good... not that it matters.

check again in a couple of hundred rds and it will have changed so it plays a very small role.

More important is that the bullet fully engraves in ALL of the lands long before it leaves the case neck.

Jerry
 
Im very much following what is being said about the chamber to bore axis being critical, and perhaps this is a silly question, however, IF cases are first fireformed, and properly resized so that an ever so slight amount of drag (almost unfeelable) is present when closing the bolt on the empty case, a perfectly concentric, loaded round will see the bullet meeting the bore at the same angle, in the same place, with each shot. In a perfect world where all bullets are cast identical, if say they were machined instead of cast, and mass was evenly distributed around the axis of the bullet, etc. etc., could an untrue chamber to bore configuration be capable of being a shooter ? Afterall, even a broken can opener will malfunction the same way each time :)
 
brent373 said:
could an untrue chamber to bore configuration be capable of being a shooter ? Afterall, even a broken can opener will malfunction the same way each time :)
Click to expand...

That where the shooter himself comes into play, and knowing your gun.
I've got a .22 that is really consistent, yah consistently high and to the right. :p
 
Depends on how wonky it is and what the shooters expectations are.

For the SR BR game, odds are you are paying for another barrel.

For F class, you may not notice.

for a hunter, you may think it a superb install.

Jerry
 
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