We have another thread simmering regarding the effects of runout on rifle accuracy, and it occurred to me that we rarely if ever differentiate between the types of bullet runout, and the varying effects of the different types of runout on the target.

A brief definition: Runout simply means that the bullet is seating (or appears to be seated )in a crooked, or canted fashion with regard to the rest of the case. When the round is chambered, the bullet does not point straight into the chamber in a concentric fashion, but rather off center. When the round is fired, the bullet impacts the throat area off center, but it of course is corrected by the throat, and it continues on through the barrel.

The question as to how much if at all runout affects final accuracy is truly hard to answer conclusively. Weeding out all of the other variables is difficult if not impossible, and it would likely take thousands of rounds fired by various shooters shooting various rifles to ever come to even a tentative conclusion. And when you finally did, some bozo like me would probably still argue the point!

Anyway, one undeniable thing is that runout definitely exists. But there are different types of runout:

One of the worst and most common types of runout results when the bullet is seated askew. Not only does this start the bullet into the bore crooked, but it would also seem to have an effect on neck tension as well. Rounds of this type might be the culprit when groups go awry, and the only thing that has changed is the average runout.

Another type of runout is what I would call "case wall induced" runout. You often see this with new, virgin brass. The case wall is not concentric, even after being full length sized. The sizing die has brought the case as close as it can to uniform, but there are still imperfections that will only be remedied by fire forming. This type of runout may not really be runout at all. When you place the finished cartridge on the concentricity gauge, the out of round case wall causes the gauge to read as if the bullet is seated askew. However, it may well not be. Once this round is chambered the case neck and bullet may align near perfectly with the throat.

Case neck thickness induced runout is a biggie. If the case neck is thicker on one side than on the other, it will cause the neck to be out of line with the case body when the case is sized. Seating a bullet into such an abomination will result in a cartridge with excess runout, and fire forming will not solve this problem. Neck turning, or trashing the cases (my choice) are the only solutions.

Yet another type of runout that your concentricity gauge can go bonkers over is "case head out of square" induced runout. In this scenario, the case head is out of square with the case body. This is sometimes seen on virgin cases, and also on fired cases coming from rifles with out of square bolt faces. (Better sizing dies may correct this, but run of the mill dies with conventional shell holders will do little to solve the problem).
Since the case head is held against a stop post as the case is being rolled, if the case head is out of square the cartridge will oscillate front to rear. If the runout gauge's ball is sitting on the ogive of the bullet, considerable variations will be seen on the dial. While this type of runout may be only realted to the out of square case head, it is likely that the case is sized out of spec as well, due to the effect that the askew case head would have on alignment during sizing and bullet seating.

Lastly (though there are probably other forms I've forgotten to mention) is bullet runout. This means just that--the bullet itself is poorly made and not concentric. Rounds with this type of runout probably fare worse than all others combined.

My point in all this is that before you can say unequivocally that runout does or does not affect your rifle's accuracy, you have to identify the type of runout you mean. Case wall induced runout may have little if any effect on groups. Someone shooting a box of such cartridges might conclude that runout is "no big deal." On the other hand, case neck thickness inconsistencies , or crooked seating of the bullet will likely (in my opinion) affect the groups to some degree.

Thanks for the read,

Dan Newberry
green 788

Dan....

You REALLY like throwing that big monkey wrench into my works!

But honestly, I really enjoy reading your findings and I find myself 'looking' for your threads on the little pitfalls that keep us from our perfect load.

Keep up the good work.

Oh....if you can find it in your heart,,,try throwing some postive 'light at the end of the tunnel' stuff our way!

TXPO, Thanks for the kind words... I suppose the "positive light" here is that every time the runout needle twitches that isn't necessarily a bad thing.

I tested some cartridges this afternoon in my Savage .243 win. The brass was new (virgin Winchester), and runout was noticeably higher than on fire formed brass.

However, the load shot 1/2 to 3/4 MOA for two strings of 5 shots at 200 yards--in the rain...

75 grain Hornady VMAX, 39.0 grains of IMR 3031. I tested this twice through using the OCW test, and it showed in both cases that 39 grains was where to be--even though seating depth was .010" longer on the second go.

Anyway, thanks again for the encouragement...

Dan

You wouldn't happen to have a .35 Whelen lying around that you can run through your OCW test to come up with some powder/bullet weight combos, would you???? I figured that since you are the PRO at it then it would save me lots of time!

Just kidding.......someday I would really like to take a serious stab at your procedure some time. Keep up the good work.

TXPO,

You're too kind...

If you're going to work with the Whelen, the 250 grain bullets seem a good choice. Beginning with one cartridge loaded with 54.0 grains of W748, and another loaded with 55.0 grains of that same powder, take a couple of sighter/fouler shots at 100 yards. Zero for as close to the bull as possible, then go with the OCW work up using three each of the following:

55.5, 56.0, 56.5, 57.0, and 57.5 grains of W748.

That should be one of better velocity attainers in this application. W748 can be temperature sensitive, but not so much to cooler temps. Unless you're out and about in 85+ degree weather, I wouldn't concern myself there...

Take care. If you were thinking of another bullet weight, let me know...

Dan