Home Forums Hunting & Shooting Ask The Gunwriters Bullet runout

Not a competitive shooter, generally try to keep runout under .003" . Has anybody ever did a comparison of .005"+ runout to <.003" for group size?
Know it effects group size, but to what extent. Never seen data relating to that.

You need to find the article John B. (Mule Deer) wrote in Handloader magazine on this subject. It will answer all your questions.

As you may already know, anything with .001-.002" runout will almost always beat rounds that are .005" plus.

It depends on the level of accuracy you're looking for--and whether the cartridge is chambered in a typical factory rifle, which may have a looser chamber than a custom rifle. It also depends on whether the ammo's full-length or neck-sized.

When I first started measuring bullet runout over 30 years ago with an RCBS Case Master, the directions suggested no more than .005" run-out for full-length-sized big game rounds, and .003" for varmint rounds.

I found that to be true--and it works on factory ammo as well. Once tested some Hornady Light Magnum 7x57 ammo loaded with the 139-grain Interlock Boattail Spire Point.

Came across three boxes for a very good price at a store in Wyoming, so ran them over the Case Master. Turned out run-out varied up to .007", so sorted the three boxes into rounds over .005, rounds from .003 to .005, and rounds under .003. The box of +.005 rounds averaged around 1-1/2" for three shots in a the custom 7x57 I owned back then, the .003-.005 rounds averaged around an inch, and the sub-.003 rounds about half an inch.

Pardon me to add a question. Who makes the best tool for checking runout at a reasonable price? I'd buy a good used one if anyone has one.

There's old articles that get into this. One of the oldest I've seen was from 1978, or so. Chet Brown was doing some testing, as he designed a concentricity gauge that could straighten and check the run out (TIR) of the loaded ammo.


In the non scientific tests I've done with it, I can say that run out does affect precision. How much, may depend on the specific rifle, since no rifle chamber, throat, bore are exactly the same.

A couple years ago, I tested some brass I received from someone here, for a new to me rifle, and the run out was atrocious. I sorted that brass, and found the straightest stuff, and did some comparisons. Here are some results, that seemed typical of this rifle and the testing I did:

Rifle: Ruger m77 mk2 300RSAUM. Glass bedded, and barrel freefloated:



Loads I tested that were pretty straight:


Loads that I tested that had a high TIR:


Retested some that had a consistent .005" TIR:

I generally don't run ammo that is this far out of concentricity, but brass is hard to find for this cartridge. I make due, but tossed everything that was .006" TIR and larger.

Tested and confirmed at 400 yards, to be sure the rifle and load is shooting sub moa out at that distance:


This testing is always done on separate occasions, different days, and most times different conditions: Wind/temps:


Those tests were done in varying temps, as there are more variables to a good shooting rifle than just one. However, if you can minimize some variables, like loading straight ammo, that will always be a positive outcome. This has been my experience. Take it for what it's worth..

Greatly appreciated well detailed info. Thanks John and bsa1917 hunter. Don't shoot in matches, but always chasing better accuracy, and this info puts it a little bit more in perspective. I knew it mad a difference, good to see hard numbers. Usually have minimal trouble keeping rounds under .003".

BSA, I'm curious that you tossed the brass with the high run out. Never tried it myself but wouldn't it straighten out from running it through a FL die then fire forming?

This topic comes up pretty regularly. The earliest work I've seen rigorously documenting the effect of runout was a pair of articles by Jacobsen and Abbatiello in American Rifleman in 1960. Abbatiello was a highpower competitor who calculated how much "bullet tilt" affected groups and documented it on target. He discussed his findings with Jacobson who was an engineer with Frankford Arsenal. Jacobson used the FA resources to more rigorously put Abbatiello's work to the test.

Here's an earlier thread where I provided a bit more detail;
https://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/15556310/1

Mule Deer, did you ever run down a copy of those articles, or do you still need a scan? They truly are cool articles worthy of the read.

Chris,

Thanks to you, I ran them down in my collection of American Rifleman magazines, which goes back to around 1930.

John

No, the brass had very uneven neck thickness variances. It was bad enough that you could see it with the naked eye. A tubing mic confirmed it though. A guy could turn the necks, but I don't have the equipment to do that. Most brass is good, but this was just a bad lot I guess?? It was R-P manufacture.

If you are maintaining .003-.005" TIR, you are doing well in my book. I always check my dies, when I set them up, and adjust them so they produce minimal runout. Some are better than others, but like you, I shoot for .003" TIR. Less is better, and up to .005" TIR is acceptable from what I've experienced. Especially if you are not shooting benchrest comps, or something like that. The extent of my "competition" shooting right now is long range varmint silhouette, where we shoot out to 800 yards. I pick and choose the rifles I use in those events, and all of my loads for those shoots are sub .003" TIR, where those rifles shoot 1" groups at 400 yards. That is my goal, at least, and straight ammo helps with that.

'Morning, John. As usual, you've brought up some good points based on experience. So much of what what we see with 'run out', (in terms of accuracy) depends on many things....primarily how the case fits the chamber, is there any amount of unsized neck to help align the neck in the chamber, how straight the throat is relative to the chamber, how long the free bore section of the throat is and the amount of 'jump' to the rifling the bullet has.

A guy can go around and around with all this stuff. For me, the bottom line is simply what a particular rifle likes....especially with a factory gun.

Here's an example of some stuff I loaded yesterday in anticipation of a few days of decent weather for testing a new gun. With a lot of attention, my setup for my 30BR stuff can hold bullet run out to right at .0005. If I change to another die that leaves a bit of the neck at the bottom unsized, the tolerance for run out can be significantly more (up to .002) before I see any change 'on target'. But if I change the seating depth from a hard 'jam-seat' to a lighter seating depth, the situation is reversed.

For a huntin' and 'dog guns, if it's around .002, I'm happy. A 50 cent rubber 'o' ring under the lock ring on a f.l. sizing die and a good inline seating die can go a long way.

Good shootin' -Al