Home Forums Hunting & Shooting Ask The Gunwriters Bullet runout

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..