If you are a precision shooter, you care about consistency for the cartridges that you shoot. One of the most important factors to measure and control when reloading match ammunition is bullet concentricity. Simply stated, this is the alignment of the case and bullet. If you have “good concentricity”, you will have the axis of the bullet and the axis of the case close to collinear (on the same line).
In this video, we’ll measure the concentricity of the ammunition that we’ve been loading in AR-MPR Phase II – specifically when we seated the bullets in the previous video: AR-MPR Phase II – Seating Bullets. We’ll also use the included adjustment screw to dial in our runout (lessen it when needed) so that we have +/- .0005″ measured runout. Note that each measurement tool measures runout differently, so you’ll need to factor that into your goals for your own match ammunition.
In addition to checking and correcting your own handloaded ammunition, this tool is also great for checking and dialing-in off the shelf commercial ammunition. I might just have to go through some of my prior loads in different calibers to see how well I did!
7 thoughts on “AR-MPR Phase II – Checking and Correcting Bullet Concentricity”
I always wondered what that tool did and how it worked. Did you do any sort of crimp after your bullet seating video? What are your thoughts on crimps for auto-loaders?
Also, when adjusting concentricity, does the action of doing so change the dimensions of the neck any? When using a progressive press I notice that during the seating stage if a bullet accidentally tipped over ever so slightly while being seated it would sometimes deform the neck (sometimes barely noticeable to the eye). I end up pulling the bullet, resizing the neck (minus the decapping pin), and continue throughout the stages.
John- I’m not crimping for these loads (bullets don’t even have canellure). I don’t think crimping is necessary for most AR shooting, but military ammo is crimped due to their requirements.
The action of tweaking the bullet is the same technique (basically) that benchrest shooters have used for decades. By tweaking runout by .001″, you don’t at all ovalize the case mouth. Now, if you were doing a .100″ correction…. (you’d have bigger problems… 🙂 ). Indeed tipping bullets when seating is a problem. That’s why I like the Hornady seater, and the Redding competition seating die. The sliding collar design helps prevent bullet tipping.
Kinda off the subject, but I couldn’t help noticing the new benchtop with the rails! I like the idea of having the concentricity gauge, case trimmer, etc. on seperate plates that lock in to the rail. Where did you get the rails and or bench top?
Thanks always for the great site and welth of information.
BTW: I posted the follow-up here:
Have you checked to see if the bullet seating depth is ever affected by nudging with this tool?
after checking and correcting concentricity could the round then be crimped to keep that setting firm?