Centerfire Rifle Cartridge Reloading: Correcting Bullet Runout:
Bullet runout is the cause of most reloaded rifle cartridge inaccuracies. Most rifle cartridge case and bullet alignment is determined in the resizing die but there are other reasons and situations that will cause excessive bullet runout which are not readily seen with the human eye.
Bullet Runout Depiction:
The below cartridge centerline drawings are slightly exaggerated for viewing and demonstration purposes of bullet runout.
(a) .000″ – .002″ Bullet Runout.
(b) .003″ – .004″ Bullet Runout.
(c) .005″ – .010″ Bullet Runout.
Determining or Diagnostic For Bullet Runout:
The above conditions will go unnoticed by most reloaders because you have to check bullet runout with a accurate run-out gauge. If you go to the range and are consistently frustrated with group size and bullet flyers out of a good group and you have followed the steps in my accuracy guide read on.
Bullet Runout Correction:
Bullet runout correction begins right after the resizing die step of once fired cartridge cases in rifle cartridge reloading.
1. Cartridge Case Resizing:
Once you have resized a once fired cartridge case the next step is to check case-neck runout which should be less than .002″.
Note: If you are working with new unfired brass do not try to take accurate runout measurements other than bullet runout as brass needs fire formed one time to give consistent true readings.
1a. All cases that have more than .002″ neck runout should be set aside and checked for case neck thickness, if this is the problem the necks will have to be turned and trued.
1b. If your runout is consistently more than .002″ and case neck thickness is not the problem you should check to make sure that your resizing die is clean and properly set, if problem still persists a tighter tolerance resizing die should solve the problem.
1c. At this point you will realize that some brass cartridge casings are going to have to be weeded out and not used. With all work done at this point separating process should be as follows:
.000 super accurate,
.001 very accurate,
and beyond–.002 trash can.
2. Trimming, Chamfering and Deburring:
The next very important step with the cartridge case to minimize bullet runout is trimming, chamfering and deburring.
Trimming cases can be done by many different types of tools but the bottom line is the case mouth has to be cut true to facilitate the bullet seating operation minimizing bullet runout.
Case Full Length Trimming Depiction:
The below drawings are exaggerated for viewing and demonstration purposes of full length trimming.
(a) Trued Cut.
(b) Angled Bad Cut.
In the above drawings (a) when properly chamfered and deburred should allow proper bullet seating, (b) when chamfered and deburred will not allow the bullet to be seated properly and it will cause bullet runout.
Chamfering cases is normally done by hand with a hand tool and leads to a lot of bullet run-out problems. Chamfering cases needs to be done exactly the same on each and every case with machine like accuracy.
Case Mouth Chamfering Depiction:
The below drawings are exaggerated for viewing and demonstration purposes of case mouth chamfering.
In the above drawings (a) properly chamfered should allow proper bullet seating, (b) chamfer to deep and will most likely leave slivers of brass in your rifles chamber causing accuracy problems, (c) chamfer to shallow will most likely shave copper from bullets causing accuracy problems and will cause bullet run-out, (d) angled cut will most definitely cause bullet runout.
Deburring cases is normally done by hand with a hand tool and can lead to some bullet runout problems in certain bullet seating dies. Deburring case necks needs to be done exactly the same on each and every case with machine like accuracy.
Case Neck Deburring Depiction:
The below drawings are exaggerated for viewing and demonstration purposes of case deburring.
(b) Not Deburred.
(c) Angled Deburred.
In the above drawings (a) properly deburred will allow proper bullet guide and seating in all dies, (b) not deburred will have some effect on bullet seating in certain dies and will create accuracy problems inside the rifle chamber, (c) angle deburred will have some effect on bullet seating in certain dies and will create accuracy problems inside the rifle chamber.
3. Bullet Seating:
The bullet seating operation and bullet seating dies vary between manufacturer of these dies, I classify bullet seating dies into 2 classes.
3a. Standard reloading dies (which is the accepted standard). These dies will yield bullet runout generally less than .005″. Standard bullet seating dies will seat bullets straight if the bullet is set on top of the piece of brass straight before you slowly lower the press handle to seat the bullet.
3b. Bullet guided dies which are classed as (competition dies). These dies will yield bullet runout generally less than .003″. Competition bullet seating dies have a collar, collet and or guide that automatically guides the bullet into the piece of brass straight reducing the human error factor.
1. If your looking to gain a little more consistent accuracy than what you are getting now from your handloads. I highly recommend if you own a RCBS case trimmer, trimmer 2 or trim pro to add the RCBS Trim Pro 3-Way Cutter. Different caliber pilots are available.
RCBS Trim Pro 3-Way Cutter.
Trims, Chamfers & Deburrs with lathe like accuracy. Its unique 3-blade head trims cases like a standard cutting tool, the inside blades chamfer the case while an outside blade deburrs it. Excellent tool for precise bullet alignment and seating.
This tool is simplistic in design and easy to use and a must for diagnosing cartridge problems that are not readily seen by the human eye. How the complete cartridge fits in the chamber and throat of the rifle barrel directly affects accuracy. The RCBS CaseMaster® Gauging Tool, measures case neck concentricity, case neck thickness, case length and bullet runout.
Tight machining tolerances of these dies yield maximum concentricity between the die neck and body. The bullet seater die features a micrometer bullet seating head that lets you adjust the seating depth you want in .001″ increments. There is also a handy bullet window machined through the side of the die to allow much easier bullet insertion. Plus a special bullet seating sleeve assures correct bullet alignment before, during and after bullet seating.